Day-of-Year Calculator

Worked example

December 31, 2028 is day 366 of that year, since 2028 is a leap year with 366 total days. In a non-leap year, December 31 is always day 365. March 1, 2028 is day 61 in that leap year, one day later than the day 60 it would be in a common year, because February 29 pushes every subsequent ordinal day forward by one for the rest of the year.

Common mistakes

• Assuming a given date has the same ordinal day number every year. Any date from March onward shifts by one in a leap year, since February contributes an extra day before it.
• Forgetting to check whether the target year is a leap year before comparing two years' ordinal days directly. A day-of-year count is only comparable across years once the leap-year offset is accounted for.

Limitations

This is calendar arithmetic only. It does not reflect a fiscal or academic year, which often starts on a different date than January 1, so a "day 45 of the year" answer here will not match a fiscal-year day count unless the fiscal year also starts January 1.