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ISO Week Date Converter

Convert a calendar date into an ISO week date, or convert a week date back to a calendar day.

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1. Set up your workspace

ISO weeks begin Monday and week 1 contains the first Thursday. The week-numbering year can differ from the calendar year near New Year. Dates are calendar-only with no timezone conversion.

2. Review & use your result

Review the example inputs, then use convert date.

Report / export preview

Generated file contents

Using ISO Week Date Converter

Convert a calendar date into an ISO week date, or convert a week date back to a calendar day.

Enter conversion and calendar date. Try the example to see the format.
Convert date and review the result, including the assumptions shown below the inputs.
Copy, download or print your result. Editing an input clears the previous result.

Example

The included example: Calendar date — 2026-10-07; ISO week date — 2026-W41-3.
Change the inputs and generate a new result to compare it.

Questions & answers

How do I use this tool?

Convert a calendar date into an ISO week date, or convert a week date back to a calendar day. Load the editable example, replace its values and use the main action button.

What should I check before using the result?

ISO weeks begin Monday and week 1 contains the first Thursday. The week-numbering year can differ from the calendar year near New Year. Dates are calendar-only with no timezone conversion.

Are my entries saved?

Processing runs in your browser without a tool account or saved history. Download your result to keep a copy. Website advertising follows our privacy information.

Can I export or print it?

Copy and file download are available after generating a result. Print produces a clean copy of the visible result; use your browser’s Save as PDF option if needed.

Why can January belong to the previous ISO year?

ISO week 1 is the week containing the first Thursday. Early January dates can still be in week 52 or 53 of the previous week-numbering year. The result shows both week-year and calendar date.