The ordinal day of the year — 1 for January 1, 365 or 366 for December 31. Useful for scientific measurements, agricultural planning and Julian date calculations.
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How it works
Days elapsed since December 31 of the previous year. Leap years are auto-detected so February 29 gets its own ordinal.
Key features
- Ordinal day 1–366
- Progress bar showing year completion
- Remaining days in the year
Common use cases
Astronomy
Day-of-year is commonly used for orbital calculations.
Agriculture
Frost-date planning uses day-of-year.
Fitness tracking
"Day 205 of my streak"
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Pro tips
- ◆Day 100 falls on April 10 in common years, April 9 in leap years.
Common mistakes to avoid
- ✕Confusing Julian day (a separate astronomical concept) with day-of-year.
Frequently asked questions
What's day 366?▼
Only exists in leap years — always December 31.
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