Stardates are based on Coordinated Universal Time, as this is an age where we have standardized our time around Greenwich Mean Time. Stardates are written as Year.Milliyear, keeping a standard tracking of time when handling astronomical travel.
How to Calculate Milliyear
Get the numbered day of the year.
Subtract one
Multiply that by 24 hours to get the number of hours since New Years.
Multiply by 60 to get the number of minutes since New Years.
(Optional) Convert current UTC to minutes and add them to the above result.
Divide that result by the Milliyear constants stated above.