Calendar

ISO Week Number Calculator

Find the ISO week number and week-year, including dates around New Year.

Your dates

On this device

Your dates are remembered here for 30 days. No account needed.

Your story in numbers

Every date has a story.

Enter your dates to discover your result and the next dates worth keeping.

YOUR NEXT DISCOVERY

One date. More ways to see it.

Compatible dates follow you to the next tool.

Calendar

Day of Year Calculator

Convert a date to its day-of-year number, or find the date for an ordinal day.

Open tool →

Calendar

Year Progress and Days Remaining

See days elapsed, days remaining and progress through the year.

Open tool →

Understanding your result

These results use the Gregorian calendar. They describe the date entered without assuming local working, legal or historical-calendar rules.

See a worked example

Illustrative example, as of September 13, 2026.

Date to explore: 2026-09-13

37 ISO week

Are my dates sent to a server?

Calculations run in your browser. Your dates stay on this device unless you choose to include them in a sharing link or image. “Clear my dates” removes them from local storage.