Why Use This Tool?
Manufacturing dates, academic calendars, firmware build stamps, weather records — plenty of systems count days as a simple number from January 1st instead of writing out dates. This calculator converts in both directions: any date to its ordinal day number, and any day number back to its date.
Leap years are handled automatically — day 60 is February 29 in 2024 but March 1 in 2023 — and every result shows the year's total days plus how many remain.
How It Works
- Pick a date to get its day-of-year number and days remaining.
- Or enter a year and a day number to find the calendar date.
- Check the back-conversion line — the tool verifies its own answer.
Frequently Asked Questions
What day of the year is it today?
The date field opens on today — click 'Get day number' and you'll see the ordinal day, the year's total days, and how many remain.
What is the day number of the year used for?
Ordinal dates (YYYY-DDD) appear in manufacturing codes, military and scientific logging, and build numbers — a compact, unambiguous date format.
How do I convert a day of year back to a date?
Enter the year and the day number in the second converter — leap years are handled, so day 60 lands on Feb 29 or Mar 1 depending on the year.
Tips & Things to Watch
- Ordinal format is YYYY-DDD: 2026-041 means February 10, 2026.
- Day 256 is a programmer holiday (2^8) — September 13 in common years.
- Watch leap years: after February, every ordinal date shifts by one day.