Day of the Year Calculator

Find the day number of any date, from 1 to 365 or 366, and how many days are left in the year. The day of the year calculator also works backwards from a day number to a date.

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Day of the year
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How to use the Day of the Year Calculator

  1. Choose Day number of a date or Date of a day number.
  2. Enter the Date, or the Year and the Day number.
  3. Press Calculate. You get the day number or the date, with days left in the year and the ISO week.

How it works

day of the year = days since January 1 of that year + 1
days left = days in the year − day of the year
date of day N = January 1 + (N − 1) days

A leap year has 366 days, so dates from March 1 onward have a day number one higher than in other years.

Examples

  • September 26, 2026 is day 269, with 96 days left.
  • December 31, 2024 is day 366, because 2024 is a leap year.
  • Day 60 of 2024 is February 29, 2024.

Where day numbers are used

Day-of-year numbers appear in manufacturing batch codes, food packaging, astronomy, and some logistics systems, often written as YYDDD (the Julian date format). Programmers use them to compare dates quickly within a year.

Limitations

  • Years 1000 to 9999 are supported.
  • ISO weeks start on Monday; week 1 is the week with the year's first Thursday.

Frequently asked questions

What day of the year is it today?

Open the calculator; it starts with today's date and shows its day number.

How many days are in a year?

365, or 366 in a leap year.

What is a Julian date?

In industry it often means a year plus the day number, like 26269 for September 26, 2026. In astronomy it is a continuous day count.

Often used together with the Day of the Year Calculator.