Frequently Asked Questions

What is a week number?

A week number indicates which week of the year a specific date falls in. Weeks are numbered from 1 to 52 (or 53) based on the ISO week date system.

How is week number calculated?

Week numbers follow ISO 8601 standard. Week 1 is the week with the first Thursday of the year. Weeks start on Monday and end on Sunday.

What is ISO week date?

ISO week date format is YYYY-Www-D, where YYYY is year, Www is week number (with leading zero), and D is day of week (1=Monday to 7=Sunday).

Why are there 53 weeks sometimes?

Some years have 53 weeks when the year starts on a Thursday (in leap years) or a Wednesday (in common years) in the ISO week system.

When does week 1 start?

Week 1 is the week that contains the first Thursday of the year. This means week 1 can start as early as December 29 of previous year.

Is this calculator free?

Yes! 100% free. No registration, no hidden costs. Use it for all your week number calculations.

week number week calculator week of year ISO week calendar week date to week

Week Number Calculator - Find Any Date's Week

Our Week Number Calculator PRO helps you find the exact week number of any date according to the ISO 8601 standard. Whether you're planning projects, tracking deadlines, or just curious about the week, this tool provides instant results.

Features: Get week number, ISO week date (YYYY-Www-D), week start and end dates, day of year, remaining days, year progress percentage, and visual week grid. Perfect for project planning, academic schedules, and business planning.

Perfect for: Project managers, students, teachers, event planners, businesses, and anyone needing to organize by week numbers.