What day number is today? What date is day 256? This day of the year calculator converts between calendar dates and day numbers (1-365, or 1-366 in leap years) in both directions.
Day of the year calculator
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Date to day number
Select any date in the top section. The calculator instantly shows which day of the year it is (1-365 or 1-366), the day of the week, and how many days remain in the year.
Day number to date
Enter a day number (1-366) and year in the bottom section. The calculator converts it to a calendar date and shows the day of the week. Leap years automatically allow day 366.
Notable day numbers
- Day 1: January 1 – New Year's Day
- Day 100: April 10 (April 9 in leap years)
- Day 183: July 2 – Midpoint of the year (July 1 in leap years)
- Day 256: September 13 – Programmer's Day (2⁸ = 256, though it's September 12th during Leap Years)
- Day 365/366: December 31 – Last day of the year
Leap years
The calculator handles leap years automatically. During leap years (2024, 2028, 2032...), February has 29 days, making 366 total. All dates from March 1 onward shift by one day number compared to non-leap years.
