How does Week Number handle timezones?

Week Number uses the browser's Intl API and your device's system timezone by default — no server round-trip. Where the tool involves multiple zones, you can pick each zone explicitly from an IANA-standard list (America/New_York, Asia/Tokyo, etc.).

Does Week Number account for daylight-saving time?

Yes. Week Number uses the IANA timezone database via the browser, which includes historical and future DST rules for every zone. Cross-DST calculations are correct even when spanning the spring-forward or fall-back date.

What date formats does Week Number accept?

Week Number accepts ISO 8601 (2026-07-23), US (07/23/2026), European (23/07/2026), and Unix timestamps (seconds or milliseconds). Ambiguous input is flagged inline so you can pick the correct interpretation.

Is my date input private?

Yes. Everything runs in your browser — dates entered into Week Number are never uploaded, logged, or shared. Refresh the page and it's gone.

Can Week Number handle historical dates before 1970?

Yes for calendar-based tools (age, date difference, days between). Unix timestamp tools work with negative values for pre-1970 dates, but some third-party systems reject negative epochs — check the target system's docs.

Is Week Number free and unlimited?

Yes — no signup, no limits, works on every device. Completely free.

Week Number

Find ISO week number of any date.

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Week Number

Find ISO week number of any date.

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Week Number

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