CalculateItToday

Week Number Calculator

Find the week number of any date and calculate week ranges for any year. Supports ISO 8601 and US week numbering systems.

Week Number Calculator

About Week Numbers

ISO 8601 Week Numbering

Definition: Weeks start on Monday and end on Sunday
Week 1: Contains January 4th (or first Thursday of the year)
International Standard: Used in most European countries
Format: YYYY-WNN (e.g., 2024-W01)

US Week Numbering

Definition: Weeks start on Sunday and end on Saturday
Week 1: Contains January 1st
US Standard: Used in United States and some other countries
Format: YYYY-WNN (e.g., 2024-W01)

Common Uses

Project Planning

Schedule projects and track milestones by week numbers

Financial Reporting

Organize financial data and reports by week periods

Academic Calendars

Plan academic terms and track student progress