When Is My Birthday?

When were you born? (Date and time)

That's not a valid date. Try using the format "MM/DD/YYYY HH:MM am/pm"

Try using the format "MM/DD/YYYY HH:MM am/pm"

We're pretty sure you're not that old. Please enter a date after 1900.

Get your solar birthday and time for what year?

Enter the year in which to check your birthday.

Please enter a date after 1900.

Your solar birthday is:

What on earth am I looking at?

This site provides a method for calculating your solar birthday: the date and time at which the earth passes through the same place in its orbit that it was when you were born.

What is a solar year?

A calendar year is either 365 or 366 days long, whereas a solar (or tropical) year is 365.2421897 days long. A calendar year represents all the days in the Gregorian calendar. A solar year represents the average time between equinoxes, or how long it takes the earth to run through all four seasons. This difference in length creates the need to add leap days to the calendar and causes people to celebrate their birthdays up to 16 hours early or late.

So what's the problem?

Disregarding leap years for a second, the time between when you were born and your first birthday was 365 days, or about 5 hours and 48 minutes short of a full solar year. By your second birthday the error was over 10 hours and by the third, it was about 16 hours, enough to actually push your birthday to a different calendar day. By the fourth year, the error would be greater than a full day, except that a leap day was added sometime before your fourth birthday and cleared out most of the error.

How does this work?

The algorithm used by the calculator above takes into account the length of a solar year, the amount of error built up over time, and the number of corrective leap days between birth and the specified birthday year. The result is the adjusted date and time at which optimal partying may take place. The site uses knockout.js and date.js for data-binding and datetime manipulation and everything stays client-side. So, no, this is not a front for a DOB harvesting scheme.