📅 Week Number Calculator
Find the ISO week number for any date and convert between dates and week numbers.
About Week Number Calculator
Calculate ISO 8601 week numbers for any date. Find what week of the year a date falls in, or find all dates in a given week number. Useful for project planning, academic calendars, and business reporting.
Features
- Date to week number
- Week number to dates
- ISO 8601 standard
Frequently Asked Questions
What is ISO week number?
ISO 8601 defines week numbers where week 1 is the week containing the first Thursday of the year. Weeks start on Monday and are numbered 1-52 or 1-53.
How many weeks in a year?
Most years have 52 weeks (364 days). Leap years and years starting on Thursday have 53 weeks. Our calculator handles all these edge cases.
Why use week numbers?
Week numbers are used in project management, manufacturing schedules, school calendars, payroll periods, and international business for standardized time planning.