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Day of the Year Calculator
See which day of the year any date is, from 1 (January 1) to 365 or 366, along with the days left in the year, the ISO week number, the quarter and the ordinal date. Or enter a day number and a year to get the calendar date.
What do you want to find?
Gregorian year (1583–9999).
1 = January 1. Up to 365, or 366 in a leap year.
Enter your values to see the result.
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How to use the Day of the Year Calculator
- Choose a mode: day number of a date, or date from a day number.
- Pick a date (today is filled in), or enter a year and a day number.
- Press Calculate; results update as you type.
- Read the day number, days left, ISO week, quarter and leap-year status.
- Use the month table to look up the first and last day number of every month.
Day of the year formula
day of year = (days in all earlier months) + day of the month. Add 1 for dates after February 28 in a leap year. The days left in the year are 365 (or 366) − day of year.
First day number of each month
| Month | Common year | Leap year | Month | Common year | Leap year |
|---|---|---|---|---|---|
| Jan 1 | 1 | 1 | Jul 1 | 182 | 183 |
| Feb 1 | 32 | 32 | Aug 1 | 213 | 214 |
| Mar 1 | 60 | 61 | Sep 1 | 244 | 245 |
| Apr 1 | 91 | 92 | Oct 1 | 274 | 275 |
| May 1 | 121 | 122 | Nov 1 | 305 | 306 |
| Jun 1 | 152 | 153 | Dec 1 | 335 | 336 |
Example: August 20 in a common year is 213 + 19 = day 232. Some well-known day numbers: day 100 is April 10 (April 9 in a leap year), day 183 is the middle of a common year (July 2), and day 256 is September 13 (September 12 in a leap year), celebrated as Programmers' Day.
Frequently asked questions
How do I calculate the day of the year?
Add up the days in all the months before the date, then add the day of the month. March 15 in a common year is 31 (January) + 28 (February) + 15 = day 74. In a leap year February has 29 days, so it is day 75.
How many days are in a year?
A common year has 365 days and a leap year has 366. Leap years are divisible by 4, except century years, which must be divisible by 400. So 2024 and 2028 are leap years, 2100 is not, and 2000 was.
What day number is December 31?
December 31 is day 365 in a common year and day 366 in a leap year.
What is an ordinal date?
An ordinal date writes a date as the year plus the day number, for example 2026-074 for March 15, 2026. It is defined in ISO 8601 and is often used in manufacturing lot codes, logistics and science, where it is sometimes loosely called a Julian date.
Is the day of the year the same as the Julian Day?
No. The day of the year restarts at 1 every January 1. The astronomical Julian Day Number is a continuous count of days since 4713 BC (for example, January 1, 2026 is JD 2,461,042). Use a Julian date converter for that.
How is the ISO week number defined?
ISO 8601 weeks start on Monday, and week 1 is the week that contains the year's first Thursday. Because of this, the first days of January can belong to the last week of the previous year, and late December can be week 1 of the next year.
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