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Find the ISO week number for any date, see what day of the week it falls on, and discover the date range for any week. Useful for project planning, payroll, and business reporting.
ISO 8601 defines a standard week numbering system used widely in Europe, project management, and business reporting. Weeks always start on Monday and Week 1 is defined as the week containing the year's first Thursday.
This means January 1 might fall in Week 52 or 53 of the previous year, and December 31 might fall in Week 1 of the next year.
Enter your values into the input fields above and click Calculate for instant results. All calculations run in your browser — no data is sent to any server, ensuring complete privacy. Use the Copy button to save your results and the Share button to send a link to this calculator.
Results are based on the formula and inputs provided. For important financial, medical, or legal decisions, always verify results with a qualified professional. This tool is designed to give quick, reliable estimates for planning and educational purposes.
Always double-check your input values and units before calculating. Small input errors can significantly affect results. Use the Reset button to clear all fields and start fresh. For multi-step calculations, use the result of one calculation as the input for the next.
| Term | Meaning | Example |
|---|---|---|
| Input | Value you enter into the calculator | Amount, rate, or quantity |
| Output | Calculated result shown after clicking Calculate | Final answer or converted value |
| Formula | Mathematical equation used for the calculation | Shown in Formula section above |
| Precision | Number of decimal places in the result | Typically 2-4 decimal places |
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