About the Day of the Year Calculator
Ordinal day number for a date, and the date for a given day number.
Also known as: julian day number, ordinal date calculator, what day number is it, days into the year.
How to use this calculator
- Enter calculate.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
day number = date − 1 January + 1
Worked example
Using the values pre-filled in the calculator above:
- Calculate: Day number from a date
- Date: 2026-09-22
the calculator returns:
- Day of the year: 265
- Days remaining: 100
- Year completed: 72.6%
- Days in this year: 365