Get the ISO 8601 and US week numbers for any date. The ISO standard is universal in Europe and increasingly in tech, while the US variant is common in North America.
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How it works
ISO 8601: week 1 is the week containing the year's first Thursday. Weeks start on Monday. US: weeks start Sunday, week 1 contains January 1.
Key features
- Both ISO and US week numbers
- Handles year boundaries correctly
Common use cases
Sprint planning
Many agile teams number sprints by ISO week.
Manufacturing
European factories run production by ISO week.
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Pro tips
- ◆Use ISO for anything international. Only use US week numbers if your audience is exclusively American.
Common mistakes to avoid
- ✕Assuming week 1 always contains January 1 — in ISO it doesn't.
Frequently asked questions
How many weeks are in a year?▼
52 in most years, 53 in years starting on Thursday (or leap years starting on Wednesday).
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