Ordinal Day of Year

Satellite files, weather series and planting spreadsheets often label a day by its number within the year: 185 instead of July 4. When one of those numbers lands on your desk, or you have to produce one, counting month by month is tedious and easy to get wrong. Sometimes the question is even simpler: how many days are left before the year closes.

Counting starts at 1 for January 1 and ends at 365, or 366 in a leap year. February 29 pushes everything after it: July 4 is day 185 in 2026 and day 186 in 2024. The field only accepts YYYY-MM-DD with leading zeros, so 2026-5-3 is rejected; write 2026-05-03. The output also tells you whether the year is a leap year.

Double-check what you typed, because the page does not validate month lengths: 2026-02-30 is accepted and returns 61, which is really March 2. If your computer sits in a time zone with daylight saving, sanity-check the count after the spring change. This number is neither the ISO week nor the astronomical Julian day. It is all computed in your browser.