Week Number Calculator
Find ISO week numbers and date ranges
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Find Week Number from Date
Find Date Range from Week Number
Week Start (Monday)
2025-12-29
Week End (Sunday)
2026-01-04
How to Use Week Number Calculator
- 1See the current week number automatically.
- 2Enter a date to find its week number.
- 3Enter a week number to find its date range.
- 4View year progress and weeks remaining.
About Week Number Calculator
Find the ISO week number for any date, or find the date range for any week number. Shows the current week number, weeks remaining in the year, and year progress.
Frequently Asked Questions
What is ISO week numbering?
ISO 8601 defines week 1 as the week containing the first Thursday of the year. Weeks start on Monday. A year has 52 or 53 weeks.
Why do some years have 53 weeks?
Years that start on Thursday (or Wednesday in leap years) have 53 ISO weeks. This happens roughly every 5-6 years.