Day of the Year Calculator

It is the ordinal position of a date counting from January 1 as day 1. In a common year December 31 is day 365, and in a leap year it is day 366. This number is sometimes called the ordinal date or the Julian day within the year.

The tool follows the Gregorian rule: a year is a leap year when it is divisible by 4, except centuries, which must also be divisible by 400. So 2024 and 2000 are leap years, while 1900 and 2100 are not, and February then holds 29 days instead of 28.

In a leap year such as 2024, February 29 is day 60. If you enter February 29 in a common year the tool shows an error, because that date does not exist and cannot have a day number.

It is the total days in the year minus the day number. On December 31 the result is 0 because no days follow it, and on January 1 it is 364 in a common year or 365 in a leap year.

The calculator validates the day against the real length of the month. Entering April 31 or February 30 shows a message like day must be an integer from 1 to 30, so you cannot get a misleading number from a date that never occurred.

Yes. It applies the same proleptic Gregorian rules to any whole year, including years before the calendar was adopted and years far in the future. Keep in mind that historical calendars in use at the time may have numbered days differently.

You can enter any integer year, including 0 and negative values, and the leap year math still applies. This matches the proleptic Gregorian calendar used by many programming libraries rather than the BCE and CE convention that skips year zero.

Yes. Every calculation runs in your browser with plain arithmetic, and nothing about the date you enter is uploaded or logged anywhere.

Yes. This tool has a JSON API that returns the day of year, days remaining, total days and the leap year flag for a year, month and day, so you can wire the same numbers into a script or spreadsheet.