Day of Year Calculator
Find the ordinal day number for any date, convert a day number back to a date, and see year progress, days remaining, ISO week and leap-year context.
Convert a date to its day number
English search intent for this tool is usually direct: enter a calendar date and get its ordinal day of year, from 1 on January 1 through 365 or 366 on December 31.
Leap years have 366 days, so dates after February 29 shift by one compared with common years.
What the calculator shows
- Day number in the selected year and total days in that year.
- Year progress, days elapsed and days remaining.
- ISO week, quarter and season for the selected date.
- Reverse lookup from day number to calendar date.
- February 29 handling without silently moving it to March 1 in common years.
Frequently Asked Questions
Sources and References
- DateMDN Web Docs
- Representing dates and timesMDN Web Docs
- Gregorian calendarBritannica
- ISO 8601 date and time formatISO
- International System of Units: TimeNIST
Calculations are based on the listed reference sources. Links open in a new tab.
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