Day of the Year Calculator
Find the day number of a date, or the date for a day number.
What this tool does
The day of the year counts days from 1 January, which is day 1. 1 March is day 60 in a common year and day 61 in a leap year, and 31 December is day 365 or 366. Enter a date above to see its day number, or pick the other mode to turn a day number into a date.
Counts the days from 1 January to a date, inclusive of both ends.
Converts a day number back to a calendar date and adds the week, quarter and days remaining.
How to use it
- Choose whether to find a day number or a date.
- Pick a date, or enter a year and a day number.
- Read the day of the year, the days left and the ISO week.
- Copy or download the result.
Why use this calculator
Works in both directions: it gives the day number of any date, and turns a day number and a year back into a calendar date. Day numbers are used in logistics, manufacturing, farming, programming and data work, where dates are stored as a year and a day. Converting by hand means remembering which months are long and whether the year is a leap year.
Why we built it
We built the day of the year calculator to work in both directions, from a date to a day number and back, with the ISO week and the days left. See the week with the week number calculator and check leap years with the leap year calculator.
Who this tool is for
- Programmers and data analysts reading ordinal dates
- Warehouse and manufacturing staff decoding date codes
- Anyone curious how far through the year a date is
When to use it
- Reading a date code on a package or batch.
- Working with ordinal dates in data or software.
- Seeing how far through the year a date is.
- Planning against day numbers in a schedule.
How it works
The day number is the number of days between 1 January and the date, plus one. A year is a leap year if it divides by 4, except centuries that do not divide by 400, and leap years have 366 days. The ISO week follows ISO 8601, where weeks start on Monday and week 1 contains the first Thursday of the year.
Example: 1 March 2026 is 31 + 28 + 1 = day 60 of 365. In 2024, a leap year, 1 March is day 61, and 31 December is day 366. Day 100 of 2026 is 10 April 2026.
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| I want to | Find the day number of a date |
| Date | 2026-03-15 |
| Year | 2026 |
| Day number | 100 |
With those inputs, the calculator returns:
- Day of the year: Day 74 of 365
- Date: Sunday, 15 March 2026
- ISO date: 2026-03-15
- Days left in the year: 291
- ISO week number: Week 11 of 2026
- Quarter: Q1
- Share of the year gone: 20.3%
- Leap year: No
What you give it, and what you get back
| Item | Details |
|---|---|
| Date, or year and day number | A calendar date, or a year with a day from 1 to 365 or 366. |
| Output | Day number, date, days left, ISO week, quarter, share of the year and leap year. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Day 366 is rejected | The year is not a leap year. | Use a leap year such as 2028 or enter day 365. |
| My ISO week is different from the calendar week | ISO weeks start on Monday, and early January can belong to the last week of the previous year. | Use the ISO week shown; it can be 52 or 53 near the new year. |
| Astronomers call it a Julian day | The astronomical Julian day is a different count. | This tool gives the ordinal date, not the astronomical Julian date. |
Assumptions and limitations
- Gregorian calendar only.
- Dates before the year 1 are not supported.
Frequently asked questions
What day of the year is it today?
Pick today's date above to see the day number.
What is the day number of 31 December?
365 in a common year and 366 in a leap year.
How do I convert a day number to a date?
Choose "Find the date from a day number", enter the year and the day, and read the date.
Is the day of the year the same as a Julian date?
The ordinal date is often called a Julian day in industry, but the astronomical Julian day is a different count.
How many days are left in the year?
The result shows it under "Days left in the year".
Is my information sent anywhere?
No. The calculation runs in your browser and nothing leaves the page.