Week Number Calculator: Find a Week of the Year
Find the week number for a date, or enter a week number to see its seven dates. Adjust the week-year start and numbering convention to match your calendar.
How week numbers are assigned
A week number depends on more than the date: a calendar needs a first weekday, a week-year boundary, and a rule for deciding which days belong to week 1. These settings can shift week numbers near the start and end of a year. Select the convention used by your workplace or organization.
Frequently asked questions
Why can week numbers differ between calendars?
Conventions vary: weeks may begin on Sunday or Monday, week 1 may contain January 1 or the first Thursday, and some calendars use a different week-year start.
Can I look up dates from a week number?
Yes. Switch to Week number, enter a week-year and week number, and the calculator returns the seven dates.
What are the week 1 options?
Week 1 can be the week containing the week-year start date, the first full week, or the first week with at least four days in that week-year.
What is the default convention?
The defaults follow ISO-style numbering: January start, Monday first, and week 1 is the first week with at least four days.