Calculate your leap birthdays

A birthday is meant to be celebrated the moment that you are one year (365 days) old. But a year is actually a bit longer than 365 days; an astronomical year (the earth completing one trip around the sun) is about 365.25 days long. That’s the reason we have invented leap years.

Birthday cake
Happy Birthday
This also means that you should celebrate your first birthday at 365.25 days after you are born. And your second birthday at 730.5 days. Depending on what time you were born, this could be on another date than the date on which you were born. Click here for more information.

Let’s calculate when you should celebrate your birthdays. Use the form below.

Calculate your birthday celebrations

In the form enter your birth date and indicate what time you were born.

You don’t need to know the exact time of birth; just indicate in which quarter of the day you were born.


Time of birth:

Note! The calculation uses a year of 365.25 days (365 days plus 6 hours). But a complete trip around the sun takes 365.2425 days. That is 365 days, 5 hours, 49 minutes and 12 seconds. So that’s about 11 minutes less than the 365 days and 6 hours.

Of course I could have written a script that calculates with a year of 365,2425 days. That would be more accurate, but it would require that you know the exact moment of your birth. Being born a few minutes earlier or later can, a few decades later, result in a different birthday celebration. As most people don’t know their exact birth moment, this slighly less accurate method has been used.

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