How to Calculate Week Number

What is Week Number?

A week number calculator determines the ISO 8601 week number for any date (1–53). ISO weeks start on Monday; week 1 contains the year's first Thursday. Week numbering is widely used in manufacturing schedules, project planning, and European business contexts.

Step-by-Step Guide

1. 1Input a date
2. 2Calculate ISO week number
3. 3Show first/last day of week

Worked Examples

Common Mistakes to Avoid

• ✕Not double-checking results
• ✕Ignoring edge cases

Frequently Asked Questions