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Week Number Finder
ISO week number for any date
Week Number
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Week No.
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Year
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Quarter
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What is a Week Number Calculator?
Finds the ISO week number of any date - useful for project management, financial reporting, and employee scheduling.
How It Works
ISO 8601 week numbering: weeks start Monday. Week 1 is the week containing the first Thursday of the year.
Example
Jan 1, 2024 = Week 1. Dec 31, 2024 = Week 1 of 2025 (ISO). Total 2024: 52 full weeks + 2 extra days.
Pro Tips
- ISO weeks always start on Monday - important for international scheduling and reporting.
- Week 53 occurs when Jan 1 or Dec 31 is a Thursday (roughly every 5-6 years).
- Project management tools (Jira, Asana) use ISO week numbers for sprint and milestone planning.
- Indian financial quarters: Q1=Apr-Jun, Q2=Jul-Sep, Q3=Oct-Dec, Q4=Jan-Mar.
FAQ
What is ISO week numbering?▼
ISO 8601 standard: weeks start Monday; Week 1 contains the year's first Thursday.
How many weeks in a year?▼
52 full weeks always; 2 or 3 extra days mean some years have an ISO week 53.
Why can week 1 start in December?▼
If Dec 29-31 fall in a week whose Thursday is in January, those days belong to next year's Week 1.
Do all countries use the same system?▼
ISO 8601 is international; the US sometimes starts weeks on Sunday with Week 1 = Jan 1.