A stardate is a system of time measurement developed by the Federation. In Starfleet, the use of this date system is commonly heard at the beginning of a voice log entry, such as "Captain's log, stardate 41153.7. Our destination is planet Deneb IV …". While the original method was inspired by the Julian date system currently used by astronomers, many ways have been used to calculate this date using different methods over the years, some more arbitrary than others. This makes it challenging to convert many stardates into equivalent calendar dates.
The calculations area, explains how we convert to the UFPGC's stardate. The base stardate uses a variety of dates throughout the years, while Federation Day is another date that can be used. Currently, the UFPGC uses Thurday, September 8th, 1966, as its base date (Star Trek Day).
An average Earth year comprises 365.2422 mean solar days
918.23186 Stardates = 1 year
0.00108904956 year = 1.0 Stardate
0.397766856 day = 1.0 Stardate
34,367.0564 seconds = 1.0 Stardate
34367056.4 milliseconds = 1.0 Stardate
The Voyager episode "Homestead" stated Stardate 54868.6 was on April 6, 2378 (TrekGuide)Star Trek Day - Thursday, September 8th, 1966, 20:30 (Premiered on NBC)
UFPGC - Friday, May 8th, 1987, around midnight
WikiHow - Friday, May, 23rd, 2008, around midnight
TrekGuide - Friday, July 5th, 2318, around noon
Star Trek: Discovery - Tuesday, March 18th, 2859, around midnight
NOTE: Discovery traveled to the year 3188, giving a stardate of 865211.3, using the current system on calculations.