Day of the Year Calculator
See which day of the year a date is, how many days are left in the year and what share of it has passed. The other way round, find the date of a day number such as the 200th day of the year.
- Days in the year365
- Days left in the year59 days
- Share of the year done83.8%
- ISO ordinal date2026-306
- ISO weekWeek 45 (2026)
How it is calculated
Day numbers (sometimes called “Julian dates”, though not the astronomers’ Julian day count) are common in production batch codes, expiry codes, lab and logistics records. In a leap year 29 February is day 60, so every date after 1 March has a number one higher than in a common year. The share of the year done is the day number divided by the year’s length.
Day number = Date − 1 January + 1; Days left = Length of the year − Day numberA year has 365 days, 366 in a leap year: years divisible by 4, except century years not divisible by 400. The ISO ordinal date writes the year and a three-digit day number (2026-296).Example
15 March 2025: 31 (January) + 28 (February) + 15 = day 74; 2025 is not a leap year, so 291 days are left and 20.3% of the year is done.
Frequently asked questions
What day of the year is today?
The date field opens on today, so the result is today’s day number, with the days left in the year beside it.
When is the 256th day of the year?
Choose “date of a day number” and enter 256. It is 13 September in a common year and 12 September in a leap year (Programmers’ Day).