Time Tools
Week Number Calculator
Calculate week number for any date. Find out what week of the year it is and plan by week numbers.
Use Week Number Calculator to get instant results without uploads or sign-ups. Everything runs securely in your browser for fast, reliable output.
Your results will appear here.
About this tool
Week numbers provide a standard way to refer to weeks within a year. Our Week Number Calculator uses the ISO 8601 standard, where weeks run Monday-Sunday and Week 1 contains the first Thursday of the year.
Businesses, project managers, and many countries use week numbers for scheduling, planning, and communication. Simplifies tracking and avoids confusion with varying month lengths.
Usage examples
Current Week
What week number is it today?
December 15, 2024 = Week 50 of 2024
Project Planning
Schedule by week numbers
Project runs Week 10-15 (early March to mid-April)
How to use
- Enter a date (MM/DD/YYYY) or use today's date.
- Click "Calculate" to find week number.
- View week number, year, and date range.
- Use ISO 8601 standard week numbering.
Benefits
- ISO 8601 standard
- Week number for any date
- Project planning
- International standard
- Simplified scheduling
- Year-round tracking
FAQs
How many weeks are in a year?
Most years have 52 weeks. Some years have 53 weeks (long years) when January 1 falls on Thursday or leap years where January 1 falls on Wednesday. 52 weeks = 364 days, so there's usually 1-2 extra days.
What is ISO 8601 week numbering?
ISO 8601 is the international standard: weeks run Monday-Sunday, Week 1 is the first week with Thursday in it (contains January 4), and week belongs to year containing most of its days. Standardizes global communication.
Why do some countries use week numbers?
European countries commonly use week numbers for business, manufacturing, and logistics. Benefits: standardized scheduling, simplifies multi-month planning, avoids "what month" confusion, better for shift work, and international coordination. "Deliver in Week 23" is clearer than "late May/early June".
How do I calculate week number manually?
Manual calculation: (1) Find days since January 1, (2) Add day of week of January 1, (3) Divide by 7 and round up. ISO method is complex - easier to use calculator. Week 1 starts with first Thursday of year.
What is fiscal week numbering?
Fiscal weeks align with business calendars, not calendar years. Retail uses 4-5-4 calendar (4 weeks, 5 weeks, 4 weeks per quarter). Fiscal week 1 starts with fiscal year start (often not January 1). Differs from ISO weeks.
Which week does December 31 belong to?
December 31 can be Week 52, 53, or even Week 1 of next year! Under ISO 8601, if December 31 is Monday-Wednesday and most of that week falls in next year, it's Week 1 of the new year. Check calculator for specific year.
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