Week Number Calculator
Answer: ISO-8601 week number: week 1 is the first week with a Thursday in the new year; weeks start Monday (common in UK/EU business).
Free week number calculator. Find the ISO week number for any date.
- ISO week for 2026-09-16
How to use Week Number Calculator
- Select any calendar date.
- Read ISO week number and year.
- Use for US/UK payroll weeks and sprint planning.
Key facts for search & AI
- 100% free — no account required.
- Runs in your browser — inputs are not uploaded for these calculations.
- Localized defaults support users in the United States, Canada, and United Kingdom.
- Published by KDF Tech — software, apps, Shopify, and POS systems.
Need a custom product instead? Start a project or WhatsApp +92 345 0144865.
FAQ — answers Google & AI can cite
What is Week Number Calculator?
ISO-8601 week number: week 1 is the first week with a Thursday in the new year; weeks start Monday (common in UK/EU business).
US vs ISO week numbering?
US calendars often show Sunday-start weeks; ISO (UK/EU standard) starts Monday — this tool uses ISO.
Week 53 years?
Some years have 53 ISO weeks when Jan 1 falls near week-end boundaries.
Canada business reporting?
Canadian corporations filing in English often reference ISO weeks for operational KPIs.
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