Week Number Calculator
Get the ISO 8601 week number for any date — live, accurate, private.
See how it works
Watch a quick simulation of this tool in action — no file needed.
How to use Week Number Calculator
Follow these steps — everything happens instantly in your browser.
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Step 1. The top card shows the current ISO week number, updating live every second.
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Step 2. Pick any date with the date picker — the bottom card shows that date's week number.
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Step 3. Each card also shows the week-year (which may differ from the calendar year near Jan 1 or Dec 31).
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Step 4. Use “Today” to snap the picker back to the current date.
Why use this tool
Private by design
All processing happens locally in your browser. Open DevTools → Network and you'll see zero file uploads. Ever.
Instant
No upload wait, no queue, no server round-trip. Results appear the moment you drop a file.
Free & unlimited
No accounts, no watermarks, no daily caps. Use it as many times as you like, forever.
Works everywhere
Desktop, tablet or phone — every tool is responsive and installable as a PWA for offline use.
Frequently asked questions
Everything you might want to know about week number calculator.
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