About this tool
Find the ISO week number for a selected date. This page explains the values requested and the method used so you can check whether the result fits your purpose.
How to use it
Enter Date.
Press Calculate, then review the result and the method below. Use Reset to clear the values in the calculator panel.
Method used
ISO weeks begin on Monday; week 1 is the week containing the first Thursday of the year.
Important assumptions and limits
Check that the units and values you enter are appropriate for your use case.
Date note: Check whether public holidays, time zones, contractual deadlines or local business rules matter for your situation. They are not automatically included unless stated on the tool.
Questions about this result
Are the values I enter sent to The Decimal Space?
No. This calculator processes the values in your browser. This page does not require a calculator account or a server-side save function.
Can I use this for an important decision?
Check the inputs, units, formula and any rounding. For a decision with legal, tax, financial, medical, engineering or safety consequences, use an official source or obtain advice from an appropriately qualified professional.
Why might a result differ from another calculator?
Different tools can use different inputs, rounding, units, assumptions or formulas. Compare the calculation method rather than relying only on a displayed number.