Day of the Year
Today's ordinal day number (1 to 365 or 366) — how far through the calendar year we are. Also shows days remaining and year progress.
Any date → day of the year
Pick any date to find its day-of-year number.
What "day of the year" means
The day of the year (also called the ordinal date or Julian Day Number in calendar context) is simply how far through the year we are — a number from 1 (January 1) to 365 or 366 (December 31).
It's a convenient way to:
- Measure year progress — "we're on day 113, so we're about 31% through the year."
- Skip month/day arithmetic — comparing two dates becomes simple subtraction.
- Track deadlines — "project complete by day 250" is cleaner than "by the 7th of September."
- Format timestamps — the mainframe YYDDD format uses this number directly.
Days of the year by month
In a common (non-leap) year, the first day of each month falls on these day numbers:
| Month | Day of year of the 1st | Day of year of the last day |
|---|---|---|
| January | 1 | 31 |
| February | 32 | 59 (60 in leap) |
| March | 60 (61 in leap) | 90 (91) |
| April | 91 (92) | 120 (121) |
| May | 121 (122) | 151 (152) |
| June | 152 (153) | 181 (182) |
| July | 182 (183) | 212 (213) |
| August | 213 (214) | 243 (244) |
| September | 244 (245) | 273 (274) |
| October | 274 (275) | 304 (305) |
| November | 305 (306) | 334 (335) |
| December | 335 (336) | 365 (366) |
What about leap years?
In a leap year (366 days), February 29 is day 60. Every date from 1 March onward has a day-of-year number one higher than the same date in a common year. December 31 becomes day 366 instead of 365.
A year is a leap year if it is divisible by 4, except century years must also be divisible by 400. So 2000 was a leap year but 1900 wasn't. 2024, 2028, 2032, and 2036 are leap years; 2026 is not.
Practical uses for the day-of-year number
Day-of-year (sometimes called the ordinal date) is the simplest possible way to identify a date within a given year. It's used in:
- Spreadsheets — subtracting dates in Excel returns a day count; DOY helps visualize "where in the year" a deadline falls.
- Scientific research — climate data, astronomical measurements, and agricultural records are often indexed by DOY.
- Astronomy — star positions and almanac data use DOY alongside or instead of calendar dates.
- Finance — some interest-rate calculations work in day counts rather than months.
- Software — compact log file names (
2026-113.log) and backup rotations.
DOY reference table — what day number is it?
In a common year, here are the day numbers for the first and last day of each month. Add 1 to each March-through-December entry in a leap year.
| Month | Starts on | Ends on | Length |
|---|---|---|---|
| January | 1 | 31 | 31 |
| February | 32 | 59 (60) | 28 (29) |
| March | 60 (61) | 90 (91) | 31 |
| April | 91 (92) | 120 (121) | 30 |
| May | 121 (122) | 151 (152) | 31 |
| June | 152 (153) | 181 (182) | 30 |
| July | 182 (183) | 212 (213) | 31 |
| August | 213 (214) | 243 (244) | 31 |
| September | 244 (245) | 273 (274) | 30 |
| October | 274 (275) | 304 (305) | 31 |
| November | 305 (306) | 334 (335) | 30 |
| December | 335 (336) | 365 (366) | 31 |
Values in parentheses apply to leap years. For quick mental math: multiply months by 30 and add the day, then subtract a small correction. Day 100 ≈ April 10; day 200 ≈ July 19; day 300 ≈ October 27.
How to calculate DOY manually
If you need to work out the day of the year by hand:
- Start with the day-of-month (e.g., 15 for April 15).
- Add cumulative days up to the previous month. For April, that's Jan (31) + Feb (28 or 29) + Mar (31) = 90 (91 in leap year).
- Total: April 15 is day 105 (106 in leap year).
Or just use the calculator above.