Day of Year Calculator
Find which day of the year any date is, how many days are left and which ISO week it falls in, or turn a day number back into a date.
The day of the year counts from 1 on January 1 to 365 on December 31, or 366 in a leap year. October 6, 2026 is day 279, which leaves 86 days in the year and means 76.4% of 2026 is done by the end of that day. It falls in ISO week 41. Enter any date to get its day number, or a day number to get the date.
This calculator uses the Gregorian calendar for years 1 to 9999 and ISO 8601 week numbers only; it does not show US-style Sunday-start week numbers or fiscal weeks, and the share of the year counts whole days to the end of the date, not the time of day. The today button uses your device's date and time zone.
Date to day number
Tuesday, October 6, 2026
Day 279 of 365
- Days left in the year
- 86
- Share of the year done (end of day)
- 76.4%
- ISO week
- Week 41
- Leap year
- No (365 days)
Day number to date
Day 100 of 2026
Friday, April 10, 2026
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About the Day of Year Calculator
Counting days from the start of the year is handy for project schedules, habit streaks, school and fiscal calendars, and reading the three-digit day codes stamped on some products. The calculator adds the days in each full month before your date to the day of the month, and adds one more after February in a leap year, which is any year divisible by 4 except century years not divisible by 400: 2024 was a leap year, so December 31, 2024 was day 366, while 1900 was not. Going the other way, it walks through the months until the day number runs out, so day 100 of 2026 is Friday, April 10, 2026. The week number follows ISO 8601, the standard most of Europe and many business systems use: weeks start on Monday and week 1 is the one that contains the year's first Thursday. That rule makes some years 53 weeks long, 2026 among them with 53, and it can put the first days of January in the previous year's last week: January 1, 2021 fell in week 53 of 2020. US calendars that start weeks on Sunday can number weeks differently, so check which system your schedule uses.
Frequently asked questions
What day of the year is it today?+
Press the button to fill in today's date from your device and the calculator shows its day number, the days left and the week number. The answer changes at midnight where you are.
How many days are in a year?+
365 in a common year and 366 in a leap year, when February has 29 days. Leap years are the years divisible by 4, except century years, which must also be divisible by 400, so 2000 was a leap year and 2100 will not be.
Why does my calendar show a different week number?+
This calculator uses ISO 8601 weeks, which start on Monday with week 1 containing the first Thursday of the year. Many US calendars start weeks on Sunday and call the week containing January 1 week 1, so the two can differ by one, especially in early January and late December.
Is the day of the year the same as a Julian date?+
In everyday use, often yes: a Julian date on packaging or in military paperwork is usually the year followed by the day number, such as 26279 for day 279 of 2026. Astronomers use Julian date for something else, a running day count; the Julian date calculator on this site converts both.
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