The day of the year is the numbered position of a date within its year, counting 1 January as day 1. So 1 February is day 32, and 31 December is day 365 in a common year or 366 in a leap year. The day-of-year calculator gives this number for any date, along with the days remaining and how far through the year the date sits.
How to count it
To find the day of the year by hand, add up the lengths of the full months before the date, then add the day of the month. For 10 March in a common year, that is 31 days in January plus 28 in February plus 10, which is day 69. The day-of-year calculator does the addition for you and applies the correct February length for the year.
How a leap year shifts the count
Up to and including 28 February, the day numbers are identical in every year. After that, a leap year inserts 29 February, so every date from 1 March onward moves up by one. In a common year 1 March is day 60, but in a leap year it is day 61. This is why the calculator needs the full date rather than just the month and day: the year decides whether the extra day applies.
Other names for it
You may see this number called by a few names:
- Ordinal date, the formal term for a date given as a year and a day number.
- Day of year, often shortened to DOY in logs and data.
- Julian day, used loosely to mean the day number within the year, though strictly the Julian day is a different running count.
Where it is useful
The day-of-year number turns up in practical places:
- Logs and file names, where a compact day number sorts cleanly.
- Progress tracking, showing how far through the year a goal or review sits.
- Counting down, since the days left in the year follow straight from it.
Leave the date on today in the day-of-year calculator to see the current number and the days remaining. For why the count shifts mid-year, see how to tell if a year is a leap year.