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STARDATE FAQ Star Trek Gallery


Version 1.6
by Andrew Main



I.1. Table of contents
I.2. Introduction to this FAQ
I.3. Abbreviations

II.1. The official explanation
II.2. Subjective stardates
II.3. Mission-based stardates
II.4. Modified Julian dates
II.5. Hexadecimal stardates, ten year centuries and other rubbish
II.6. Recalibration of the warp factor scale

III.1. Time standards
III.2. Principles for the investigation
III.3. Reference points: the original series
III.4. First period of stardates: the original series
III.5. Reference points: the classic films
III.6. Third period of stardates: the classic films
III.7. Second period of stardates: intermediate, ST:TOS to TCFS
III.8. Reference points: the next generation
III.9. Fifth period of stardates: the next generation
III.10. Fourth period of stardates: intermediate, TCFS to ST:TNG
III.11. Zeroth period of stardates: before the original series

IV.1. Conjectural history of stardates
IV.2. Date calculations
IV.3. Stardates in the twentieth century

V.1. The Klingons wouldn't use a human-based system
V.2. There aren't really any stardates below 1000
V.3. The 4 at the beginning of TNG stardates means 24th century
V.4. It wasn't winter on stardate 44012.3
V.5. Riker's beard was four years old, but this system makes it five
V.6. This system gets Sarek's age wrong
V.7. Sisko said his wife died four years before stardate 47329.4
V.8. Stardate 49263.8 was an anniversary of the arrival of the Emissary
V.9. Stardates in the 30000s were 35 years before stardate 47254.1

VI.1. Obtaining the latest version of this FAQ
VI.2. Obtaining this FAQ in other formats
VI.3. Related material
VI.4. Contacting the author
VI.5. Acknowledgements
VI.6. History of the text
VI.7. Legal notice


There are a number of conflicting theories concerning the meaning of stardates. This is primarily because no entirely perfect system is possible. However stardates are defined, the definition must have changed more than once during established Trek history.

This FAQ is an attempt to answer once and for all questions concerning the nature of stardates. The system worked out is as satisfactory as is possible in these conditions of confusing and conflicting data. Unlike most FAQs, the sections do not cover completely separate questions; rather, the implied `big question' has been divided into logical subtopics.

Part II explains why stardates are so confusing, by describing some popular theories (and why they don't work). Part III follows its own narrative structure, and presents an investigation into stardates. Part IV describes the major implications of the system derived in part III. Part V presents a number of possible objections to the system, and refutes them.

IMPORTANT NOTE: if this version of this text is more than a month old, it may be out of date. See part VI for information on getting the latest version. You can contact the author by email at .


Note the following abbreviations, which will be used without further explanation:

FTB Federation Timebase
SD stardate

ST:TOS "Star Trek" (the original TV series)
ST:TAS "Star Trek" (the animated TV series)
ST:TNG "Star Trek: The Next Generation" (TV series)
ST:DS9 "Star Trek: Deep Space Nine" (TV series)
ST:VOY "Star Trek: Voyager" (TV series)
TCFS the classic film series (ST:TMP to STVI:TUC)

ST:TMP "Star Trek: The Motion Picture" (feature film)
STII:TWOK "Star Trek II: The Wrath of Khan" (feature film)
STIII:TSFS "Star Trek III: The Search for Spock" (feature film)
TVH:STIV "The Voyage Home: Star Trek IV" (feature film)
STV:TFF "Star Trek V: The Final Frontier" (feature film)
STVI:TUC "Star Trek VI: The Undiscovered Country" (feature film)
ST:G "Star Trek: Generations" (feature film)
ST:FC "Star Trek: First Contact" (feature film)



Originally, stardates were used so that Star Trek could be established as taking place a long way into the future without actually being pinned down to a particular time. The stardates were arbitrary, chosen without regard to consistency. The only thing that was consistent was that the stardates generally increased. However, because episodes got out of order in the production sequence, and were shown in a different order again, even this could not be relied upon from week to week.

Furthermore, even ignoring obvious verbal slips, the stardate ranges of episodes occasionally overlapped, and stardates sometimes even decreased within the confines of a single episode. When pressed for an explanation, Gene Roddenberry said:

This time system adjusts for shifts in relative time which occur due to the vessel's speed and space warp capability. It has little relationship to Earth's time as we know it. One hour aboard the U.S.S.Enterprise at different times may equal as little as three Earth hours. The stardates specified in the log entry must be computed against the speed of the vessel, the space warp, and its position within our galaxy, in order to give a meaningful reading.

Roddenberry went on to explain that stardates would be different in different parts of the galaxy at any one time. He admitted that he didn't really understand this, and would rather forget about the whole thing. And that was when there was only ST:TOS to consider.

Roddenberry's explanation does make some sense. It seems to suggest that stardates are completely subjective. This will be dealt with in the next section. Contradicting this, however, is the suggestion that position is relevant to the calculation. This part of his explanation, at least, must be discounted on the grounds of absurdity. His explanation is not canonical, so it may be treated like any other theory.


A common theory, picking up on part of Roddenberry's explanation, is that stardates are measured subjectively by each different starship. This means that relativistic time distortions, caused by travelling at impulse speeds, cause stardate rates to vary from an objective point of view.

Such a system would be useless across the Starfleet, because stardate X to the Enterprise would be stardate Y to the Potemkin, and stardate Z to the Sutherland. This situation is obviously not very helpful when arranging a rendezvous.

To be useful, stardates must be universal, and the computers will have to allow for time dilation. The computers available in the 20th century are capable of compensating for this effect, so it is certainly possible in the 23rd century.


Another theory is that stardates refer only to the ship's current mission, but increase at an objectively constant rate. This is an improvement over the previous theory, because different ships' stardates would differ by constant values only. This theory has also been used to give some very plausible relative dates for ST:TOS.

However, it doesn't account for the Earthbound use of stardates, or the demonstrated universality of stardates in ST:TNG. Furthermore, if each ship has its own subjective epoch, it seems most odd that all stardates would increase at the same rate. The only type of stardates that would be of any use would be those referring to a single standard timebase (i.e., the Federation Timebase), and having the same origin for everyone.

The constraint of universality makes matters a little complicated, because it means that the rate of increase of stardates is not totally constant. For example, the duration of the ST:TNG series is confirmed within itself to have lasted about seven years, during which time the stardate has increased almost 7000 units. This is irreconcilable with the fact that SD 5943.7 to SD 7411.4 was more than two years (ST:TMP).


It has been suggested in numerous places that stardates are actually Julian dates, as used by 20th century astronomers, modulo 10000. This would make each stardate unit exactly 24 hours. This works well at some points in Trek history. Unfortunately, it makes the `five-year mission' some thirteen years long.


It has been suggested, in jest, that stardates are actually hexadecimal, and that it is merely coincidence that only decimal digits have been heard so far. This is worth mentioning, in order to point out that this FAQ proceeds on the basis that all stardates are specified in decimal.

It is interesting to note, however, that the distribution of digits is far from uniform. A canonical stardate ending in ".8" is a real rarity, though not totally unknown. The distribution of single decimal digit fractional parts, according to the most up-to-date episode list I can get at the time of writing, is thus:

     Digit  Occurrences  Proportion
         0            8       2.34%
         1           54      15.79%
         2           73      21.34%
         3           58      16.96%
         4           48      14.04%
         5           34       9.94%
         6           17       4.97%
         7           28       8.19%
         8            6       1.75%
         9           16       4.68%
     Total          342     100.00%

It used to be widely stated that the first digit of ST:TNG stardates was 4 because it was set in the 24th century. Obviously, this idea can have no place in a proper theory, because it would make each century ten years long. It is, however, the way this digit was decided initially for ST:TNG. The Voyager episode "Basics, Part II" finally canonically laid this bit of bunkum to rest, when it announced a stardate of 50032.7, while remaining firmly in the 24th century (2373 to be precise).


Many people have noted that between ST:TOS and ST:TNG, as well as the stardate system being revised, the warp factor scale changed. The warp scale had previously had no upper bound on warp factors, but the new scale has a maximum of warp 10, which is defined as infinite speed. (See the Warp Speeds FAQ for futher information.) It has been suggested that both changes happened a the same time, possibly as the result of the same new knowledge about the nature of time, warp drive, and the interaction of the two.

However, it actually appears that the warp scale changed sometime during the classic film series, well before TNG stardates were used. Consequently the two changes can not have occurred at the same time.



This FAQ addresses the problem of what stardates mean. Of course, considering that stardates are merely a way to refer to points in time, any meaningful answer must refer to some other standard way to refer to time. The adage about standards is especially true here -- there are so many to choose from.

Ultimately, it is desired that stardates be related to a standard currently in use. For example, Greenwich Mean Time (GMT). This is defined as local mean time at the Royal Observatory in Greenwich, London. Local mean time is defined in terms of the observed noon on each day. Consequently, each day of GMT is a slightly different length, and not even an integral number of seconds. (Otherwise the second would vary in length from day to day, which would be even worse.) This is, therefore, in its strictest form, not a very good standard.

UTC (Universal Coordinated Time) is a better standard. The second is the unit of time defined by the SI, and can be regarded as having a fixed duration. Each day is exactly 86400 seconds, except for the occasional day of 86401 seconds used to keep in line with GMT (to within one second). To date there have been thirty such leap seconds, the most recent on 1995-12-31. Theoretically there may also be days of 86399 seconds, though there have not been any so far, and it is not anticipated that any will be needed. This is a better standard for specifying time, but still suffers from variable day lengths, which makes its handling awkward.

However, both GMT and UTC suffer from a more fundamental flaw: they depend on observations made from a single planet. If the planet is changed significantly, or is destroyed, then the time standard is meaningless. Furthermore, anyone in a different reference frame (i.e., anyone not on Terra) will disagree with Terrans about the order of certain events. This is a fundamental aspect of relativity.

Fortunately, Treknology provides a solution. For FTL travel to avoid violating causality, it has to take place in such a way that all FTL travellers have the same frame of reference. (Refer to Jason Hinson's "Relativity and FTL" FAQ for the explanation of all this.) The only standard timebase that could be considered universal would be one based in this frame of reference. It has been established numerous times in ST:TNG that there is a Federation Timebase, which presumably is arranged in just this way.

Thus it is established that stardates are linked to the FTB. But what about Terran calendars? Because this standard reference frame is currently unknown to Terran science, it can be conveniently assumed to be close to the reference frame of Terra. Because the relation to Terran time is only approximate, the choice of GMT or UTC is irrelevant, and the distinction will be ignored from here on.

This makes it possible to refer to points in time -- unambiguously -- using the Gregorian calendar, which is what will be done for the remainder of this FAQ. The Gregorian calendar is chosen because it is the most widely used on Terra. Furthermore, it will be assumed that every day is exactly 86400 seconds long.


Since there must be some basis for a system, the following will be assumed, in decreasing order of importance:

1. Nothing will be arbitrary, unless it is unavoidable. The idea is that anyone working from the same data, using the same principles, will come to the same conclusion.

2. Stardates occur in the `right' order. That is, the stardate will always increase numerically in the direction of advancing time. From time to time it will be necessary for the stardate to be reset to zero, but only on a finite set of occasions. On the principle that the system be as simple as possible, this set should be as small as possible.

3. Stardates will, in general, increase at a constant rate relative to the Federation Timebase. From time to time this rate may vary, but only on a finite set of occasions. On the principle that the system be as simple as possible, this set should be as small as possible.

4. Stardate rates will be round numbers relative to Terran phenomena such as days or years.

Given the above assumptions -- and working by the principle that the system should be as simple as possible -- what follows is the investigation of the stardate system. ST:TOS stardates will be discussed first; the ST:TNG stardates can be added to the system later (and relatively easily). Note: unless otherwise stated, all stardates specified are exact. As discussed in the previous section, Terran times given are necessarily approximate.

The system worked out below does not attempt to explain known writing errors. Just as Data's remark in "Encounter at Farpoint" ("Starfleet class of '78...") is commonly ignored, errors of stardate such as those in "Dark Page" are ignored here. Verbal bloopers are also ignored, naturally. Also, because of their irreconcilable inconsistency, stardates other than the main one for each episode must be ignored.


Going by the Star Trek Chronology, the first and last episodes are "The Corbomite Maneuver" (SD 1512.2; assumed to take place 300 years after it aired in September 2266) and "Turnabout Intruder" (SD 5928.5; early 2269).

This choice of episodes has some faults. "Turnabout Intruder" was the last episode aired, but the stardate of "All Our Yesterdays" was later (stardate 5943.7 against 5928.5). Under the principle that stardates occur in the right order, "All Our Yesterdays" must be taken as the end-point for the mission. (It makes little difference anyway, because the actual date is only conjecture.)

Similarly, there is room for dispute over which episode comes first. "The Corbomite Maneuver" (SD 1512.2) was first in regular production, but that doesn't necessarily mean anything. Similarly, "The Man Trap" (SD 1513.1), the first episode aired, is not a good starting point. "Where No Man Has Gone Before" (SD 1312.4) was first overall in both production and stardate, but is generally regarded as being quite distinct from the rest of the series. "Mudd's Women" (SD 1329.1) has the earliest stardate of the episodes in regular production, providing another possible starting point. However, the episode "Charlie X" (SD 1533.6) contains a clear reference to Terran dates, making all this arbitrariness unnecessary.

[Note: the Chronology lists the stardate of "The Man Trap" as 1513.1, but the Star Trek Compendium says 1531.1. I would appreciate it if someone could check with the episode itself, to confirm one date or the other.]

At one point in "Charlie X", Kirk states that it is Thanksgiving day on Earth. For those not familiar with American customs, Thanksgiving day is the fourth Thursday in November. Assuming Kirk was indeed referring to that same Thanksgiving day (which seems likely), and accepting the Chronology's calculation of year, this pins down the date of Kirk's statement to 2266-11-22. Let this be the day after the initial statement of the stardate for the episode, and the conclusion is reached that the episode started on 2266-11-21. This is only two months different from the Chronology's conjecture, and has the advantage of being almost completely non-arbitrary.


Stardate 1533.6 was sometime during 2266-11-21. According to the Chronology, the end of the series (SD 5943.7) was in early 2269. The is approximately 4400 units spanning two and a half years. A nice round number close to this rate is 5 units per day. (4.8 units/day -- 0.2u/hour -- is also within the possible range. It would be less plausible, however, because it relates to hours, which are purely a human invention, whereas days are a natural phenomenon.)

With this rate, to make things easier, it can be assumed that any exact multiple of 5 units is midnight. So the Thanksgiving day in question, 2266-11-22, runs from exactly SD 1535 to just before SD 1540. Therefore, SD 5940 is 00:00 on 2269-04-21 ("All Our Yesterdays" is on that day).

This rate puts "Where No Man Has Gone Before" in 2266, in contradiction to the speculative date in the Chronology. (This is not a problem, because there is no stronger evidence to back up that particular speculation.) It also set dates for a number of other events that the Chronology has assigned conjectural dates. It gives us a date of 2270-02-09 for ST:TMP, which is not acceptable. ST:TMP should occur in late 2271, to give Kirk time to have "not logged a single star hour in two and a half years". So the stardate rate must have changed at some stardate between 5943.7 and 7411.4.


Going by the Star Trek Chronology again, these dates may be useful. "Star Trek: The Motion Picture" (SD 7411.4) was in late 2271, at least 30 months after the end of the original TV series. "Star Trek III: The Search For Spock" (SD 8210.3) was in late 2285. "Star Trek VI: The Undiscovered Country" (SD 9521.6) was in 2293. These dates are conjectural, but they have a solid basis. They may be moved a little without contradicting anything other than the Chronology itself.

(By the way, ST:TMP really does have a stardate of 7411.4, despite the manuals that say 7412.6. One of the barely-audible messages at the Epsilon 9 station mentions a rendezvous between two Federation ships to take place on stardate 7411.4. If you listen carefully it is also possible to make out the ships' names and registry numbers -- scout Columbia NCC-621 and scout Revere NCC-595. These names and numbers match those in the list of scouts in the "Star Fleet Technical Manual".)

TVH:STIV is about 3 months after STIII:TSFS according to Captain Kirk's log, but this reference can be ignored because he may have meant Vulcan months.


It turns out that the stardate rate has to change sometime between ST:TMP and STII:TWOK, as well as sometime before ST:TMP. The details of that period, encompassing ST:TMP, can't be calculated until this bit, for the remainder of the classic films, has been done.

The reference points to use for this are STIII:TSFS (SD 8210.3; late 2285) and STVI:TUC (SD 9521.6; conjectured to be 2293). The gap is 1311.3 units, covering 7-8 years. A suitable rate is 0.5 units per day. (0.48u/d -- 0.02u/hour -- is also within the possible range.)

Similarly to the first period of stardates, it can be assumed that any exact multiple of 0.5 units is midnight. This means that the days on which STIII:TSFS and STVI:TUC start will start at stardates 8210.0 and 9521.5 respectively. The calculation of exactly which dates these are must wait until the details of the intermediate stardate rate have been calculated.


Neither of the periods of stardates discussed above gives a satisfactory date for ST:TMP. It is therefore necessary to have an intermediate period of stardates to link the two. It is possible to make this link with a single intermediate period. This period must use up stardates much more slowly than either of the adjacent periods.

This intermediate period can have a rate of about 0.156u/d at the most. To have a rate any higher, this period would have to extend into ST:TOS or beyond STII:TWOK. It would be possible to use a rate of 0.15u/d (which has the advantage of making a standard 8-hour shift exactly 0.05 units long), but this makes the day length messy. (3u/d or 0.3u/d would be more manageable, but it isn't possible in this case.) The most logical rate to use is 0.1u/d.

Now to place ST:TMP... It must be a fair bit more than 30 months after "All Our Yesterdays", ideally in late 2271. To make the changeover point from ST:TOS stardates to this period an exact midnight -- it would be madness to do otherwise -- it must be a multiple of 5 units. This means that moving it one day forward or back changes the date of ST:TMP by 49 days, because the stardate rates differ by a factor of 50. The most reasonable date possible for ST:TMP under this limitation is 2272-01-10, with the changeover at SD 7340.0 (2270-01-26). This is not quite in 2271, but close enough not to cause problems with later dates.

And for the second changeover... It turns out that fairly sensible dates for STIII:TSFS and STVI:TUC can be obtained by putting the second changeover at SD 7840.0 (2283-10-05) -- exactly 5000 days (500 units) after the first changeover. This makes it all look designed. This puts STIII:TSFS at 2285-10-14, consistent with the Chronology. It also makes STVI:TUC 2292-12-19, which is not quite the conjectural 2293, but is close enough.


Throughout ST:TNG stardates have increased at approximately 1000 units per year. (In fact, during ST:TNG, the second digit of the stardate indicated the season.) From these facts, the Chronology has conjectured that ST:TNG stardates increase at exactly 1000 units per year. Numerous references within the series supports this conjecture. Of course, they support it because the shows were written with that system in mind. It would be difficult to contradict this.

However, there are a few inconsistencies in this respect within the series. In "Eye of the Beholder" (ST:TNG, SD 47622.1; incidentally, this is the second of (so far) three very near title clashes in Star Trek -- there was an animated Star Trek episode called "The Eye of the Beholder") an incident at Utopia Planitia is referred to both as stardate 40987 and as eight years ago; allowing for rounding, this gives a year length of between 704.4 and 954.4 units. In "The Pegasus" (ST:TNG, SD 47457.1), the disappearance of the Pegasus was stardate 36764 and twelve years ago; this gives a range of 807.8 to 974.4 units per year. In "Second Sight" (ST:DS9, 47329.4), the battle of Wolf 359 (SD approximately 44002) was exactly four years ago, giving a year length of 832 to 834.75 units.

There are some other references consistent with an 833 unit year, but most are not so clearly referring to Terran years. In any case, the vast majority of references support 1000 units per year, leaving these other references as isolated mistakes.

In "The Neutral Zone" (SD 41986.0), Data stated that the year was 2364. This almost solves the problem of year calculations. The only problem is that Data did not go on to say exactly what day of the year it was, so there is an uncertainty of one year when calculating dates from this.


Note that ST:TNG stardates have five digits before the decimal point, where ST:TOS stardates have four. This would seem to suggest a change of outlook on the part of the Federation, from short-term to long-term. This coincides with the change from stardate units being convenient fractions of Terran days to being a convenient fraction of a year. Also, the length of stardates in ST:TOS could allow for up to about 5.4 years before needing to be reset to zero, whereas the ST:TNG stardates only need to be reset once a century. (Presumably one often needed to specify which period of 5.4 years one meant by a particular stardate.)

The Chronology proceeds under the assumption that all first season stardates were in the year 2364, and then all second season in 2365, and so on. There isn't really any evidence to support this, but it makes things neat. The production crew have occasionally calculated exact dates on this basis. In order to keep things simple, it will be assumed that this is how the stardates actually work. This makes stardate 00000.0 midnight at the beginning of 2323-01-01.

Stardate 99999.9 should be about 50 minutes before midnight on 2422-12-31, after which the stardates get reset to zero again. However, it is not possible to state this as being exact, because not all centuries are the same length. Every fourth century contains 25 leap years; the rest have 24 each. The difference in the lengths of individual years creates a more immediate problem: the 1000s of units can't match up exactly with calendar years.

Obviously, one solution would be for the stardate rate to vary from year to year, making each year 1000 units whether it is 365 or 366 days long. This is not acceptable as a universal time system, however. The rate changing every fourth Terran year makes things difficult for the Vulcans, and the Andorains, and in fact almost every member of the Federation.

So the rate must make 1000 units fit a mean solar year of 365.2425 days exactly. (Actually that's not quite exact, but that is the exact mean length of a year by the Gregorian calendar. This is more appropriate, because the Gregorian calendar is being used to specify dates.) 400 years is exactly 146097 days, no matter which 400 years one counts. By a happy coincidence, this is exactly 20871 weeks. (This fact is of no practical use, except in the construction of perpetual calendars.)

For convenience, it can be conjectured that starships on extended voyages -- and maybe some civilians too -- use a standard year of length 365.2425 days. This doesn't mean they add on an extra 5.82 hours at the end of the year, but that they distribute it evenly throughout the year. This makes each day about 57.4 seconds longer than 24 hours. In fact, to make chronometers visually indistinguishable from those previously in use, the second would get longer.

This standard year is exactly 31556952 SI seconds long, but is internally divided into the usual 31536000 seconds. This makes the `chronological second' approximately 1.00066 SI seconds, and even Data would have difficulty distinguishing the two.

The two calendar styles could coexist quite easily, because they would rarely be more than a few hours different. In order for them to coexist over a long period of time, they must agree on what day of the week any particular date falls on. (A consequence of this is that existing perpetual calendars will still be applicable to the new calendar.) Where there would be a leap day in the old-style Gregorian calendar, there is merely a jump in the day of the week. For example, Wednesday 2396-02-28 would be followed by Friday 2396-03-01, missing out Thursday 2396-02-29 which would appear in the Gregorian calendar.

This new calendar will hereafter be called the "quad-cent calendar". It comes exactly into line with the old-style calendar every 400 years. Since the origin for ST:TNG stardates is 2323-01-01, that must be when the two calendars match up. (The next time will be 2723-01-01.) Hereafter, quad-cent calendar dates will be written like 2323*01*01, instead of 2323-01-01.


SD 9521.5 corresponds to the date 2292-12-19. The digits run out and are reset to zero on 2295-08-03. This starts a special `issue' of stardates, whose sole purpose is to bridge the gap to 2323-01-01, when the new-style stardates take over. In this new issue, SD 5000.0 is 2322-12-20, almost exactly 30 years after STVI:TUC. This makes 2323-01-01 SD 5006.0. So stardate 5006.0 in that issue became stardate 00000.0, and the date, 2323-01-01, became 2323*01*01 for the purposes of stardates.

If Thanksgiving were twelve days later, these numbers would be unbelievably neat. So neat, in fact, that one might well reach the conclusion that this system was actually designed to work this way.


From the ST:TOS stardates we know that SD 1530 is 2266-11-21. Extending this back, SD 0000 is 2266-01-19, well after the beginning of the five-year mission. To go further back, we must go into an earlier issue of stardates. In this earlier issue, SD 9995 must be 2266-01-18 (one day before the ST:TOS stardate 0000). This makes SD 0000 in this issue 2260-07-29. Continuing this process backward, it should be possible to find a sensible starting point for all stardates.

The theory is here supported by the ST:DS9 episode "Equilibrium", which puts Joran Bella's birthdate at stardate 0024.7, and notes that this is in 2260. (This theory makes it 2260-08-02.) However, the same episode puts his death as stardate 8615.2 and 2286. This is not quite consistent with this theory, being two years out.

None of the major real-life space events is a 0000. The 43rd issue before the classic series has its 0000 on 2030-08-04, and 2030 is supposed to be the year of Zefram Cochrane's birth; this is a rather implausible candidate for the origin. The 37th issue before the classic series has its 0000 on 2063-06-12, just a couple of months after Cochrane's first demonstration of warp drive (2063-04-05, according to ST:FC). I think the powers that be here missed a great opportunity here. It looks like stardates just aren't based on any significant event in space travel.

The 19th issue before the ST:TOS stardates has its SD 0000 on 2162-01-04, which is tantalisingly close to 2161 (Federation incorporation). Taking this as the origin of stardates, it could mean that Starfleet originally used old-style Terran dates, but found them inappropriate for deep-space use. A few months after incorporation, then, they started up stardates.

If we call these first stardates `zeroth-issue', which will be written like [0]0000, ST:TOS uses 19th-issue stardates (e.g., [19]1530 is 2266-11-21). The partial issue to link the TCFS stardates with the ST:TNG stardates is the 20th issue, and ST:TNG stardates are 21st issue. This notation provides a convenient way to refer to stardates a long way from the current time.



Before the Federation was founded, everyone involved in space travel used their own time system. Terrans used the Gregorian calendar and UTC; Vulcans used their own calendar. Initially the Federation used the Terran calendar, just as it used the Terran language and had its headquarters on Earth. This system proved to be extremely unpopular, especially with the Vulcans, who liked a calendar to have some logic about it. (Alternating 30-day months with 31 is fine, but sticking a 28 in the middle of that lot is just silly.)

Starfleet bureaucrats quickly devised a compromise system -- which didn't match anyone's calendar. Midnight on 2162-01-04 (only a few months after the incorporation of the Federation) was arbitrarily declared to be stardate zero, and stardates increased at the arbitrary rate of five units per Terran day. This recognised the importance of Terra to the Federation, but also allowed anyone to convert stardates to their own calendar by simple mathematical formulae.

The system having been cobbled together in a rush, the numbers became unmanageable fairly soon. What would have been stardate 10000 (midnight on 2167-06-27) was made stardate 0000 again. The first group of stardates could be referred to, when necessary, as zeroth-issue stardates, such as [0]1234, and the new issue as first-issue stardates, such as [1]1234. This reset to zero continued to occur every five and a half years, until 2266, when the 19th issue of stardates started. The Federation now having survived a little over a century, referral to stardates several issues ago was becoming increasingly common. That year, Starfleet put together a committee to investigate what type of stardate system would be more acceptable.

The committee's report, in 2267, recommended that the stardate rate be slowed to 0.1 units per day. This would make the same number of digits as had been previously used, and had covered five and a half years, cover two and a half centuries. It was decided that this system should be field-tested between stardates [19]7340 and [19]7840 -- 500 units, 5000 days. So from 2270-01-26 to 2283-10-05 this system was used. It proved to be unpopular, because one always had to specify an extra digit after the decimal point in order to get the sort of precision one had had with the older stardates. Terrans who had grown accustomed to the five-per-day rate found it difficult to adjust.

As a result, it was decided in 2280 that at the end of the test period (SD [19]7840) the new rate should not continue. Instead, a 0.5 units per day rate would be used, which would solve the main problems of both earlier systems. Four digits (before the decimal point) would last more than fifty years; it would rarely be necessary to use extra digits; and the five-per-day rate would be preserved. (Five of a different digit, but still five.) This system was used from stardate [19]7840, and was intended to be a permanent change.

With the length of starships' missions continually increasing, it started to look rather comic for starships to keep in time with the daily cycle of a planet they would sometimes have no contact with for years at a time. Keeping to its yearly cycle still had some logic, but keeping to a 24-hour day as well -- which necessitated the use of leap days -- was just silly. In 2318, over 150 years after the incorporation of the Federation, it was decided that starships should start to use a rationalised calendar, which would keep the years the right length but make the day slightly longer.

In keeping with this longer-term view of time, the stardates would be increased to five digits, and the rate changed to match this new rationalised year. A rate of 1000 units per mean year would be convenient. This would make it impossible to instantly work out the time of day from the stardate, but Terrans tend to prefer the traditional hours, minutes and seconds for specifying times anyway.

What would have been stardate [20]5006.0 -- midnight on 2323-01-01 -- became stardate [21]00000. At the same time, all Earth ships switched to the new-style calendar, and the stardate rate was changed to match it. This system has remained in use up to the present (SD [21]51000, 2374*01*01).


Here's when the classic movies are set:

Star Trek: The Motion Picture 7411.4 2272-01-10
Star Trek II: The Wrath of Kahn 8130.3 2285-05-07
Star Trek III: The Search For Spock 8210.3 2285-10-14
The Voyage Home: Star Trek IV 8390 2286-10-09
Star Trek V: The Final Frontier 8454.1 2287-02-14
Star Trek VI: The Undiscovered Country 9521.6 2292-12-19

Helpfully, STV:TFF occurs in 2287, as the Chronology conjectures. These dates make Vulcan months about four times as long as Terran ones. Kirk's birthday (STII:TWOK) is the 7th of May. (The 22nd of March, conjectured in the Chronology, is taken from William Shatner's birthday.) "The Deadly Years" (SD 3478.2) was 2267-12-15, and Kirk was 34 then, which means that his birthdate must be 2233-05-07. The year is consistent with the Chronology.

In ST:TNG, date calculations are much easier, because of the 1000 units per year rate and the quad-cent calendar. The year can be obtained from the first two digits, and the day from the rest -- there is no need to consider leap years. Here are a few significant dates:

Enterprise-D commissioned 40759.5 2363*10*05
Encounter at Farpoint 41153.7 2364*02*26
Datalore 41242.4 2364*03*30
Skin of Evil 41601.3 2364*08*08
Future Imperfect 44286.5 2367*04*15
Emissary (ST:DS9) 46379.1 2369*05*19
Descent, Part II 47025.4 2370*01*10
Parallels 47391.2 2370*05*23
Caretaker (ST:VOY) 48315.6 2371*04*26
Star Trek: Generations 48632.4 2371*08*19
Enterprise-D destroyed 48650.1 2371*08*26
The Way of the Warrior (ST:DS9) 49011.4 2372*01*05
Enterprise-E launched 49027.5 2372*01*11
Star Trek: First Contact 50893.5 2373*11*23

The commissioning date of the Enterprise bears a suspicious resemblance to the launch date of Sputnik I (1957-10-04). This is designed; in fact the Enterprise date was supposed to be 2363*10*04, but a mistake was made. There is a trap when calculating these dates that would make any stardate appear to represent a date one day earlier than it should. It would appear that Sternbach and Okuda fell right in it.

The "Future Imperfect" date is Riker's birthday; his 32nd according to the Chronology (the Chronology lists a birth year of 2335, but no date). "Parallels" is Worf's birthday. Using the "Datalore" and "Descent, Part II" stardates, Lore's lifespan can be calculated at 5 years, 286 days.

The Organian peace treaty between the UFP and the Klingon Empire lasted from SD [19]3198.4 ("Errand of Mercy", ST:TOS) to [21]49011.4 ("The Way of the Warrior", ST:DS9). This is a little over 104 years, from October 2267 to January 2372.

There is a slight problem with some of the ST:TNG first season stardates. "The Battle" (SD 41723.9), "The Big Goodbye" (SD 41997.7), "Angel One" (SD 41636.9) and "The Arsenal of Freedom" (SD 41798.2) all have stardates after "Skin of Evil" (SD 41601.3), but show Tasha Yar alive. It seems that the production crew learnt from this, because they have kept stardates in order ever since. To make these stardates make sense, we must assume them to be slips of the captain's tongue. (More obvious verbal errors were made in "The Deadly Years", "Datalore" and "Birthright, Part II".)

Data stated in ST:FC that he had not used his "multiple techniques" for "8 years, 7 months, 16 days, 4 minutes, 22 [seconds]". That would be a date of approximately 2365*04*07, or a stardate of approximately 42263.4. This is early second season, between episodes, well after Yar's death and well before "In Theory" -- an as-yet unrevealed lover.


It has been calculated that stardates begin on 2162-01-04. It is quite possible, of course, to continue stardates back in time from that point, using negative issue numbers. Within each issue the stardates will still increase in the direction of advancing time; only the issue numbers will be unusual.

To start with, midnight on 2162-01-04 is stardate [0]0000. This means that midnight on 2162-01-03 can be referred to as stardate [-1]9995. SD [-1]0000, consequently, was 2156-07-14. The fact that stardates were not actually in official use at that time is irrelevant.

It seems possible that negative-issue stardates are used in the 23rd century to refer to events prior to 2162. When going as far back as the 20th century, though, the old-style Gregorian calendar has always been used by the crew of the Enterprise. In fact, they have never been canonically observed to use stardates to refer to any time earlier than 2260. Of particular interest is the final log entry in ST:FC: "Captain's log, April 5th, 2063...", indicating that in official contexts stardates are not used for dates that early, or at least are not universally used.

It is possible to continue stardates back to the 20th century, but the issue numbers get sufficiently large (in the negative direction) to be awkward. This table shows the issue origins for the next few years:

[-36]0000 1964-11-18 [-24]0000 2030-08-04 [-12]0000 2096-04-19
[-35]0000 1970-05-11 [-23]0000 2036-01-25 [-11]0000 2101-10-11
[-34]0000 1975-11-01 [-22]0000 2041-07-17 [-10]0000 2107-04-03
[-33]0000 1981-04-23 [-21]0000 2047-01-07 [-9]0000 2112-09-23
[-32]0000 1986-10-14 [-20]0000 2052-06-29 [-8]0000 2118-03-16
[-31]0000 1992-04-05 [-19]0000 2057-12-20 [-7]0000 2123-09-06
[-30]0000 1997-09-26 [-18]0000 2063-06-12 [-6]0000 2129-02-26
[-29]0000 2003-03-19 [-17]0000 2068-12-02 [-5]0000 2134-08-19
[-28]0000 2008-09-08 [-16]0000 2074-05-25 [-4]0000 2140-02-09
[-27]0000 2014-03-01 [-15]0000 2079-11-15 [-3]0000 2145-08-01
[-26]0000 2019-08-22 [-14]0000 2085-05-07 [-2]0000 2151-01-22
[-25]0000 2025-02-11 [-13]0000 2090-10-28 [-1]0000 2156-07-14

Looking at today's date, 1994-05-23 is SD [-31]3890. Right now, 12:43pm UTC, is SD [-31]3892.64. The first episode of Star Trek aired on stardate [-36]3300.31.



Objection: this stardate system makes stardates round numbers of Terran days, but the Klingons and Romulans and so on wouldn't use such a system.

We've never seen Romulans use a stardate. In fact, the only occasion when a non-Federation person used a stardate was in the seventh season ST:TNG episode "Liaisons". In that episode, an alien was trying to imitate a Federation civilian. He had obtained logs from a crashed Federation ship, and had also had some official contact with the Federation. So it seems clear that stardates are a Federation invention, but their use is not limited to Starfleet.


Objection: this system has stardates starting at zero, but there hasn't been any canonical stardate below 1000.

This is a valid objection. There is really no evidence either way, so it was decided that stardates would do what it looks like they ought to. The rationale is that stardates will be handled primarily by computers, and computers like to start counting at zero. Zero-based counting actually makes a lot more sense than one-based counting, so now that we have the concept it makes sense that a new time standard will use it.


Objection: the 4 at the beginning of TNG stardates is supposed to represent the 24th century. This means that one year has to be 100 units, not 1000.

Or: the digit after the first 4 is the season number, so what happens when they get to season 10? Does the stardate become 410xxx?

The 4 at the beginning of TNG stardates was originally (in real life) decided on for two reasons. First, it showed that TNG was a lot later than the films and the original series. Second, 4 was chosen specifically because TNG supposedly took place in the 24th century. This does *not* mean that that is the Star Trek universe's reason for the 4. 4 just happened to come up shortly before the Enterprise-D was launched.

The second digit was originally chosen to correspond to season numbers, but that doesn't mean that it will always be like that. It was merely a convenience, which still works (albeit in a modified form) for ST:DS9 and ST:VOY. We have now reached what would have been ST:TNG's tenth season, and the stardates are of the form 50xxx. This does not mean that they have reached the 25th century. (2401*01*01 will be SD [21]78000. And no, the 25th century will *not* start in 2400. And 2400 *will* be a leap year in the Gregorian calendar.)


Objection: in the fourth season ST:TNG episode "Family", Picard visits his family in Labarre, France, Terra. This being stardate [21]44012.3, this theory makes the date 2367*01*05, which should be winter in that part of the world. In the episode it was very clearly not winter.

This is a strong objection. In fact, it seems likely that the writers simply made a mistake -- the production team worked on the basis of stardates divisible by 1000 being the beginning of the year, though they never got that information onto the screen. This system assumed that that was the case primarily for simplicity. Other things being equal, this consideration would be overridden by the on-screen evidence. However, in this case other things are not equal.

In TVH:STIV (stardate [19]8390, 2286-10-09), the `Whalesong' probe visited Terra. It was observed to cause severe atmospheric disturbance at the time. It has been conjectured that it had more severe climatic effects than were readily apparent. The novel "Probe" (entirely non-canonical, of course) sets out some of these ideas. (It's also a good novel.) It is conceivable that the effects of the probe included a shift in Terra's orbit, or permanent climatic change, such that in January 2367 the atmospheric conditions in France resembled a 20th century summer.

This does seem a little far-fetched, and requires justification. The only other way to avoid this problem is to have stardate issue 21 start in the middle of 2322, instead of at the beginning of 2323. This would mean that the change to the new system would occur sometime around SD [20]4930. That is no neater than SD [20]5006.0, so there would be no reason at the time to use it. (The use of SD [20]5006.0 is justified only by the fact that it is the beginning of a year.)

Another suggested explanation is that the Earth's weather modification system -- mentioned in the TNG epiode "True Q", and hinted at in TVH:STIV -- was used to change the climate in France deliberately. The ST:TNG episode "Sub Rosa" supports this hypothesis, by confirming that Federation technology would be sufficiently powerful to do this. It seems unlikely, though, that the UFP would want to make such a major change to the climate. This must also be taken into consideration when evaluating the "Probe" explanation above -- why wasn't the weather modification system used to repair the climate after the probe changed it? It is possible that the weather modification system is not capable of making such major changes.

If you do the calculation, you will find that allowing the 20th issue of stardates to continue to its natural end before starting the 21st issue would put "Family" in mid-May. Unfortunately, it would be May of 2394, so that idea must be discarded.

Intriguingly, a correspondent notes other time evidence in the episode. At the end of the episode, we see Rene outside, and observe a shooting star passing the constellation of Orion. Orion is, of course, only visible in the northern hemisphere during winter, further substantiating the January date. This seems to support the deliberate weather modification theory.


Objection: in the seventh season ST:TNG episode "The Pegasus", stardate 47457.1, Riker stated that he had had his beard for four years. If 1000 units is one year then he'd had it for at least five years.

During season one, he was clean shaven. The beard first appeared in season two (earliest known stardate 42073.1), but was not fully grown. (It had to be kept slightly short for the entire season for continuity purposes.) From the beginning of season three, stardate 43125.8, the beard has been fully grown.

It is possible that Riker was referring to the fully grown beard, which he had had less than five years.


Objection: in the ST:TOS episode "Journey to Babel", SD [19]3842.3 (2268-02-26), Sarek states that he is 102.437 years old. In "Sarek", SD [21]43917.400000 (2366-12-01), he is said to be 202 years old. That is an age difference of 100 years, but the episodes took place 98 years apart.

It is possible -- in fact, very likely -- that these are references to Vulcan, not Terran, years. As it is entirely possible that only one (most likely the second) age reference is in Vulcan years, it is not possible to reliably determine the length of the Vulcan year from these data.

There is another possibility. As the discrepancy is only two years in a hundred, it is conceivable that one or both references were to Sarek's subjective age, with the discrepancy accounted for by relativistic effects.


Objection: in the second season ST:DS9 episode "Second Sight" (stardate 47329.4), Sisko states that it is the fourth anniversary of his wife's death. From "Emissary" it is known that Jennifer Sisko died in the battle of Wolf 359. That was sometime between the starts of the fourth season ST:TNG episodes "The Best of Both Worlds, Part II" (SD 44001.4) and "Family" (SD 44012.3). This dating information makes four years something between 3328 and 3339 units, and one year something in the range 832 to 834.75 units. This is incompatible with the notion that 1000 units is a year.

The real reason is (probably) that the writers made a mistake. An isolated case like this might normally be ignored, but in this case there is an explanation.

It has been established that Deep Space Nine works to Bajoran time, with 26 hours per day. It seems logical to extend this to years, in which case Sisko may have been referring to Bajoran, not Terran, years. This explanation has the helpful consequence that we now know a Bajoran year to be about 304 Terran days long. One might also conclude that a Bajoran year is also (usually) 281 Bajoran days long, but that conclusion relies upon Bajoran hours being the same length as Terran hours.


Objection: in the fourth season ST:DS9 episode "Starship Down" (stardate 49263.8), Major Kira states that it is an anniversary of the arrival of the Emissary (Sisko). Sisko arrived in "Emissary", stardate 46379.1. The difference, 2884.7 units, is incompatible with the Bajoran year length calculated in section V.6, around 833 units.

Once again, the writers simply ignored precedent when adding this minor subplot to the episode. There is no way to reconcile the problem, as stated above, with the other known data concerning Bajoran time. The best explanation available is that the anniversary was not of Sisko's actual arrival on DS9, but of some event that took place shortly after that.

Given the Bajoran year length of between 832 and 834.75 units, calculated in section V.7, the date in question must include some stardate between 46759.5 and 46767.8. This is approximately in the middle of the first season of DS9. There is no known event at that point in the first season that might be given this kind of significance, but that doesn't mean there wasn't one.


Objection: in the seventh season ST:TNG episode "Dark Page" (SD 47254.1), Lwaxana Troi's personal log entries for stardates in the 30000s were seen. These were described without hesitation as being from 35 years previous. This makes each year about 500 units. Of course, these could have been Betazoid years.

The Revised Chronology explains that the correct stardates -- around 05000 for the dates 42 years ago -- would have risked confusion with ST:TOS stardates. They therefore ignored the logical system, and caused even more confusion.



This FAQ is posted to the USENET newsgroup rec.arts.startrek.tech every 30 days. It is cross-posted to rec.answers and news.answers. It can be found by searching any of these newsgroups for the subject line "Stardates in Star Trek Mini-FAQ" (without the quotes). Depending on the configuration at your site, it is possible that it may be expired earlier than intended, and therefore not be available.

It is also available for anonymous FTP from rtfm.mit.edu ( as file /pub/usenet/news.answers/star-trek/stardates. This will contain the last version to be distributed via USENET. rtfm.mit.edu also has a number of mirrors, in which it is archived as star-trek/stardates. These URLs point to a selection of mirrors around the world -- pick the one closest to you:

If you do not have access to FTP, you can obtain a copy from rtfm.mit.edu by email. To do so, send an email message to containing the line:

send usenet/news.answers/star-trek/stardates

As a last resort, you can obtain the latest version direct from the author by email. To do so, send an email message to , with the subject line "send stardates". Messages for the attention of the author should be sent to the same address, using some other subject line.


The canonical version of this FAQ will always be the plain ASCII text version, as posted to USENET. Conversions to other formats may become available from time to time, however.

An HTML version can be found at Joseph Creighton's Star Trek web page, . (At the time of writing this is actually an encapsulation of the ASCII version, but it should become a proper HTML conversion soon.)


A stardate calculation computer program is available. To get the program in the form of a compressed `tar' archive, send email to with the subject line "send stardates.tar.gz". To get the program as a DOS zip file, use the subject line "send stardates.zip", and to get a Unix shell archive use the subject line "send stardates.shar".


Comments on this FAQ are always welcome. Send email to . PGP encrypted mail is welcome: the author's PGP public key may be obtained from any of the PGP public key servers, and the key fingerprint confirmed by fingering his address.


Major thanks to Jason Hinson , for writing the Relativity and FTL FAQ. (That document is recommended reading for all Treknologists.)

Credits go to the following people on the Internet, either for interesting USENET postings or for helpful email messages:

Dewitte A. Baisch, Jr
Greg Berigan
Joseph Chen
Ted Clancy
Edgar Governo
Scott F. Ichniowski
Joseph M. Osborne
Steve Pugh
Boris Skrbic
Michael M. Welch

Version 0.*
Pre-release versions. Mostly consisted of a few thousand digits on a lot of paper.

Version 1.0 (1994-05-23, SD [-31]3892.64, 400 lines, 21kB)
The initial release version. This version is in the public domain.

Version 1.1 (1994-11-05, SD [-31]4723.71, 449 lines, 23kB)
Minor changes were made to clean up small sections. Section numbering, a table of contents, and the history section were added. This version was the first to be posted to the USENET newsgroup rec.arts.startrek.tech, and is in the public domain.

Version 1.2 (1994-12-05, SD [-31]4872.95, 709 lines, 36kB)
A fairly extensive revision, including a rewrite of almost all of the text. The introductory sections were slightly rearranged, and the main investigative sections were renamed to be more consistent. New sections were a detailed description of 20th century stardates and a C program to calculate contemporary stardates. The document became a FAQ.

Version 1.3 (1995-01-08, SD [-31]5042.92, 883 lines, 43kB)
An intermediate release. The previous flat numbering scheme was changed to a two-layer hierarchical system, making the document easier to use. A new section on time standards was added, and the section on other stardate theories was expanded to become a major division.

Version 1.4 (1995-04-19, SD [-31]5547.00, 1782 lines, 77kB)
A new part was added to the document, detailing and explaining away some objections to the theory. The stardate program was improved and moved to a new part, and another related program was added. An error in the original calculation was discovered while testing the new stardates program: the 20th-issue stardate for 2323-01-01 was previously given as [20]5006.5, whereas it is actually [20]5006.0. This change does not have any significant effects.

Version 1.5 (1996-03-28, SD [-31]7269.00, 1139 lines, 57kB)
A revision of the previous version. The only major change is that the stardate calculation programs added in the previous version are now distributed separately. (They took up a lot of room, and seemed out of place in a textual document.) Parts of the text have been reworded, and some minor sections have been added.

Version 1.6 (1997-02-09, SD [-31]8857.62, 1199 lines, 61kB)
A revision of the previous version. A few new points of information are added. Some dates from ST:FC are used. We have also finally passed stardate 50000 in the current episodes. The major change is the redesigned stardate program, in the addendum (now available in several formats).

A plain-text version of this FAQ, along with the program files, is also available.

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