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Week Number

Find week number of any date online

What is the Week Number?

The week number works like this: it returns the ISO-8601 week number, the week's Monday-Sunday range and the quarter for any date. Everything happens on your device - the input never leaves your tab unless the tool clearly states it performs a server-side lookup.

How to use the Week Number

1. Enter the date, time or duration you start from.
2. Add the operation's parameters.
3. Read the result, which updates live.
4. Copy values you need elsewhere.

Features

• Find week number of any date online
• Instant result, no page reload
• Works in any modern browser, desktop or mobile
• Free with no signup

Common mistakes to avoid

• Swapping day and month when entering dates

Examples

Input	Result
20 Sep 2026	ISO week 38 · Mon 14 Sep - Sun 20 Sep · Q3

Best used for

• Getting a reliable answer for week number without installing an app
• One-off tasks done in under a minute from any device
• Checking results before committing them to something important
• Working on a phone where desktop software is unavailable

Privacy

Date math runs locally in your browser.

Frequently asked questions

Why is 1 Jan sometimes week 52?

ISO weeks belong to the year containing their Thursday - a 29 Dec Monday can be week 1 of the NEXT year, and 1-3 Jan can belong to week 52/53 of the previous one.

What makes a week number ISO-8601?

Weeks start on Monday, and week 1 is the week containing the year's first Thursday - so Jan 1 can belong to the previous year's week 52/53, which the tool reports correctly.

What extra context comes with the number?

The week's Monday-Sunday date range and the quarter the date falls in - the two facts that make "week 37" meaningful without a calendar in hand.

More like this

Zoven offers 200+ free browser tools. Browse by category - Calculators, Converters, Generators, Developer Tools and Media Tools - or read workflow guides on the Zoven blog.