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Week Number Calculator
Find the ISO week number of any date, the dates of any week, and a full list of weeks for a year.
Free, no uploads, no sign-up. Runs 100% in your browser.
How Week Number Calculator works
Worked out in your browser with your device clock and time zone. Calendar files follow the iCalendar standard (RFC 5545), so Google, Apple and Outlook all open them. ISO 8601 weeks start on Monday, and week 1 holds the first Thursday of the year.
Input: Date. Output: Text, CSV.
How to use Week Number Calculator
- Type a date or a week.
- Read the week and its dates.
- Download the year list.
Tips
- Times use your device time zone. Calendar files store times in UTC, so everyone sees their own local time.
- ICS files open in Google Calendar, Apple Calendar and Outlook.
Week Number Calculator FAQ
- Are my files uploaded?
- No. This tool runs entirely in your browser tab. Files are read from your disk into memory and the result is generated locally.
- Is it free? Are there limits or watermarks?
- Free and open source (MIT). There are no file-size caps, daily quotas, accounts or watermarks.
- Does it work offline?
- Yes, once the page (and any engine it needs) has loaded, it keeps working without a connection thanks to the service worker cache.
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- Merge Calendar Files: Combine ICS calendars into one, remove duplicates and keep only a date range or events with a word.