How to use
Choose Date to day number and enter a real date to get its ordinal day and days remaining.
Choose Day number to date, enter a year and an integer from 1 to 365 or 366, then calculate.
Formula
The ordinal is 1 plus the number of elapsed days since January 1. January 1 is day 1; December 31 is day 365 in a common year and day 366 in a leap year.
Examples and limits
2024-02-29 is day 60, and day 366 of 2024 is 2024-12-31. Day 366 is invalid in 2023.
This tool uses years 0001–9999 in the proleptic Gregorian calendar. It does not convert Unix time, time zones, or ISO week numbers.
Frequently asked questions
Is January 1 day 0 or day 1?
Day 1.
Does February 29 change later day numbers?
Yes. Dates after February are one ordinal higher in a leap year.
Is this an ISO week calculator?
No. Ordinal days and ISO week numbers are different systems.