⚡ Quick Answer

The week number tells you which week of the year a date falls in. ISO 8601 (used internationally) defines week 1 as the week containing the first Thursday of January. A year has 52 or 53 weeks. This is used in business, payroll, project planning, and scheduling worldwide.

📅 Daily Life

📆 Week Number Calculator

Find the week number for any date, or find what date a specific week number starts on. Used for business scheduling, payroll, project planning, and international date systems.

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🦉Owl's Explanation

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🤔 How Does This Work?

Our Week Number Calculator uses the ISO 8601 standard for week numbering:

Weeks start on Monday and end on Sunday
Week 1 is the week containing the first Thursday of the year
To find week number: find the nearest Thursday to the date, then count weeks from January 1
To find week start date: find the Monday of the ISO week by working backwards from the Thursday rule

This is the most widely used international standard for week numbering, used in business, payroll, and project management worldwide.

✅ Trusted Tool

The 365tool.net Week Number Calculator uses the ISO 8601 international standard for week numbering — the same system used by most businesses and governments worldwide. Free for HR teams, project managers, businesses, and students. No sign-up needed.

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❓ FAQ

What is ISO week numbering?▼

ISO 8601 is the international standard for week numbering. Week 1 is the week containing the year's first Thursday. Weeks run Monday to Sunday. Most businesses, especially in Europe, use ISO week numbers for scheduling and reporting.

What week number is it today?▼

Enter today's date in our Week Number Calculator and it instantly shows the ISO week number. Alternatively, our calculator automatically sets today's date when the page loads.

Does a year always have 52 weeks?▼

Most years have 52 weeks plus 1 or 2 extra days. Some years have 53 ISO weeks — this happens when January 1 falls on a Thursday, or on a Wednesday in a leap year. The last week of the year can be week 52 or 53.

How do businesses use week numbers?▼

Businesses use week numbers for payroll periods, project timelines, sales reporting, and inventory management. 'Deliver by week 12' is clearer than 'deliver by the third week of March' because week numbers are unambiguous.

How do I find what date week 1 starts?▼

Week 1 starts on the Monday of the week containing the first Thursday of January. Our calculator can find the exact start and end dates for any week number in any year.

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