Date calculators · Calendar lookups
Day of Year Calculator
Find the date behind day 100—or turn any date into a clear year-and-day label.
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Select your counting rules and calculate.
Calculation details
| Step | Value |
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How to use this calculator
Choose a calendar date to find its numbered position in the year. For reverse lookup, enter a year and day number. The result includes a padded YYYY-DDD label, remaining dates and each month's day-number range.
January 1 is day 1. Common years contain 365 days; leap years contain 366. Day 366 is rejected for a common year. Calendar-year progress measures completed date boundaries before the selected date, not a live clock percentage. Remaining days exclude the selected date.
A worked example
Day 60 of 2028 is February 29, written 2028-060. Day 60 of 2027 is March 1. The same day number can refer to different month/day dates in leap and common years.
Is an ordinal date the same as a Julian date?
No. YYYY-DDD is a year plus a day-of-year number that resets each January. An astronomical Julian Day Number is a continuous day count; the historical Julian calendar is another separate concept. This tool converts ordinal dates only.
Which calendar and years are supported?
These tools use Gregorian calendar dates for years 1–9999, without historical calendar-switch dates. They count dates, not elapsed hours. Today buttons use the current date in your browser's time zone.
What happens to my dates?
Calculations run on your device. Saving a calculation is optional and keeps it in this browser. A setup link contains the dates and settings you entered; anyone with the link can read them. Use one tab per saved calculator. Clear saved data from Privacy & settings.