📆 Week Number Finder

What Is an ISO Week Number?

The ISO 8601 standard defines weeks as starting on Monday and ending on Sunday. Each week is assigned a number from 1 to 52 (or 53 in long years). Week 1 is the week that contains the first Thursday of January. This system is widely used in business, manufacturing, and government for scheduling and reporting.

How to Use the Week Number Finder

• Pick a date — Use the date picker to select any date
• Click "Today" — Instantly see the current week number
• Read the results — The ISO week number and corresponding ISO year are displayed

Why Week Numbers Matter

• Project planning — Many organizations plan by week number (e.g., "delivery in W23")
• Manufacturing — Production schedules are often organized by work week
• Reporting — Weekly reports are typically identified by their week number
• Payroll — Some companies process payroll by week number
• Academic calendars — Universities often reference week numbers in syllabi

ISO Week Number Rules

• Weeks start on Monday and end on Sunday
• Week 1 contains the first Thursday of January
• A year can have 52 or 53 weeks (53 in years where Jan 1 is a Thursday, or Dec 31 is a Thursday)
• The ISO year may differ from the calendar year for dates near January 1 or December 31

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