Week Number Calculator
// Find the ISO week number for any date
#About Week Number Calculator
Free online ISO week number calculator. Find the week number for any date according to the ISO 8601 standard. This tool runs entirely in your browser — your data is never sent to a server. Just paste your input, get instant results, and copy with one click. No sign-up or installation required.
#FAQ
How is the ISO week number determined? ▾
ISO 8601 defines week 1 as the week containing the first Thursday of the year. Weeks start on Monday.
Can the ISO week year differ from the calendar year? ▾
Yes, dates in early January may belong to the last ISO week of the previous year, and late December dates may belong to week 1 of the next year.
</> Embed this tool ▾
Copy this code to embed the tool on your website. Adjust the height to fit your layout.
<iframe src="https://www.browserutils.dev/embed/week-number-calculator" width="100%" height="500" frameborder="0" title="Week Number Calculator"></iframe>