What is a day-of-year number?

A day-of-year number (also called an ordinal date) counts days from January 1 (day 1) through December 31 (day 365 or 366 in a leap year). It is a compact way to represent a date without month names.

How many days does a leap year have?

A leap year has 366 days. A year is a leap year if it is divisible by 4, except for century years which must be divisible by 400 (e.g., 2000 was a leap year but 1900 was not).

What day number is today?

The tool automatically pre-fills today's date so you can see today's day-of-year number and remaining days instantly when you open the page.

Is this the same as a Julian date?

A day-of-year ordinal date is sometimes loosely called a "Julian date" in business contexts, but the astronomical Julian Day Number (JDN) is a different, much larger number counting days since January 1, 4713 BC. This tool uses the simpler ordinal day-of-year system.

What is the maximum day number I can enter for reverse lookup?

For non-leap years the maximum is 365; for leap years it is 366. The tool validates your input and shows an error if you exceed the valid range.

Day of Year Calculator

Name: Day of Year Calculator
Availability: InStock
Author: Nham Vu

Enter a date to get its day-of-year number and days remaining, or enter a day number to find the matching calendar date.

Select a date

Enter a date or day number on the left to see results.

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Summary

Enter a date to get its day-of-year number and days remaining, or enter a day number to find the matching calendar date.

How it works

Enter any calendar date in the Date to Day Number tab.
The tool instantly shows the ordinal day number (1–365 or 1–366 for leap years).
It also calculates how many days remain in the year.
For reverse lookup, switch to the Day Number to Date tab.
Enter a year and day number (1–366) to find the matching calendar date.

Use cases

Find the ordinal date for scheduling, payroll, or compliance deadlines.
Calculate how many days are left in the fiscal or calendar year.
Convert Julian-style day numbers back to readable calendar dates.
Quickly check which calendar date a specific day number falls on.
Useful for programmers working with date libraries that use ordinal dates.
Verify leap-year day counts (February 29 = day 60 in a leap year).

Frequently Asked Questions

Last updated: 2026-06-24 · Reviewed by Nham Vu