Week Number Calculator: The Complete Guide
Find the week number for any date. Enter a date to see its ISO-8601 week number, which day of the year it is, and which day of the week — handy for planners, payroll, and project scheduling.
Who the Week Number Calculator is for
Planners and professionals who work in week numbers for scheduling, payroll, or manufacturing.
How to use the Week Number Calculator
- Type your values into the fields above — pick your currency or units where the calculator offers them.
- Results update automatically as you type; there's no submit button and nothing is sent to a server.
- Adjust any input to compare scenarios, then copy the result with a single click.
How it works
ISO-8601 weeks start on Monday, and week 1 is the week containing the year's first Thursday. The day of the year counts from 1 January as day 1.
Features
- ISO-8601 week number
- Day of the year
- Day of the week
- Any date
What is an ISO week number?
The ISO-8601 standard numbers the weeks of the year 1 to 52 or 53, with each week starting on Monday and week 1 being the one that contains the first Thursday. Many industries — manufacturing, logistics, and European business — schedule by week number, so converting a date to its week is a common need.