Week Number Calculator
Find the ISO week number, standard week, and full week range for any date
About Week Number Calculator
This tool shows two week numbering systems for any date you choose. The Standard Week (used in the US) runs Sunday through Saturday, with week 1 starting on January 1. The ISO Week (ISO 8601, used in Europe and most of the world) runs Monday through Sunday, with week 1 defined as the week containing the year's first Thursday.
The tool also shows the week-of-month number and the exact date range for both week types. All calculations happen in your browser — no data is sent to any server.
- 100% free — no account needed
- Runs in your browser
- Nothing is uploaded
Frequently asked questions
Is Week Number really free?
Yes. Week Number is completely free on PureBrowser — every feature, with no account, no trial, and no credit card.
Does Week Number upload my data?
No. Week Number runs entirely inside your browser, so anything you type, paste, or open stays on your own device.
Do I need to sign up or install anything?
Neither. There is no account and nothing to download — open the page and Week Number is ready to use on desktop or mobile.
Does Week Number work offline?
Once the page has loaded, yes. All of the processing happens locally in your browser, so it keeps working without a connection.
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