This evolving document originated long before Mike and Denise Okuda's Star Trek Chronology was published. Most dates are in very close agreement, however to avoid copyright infringement, no effort has been made to make this document conform with the Okuda's, other than as a result of subsequent information presented on-screen.

Many subjective decisions had to be made in aligning the entries of this timeline. Vague dates were defined as specific years where possible. Many dates had to be inferred. In some cases, I have applied my own interpretation to statements made on screen for which there is no "proof."  As such, your mileage may vary.

This timeline assumes that for the television series, one season equals one year. This assumption is supported by the TNG fourth season episode Data's Day, in which Data says that 1,500 days have passed since the commissioning of the Enterprise, which equals 4 years, 40 days. It was fairly clear that the ship was brand new in Encounter at Farpoint. 

Unless evidence is given otherwise, this timeline assumes that people enter the Starfleet Academy at age 18 and graduate 4 years later. It follows the schedule of rank advancement which Data told his brother Lore: 2 years as an Ensign followed by ten years as Lieutenant (JG) and Lieutenant. Duration as a Lieutenant Commander, Commander and Captain is a much more of a grey area, and is based on what is known about the individual. I have often taken a rank and extrapolated backward to get a birth year. I also postulate that some officers return to the Academy when they become a Lieutenant for advanced command training. This explains why Lieutenant Saavik was among cadets in ST2, and also fits with various other dates.

Some dates and events in this timeline are pure conjecture on my part. While I feel they are consistent with the stated facts, they are very open to later contradiction. 

Fans of other works of Gene Roddenberry will note that the Questor story premise is included in this timeline, since the end of this android's life span happens shortly after the creation of the United Federation of Planets, as dated in The Outcast. My date for the birth of Surak is much later that postulated by Diane Duane in her excellent novel Spock's World. I feel that Vulcans would have made much more technological progress if they had turned to logic thousands of years ago. Similarly, the date for Kahless' coup that created the Klingon Empire is pure guesswork. 

Few Star Trek dates are known definitively, but those that ARE known are a key to the remaining organization of this timeline.

1. The first episode of Star Trek Discovery was given as May 11, 2256.
2. In The Neutral Zone, Data said it was the year 2364. Combine that with the "78 years have passed" statement from the beginning of Encounter at Farpoint, and you get 2285-86 for ST2-5. (Encounter at Farpoint was produced between ST3 and ST4.) 
3. In Sarek, the ambassador's age was given as 202, whereas in Journey to Babel it was given as 102 years old, meaning the second year of TOS was 2266. These are assumed to be Federation standard years. 
4. The remark from ST3 that the Enterprise is 20 years old is considered incorrect in this timeline because is it inconsistent with points 2 and 3 above. However it HAD been close to 20 years since Kirk first set foot on the Enterprise. Maybe that's what the Admiral meant, but didn't express too well. 
5. I place the second TOS pilot, Where No Man Has Gone Before in 2264, with the remainder of season one in 2265, to account for the slight design differences seen on the Enterprise after that episode. Since Mark Piper is Chief Medical Officer of the ship in that episode, I conclude that McCoy joined the crew in that early 2265 time frame. 
6. ST1 is set in 2272 as a reasonable time for a major refit of the Enterprise, three years (called The Lost Years by Pocket Books) after the end of it's five year voyage under Kirk. I sometimes think of the years between ST1 and 2 as "The Other Lost Years." More Lost Years now must be set in the years between ST5 and 6, and of course "The Undiscovered Country" after ST6. 
7. I place ST6 in 2293 because: In Reunion, Geordi said Klingons and Romulans had been blood enemies for 75 years. TNG season four is 2367, minus 75 years gives about 2293. They did NOT appear to be blood enemies yet in ST6. McCoy said he had been CMO of the Enterprise for 27 years. Mark Piper was CMO in Where No Man Has Gone Before, meaning McCoy transferred to the Enterprise in 2265. 2265 plus 27 is 2292 or 93. 2293 would also be about the end of a five year voyage beginning in 2287, somewhat after the Sybok incident. Scotty had been in the USS Jenolen transporter pattern buffer for about 75 years. Based on 2369 for TNG season six, this gives 2295-6 for his disappearance, making 2296 the absolute latest ST6 could have happened. 
8. Similar to TOS, I place the TNG pilot, Encounter at Farpoint, in the year before season one, although I expect little time passed between EAF and the remainder of season one. 
9. The date of the Khitomer massacre is only given by Picard as a vague "20 years ago," but calculating Worf's age backward from the date of his promotion from Lieutenant (JG) to full Lieutenant, as outlined above, and given his statement from Heart of Glory that he was 6 when the attack occurred, the result is exactly 20 years before Sins of the Father. As a result, in TNG season 1 Worf is 23, and in DSN season 4, Worf is 32.
10. In episode 1 of Discovery, the year is clearly identified as 2256.  

1992 marked the date given in TOS for the beginning of the Eugenics Wars, from 1992 to 1996. As Spock described it, a group of supermen who are the product of "selective breeding," (later modified in ST2 to be "genetic engineering") seized power simultaneously in over 40 nations, with entire populations being bombed out of existence. Since this war did not begin in 1992, we are be forced to admit that the Star Trek timeline is apparently an alternate one to our own, having diverged some time after 1930. The theory of some third party print literature that the 40 simultaneous coups were all done in secret is not considered valid in this timeline. Spock made clear that the population became war weary and would have been afraid to know that over 80 of the "supermen" were still at large. This war was obviously NOT a secret in the Star Trek universe.

One additional note: Many spellings of planet names and people are difficult to pin down. The Star Trek Next Generation Companion was an invaluable source for proper spellings, as were various novelizations and other printed sources. Where no confirmed spelling is known, it has been necessary to...guess. 

Michael Marek