I recently began playing the massively multiplayer online role-playing game (MMORPG) Star Trek Online (STO), which is now free to play. Since I am interested in stardates, I checked out how they were used in the game. You can access them through your logs by hitting "J". Your milestones in the game are all stamped with the real-life calendar date and a stardate. This allowed me to determine the basis for their stardate calculations. There is an STO stardate calculator already, but it's a little off, and does not make the basis clear.
The game is set in the year 2409, about 45 years after the beginning of Star Trek: The Next Generation (TNG), and about 30 years after the last TNG movie, Star Trek: Nemesis. The game was released in February 2, 2010 (55229), but the in-game year has remained 2409 two years later, and presumably was also 2409 during the beta testing in 2009, so it may be that the year was intended to be exactly 400 years in the future.
The current stardate in STO is about 90132. From archived discussions online, I have determined that the stardates were around 87700 when it was released. Coincidentally, according to the stardate calculator at TrekGuide.com, these are the stardates exactly 400 years in the future. At least, according to my recollection of TrekGuide's formula, which counted exactly 1000 stardates per year, starting from May 25, 2322 (169296).
However, when I went to check on TrekGuide.com, the dates did not work out. Instead of 90131 for this date in 2412, I get 86330. What's going on, I wondered? On examining TrekGuide's web page, I found that there are actually 918.23186 stardates per year, counting from July 5, 2318. Could I have misremembered so badly? Thanks to the Wayback Machine, I was able to determine that my recollection was, in fact, correct. Sometime between July 2010 (55399.860509) and July 2011 (55759.40857) the page was changed. (Update: It looks like it actually happened around April 7, 2011 (55658).) IMHO, I believe that they're over-thinking it, and should have stuck with the original formula. I doubt that Star Trek's creators were that accurate.
STO is, in fact, using the original TrekGuide stardate formula, as it was when the game was released, but shifted 400 years. That means that I can calculate STO stardates for the present era as exactly 1000 per year, beginning from May 25, 1922. This gives an alternative to the "contemporary" stardates that TrekGuide gives, which are based on air dates from 1987-2001. Using TrekGuide's (original) TNG stardate calculator with dates exactly 400 years from now gives stardates at most a few hours off, so it just needs a little tweaking.