Calculate your birthday

The mean tropical year is the average time between spring equinoxes. It is synchronized to the seasons and is currently about 365.242189 days, changing slowly. The commonly used gregorian calendar has on average 365.2425 days/year. Depending on what definition of "year" and which calendar you use, a specific date will likely drift through the seasons slowly. You may be born in summer, but 1000 calendar years later that date might be in winter. While this does not happen with the gregorian calendar in a typical human lifetime, it is still fun to celebrate your birthday in periods of one tropical year. This will vary your birthday date by one day sometimes.

Have fun!

Enter your birthday date+time.
Do stick to the input date/time format strictly or it will not work. Don't forget the seconds!

This program (source here) adds multiples of the mean tropical year (n*365.242189*86400) to your birthday with the addSeconds() function of the php pear Date package. It does not consider time zones so if you enter local time it should print local time correctly - I hope. You probably get 1h wrong results if your birthday jumps between daylight savings time and standard time. Leap seconds are enabled, but they are, of course, unknown for the future. Leap seconds will only be added at the correct moment if you use UTC but they don't matter in most cases, anyways.

Privacy: Your date and time of birth will be transmitted with the POST method and so will not be stored in the web server log files unless you use URLs such as .

Please send any bugs, comments, etc. to me (email address protected by intelligence test).

Bernhard Kuemel