Ordinal Date Converter
Convert between ISO calendar dates and ordinal dates (year plus day-of-year 1-366) with leap-year aware math in your browser.
Convert between calendar dates and ordinal dates
An ordinal date (ordinal in the calendar sense) is a year plus the day-of-year from 1 through
366. Meteorologists, log analysts, and firmware teams often store timestamps as YYYY-DDD instead of
month and day. This converter works in UTC with leap-year rules so February 29 stays consistent.
How to use it
- Choose calendar to ordinal or ordinal to calendar.
- Enter either an ISO
YYYY-MM-DDdate or a year plus day-of-year. - Read the headline result and copy the detail block if you need both forms in one string.
Related tools: Date Format Converter, Day Percentage Elapsed.
Frequently Asked Questions
What timezone is used?
Calculations use UTC midnight boundaries so results match scientific ordinal date conventions.
What happens on leap day?
In leap years, day 60 is February 29. Non-leap years reject day-of-year values above 365.
Is this the same as ordinal numbers (1st, 2nd)?
No. For linguistic ordinals use the Ordinal Number Converter.
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