Date & Time Tools
Calendar Week Number Calculator
Find the ISO week number of any date.
Loading tool…
What is Week Number?
The ISO week-numbering year differs from the calendar year around January and December. This tool computes the correct ISO week for any date.
How it works
ISO weeks start on Monday; week 1 is the week containing the first Thursday. The calculation follows that definition exactly.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Paste or type any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.