Convert Date to Week Number

What the result means

When you convert a date to a week number, you get more than just a number from 1 to 53. You also need the ISO week-year. This matters because dates near New Year can belong to an ISO year that is different from the calendar year.

For example, January 1 can sometimes be part of week 52 or 53 of the previous ISO year. Without the ISO year, a week number alone can be misleading.

Why conversion is useful

Date-to-week conversion is common in dashboards, timesheets, manufacturing plans, academic calendars and logistics. Many systems store events as dates but report activity by week. Converting the date allows those events to be grouped consistently.

It is also useful for personal planning. You might want to know which week contains a birthday, travel date, exam date or product release.

How this calculator helps

The calculator on this site converts dates directly in your browser. Choose a date, press the button, and the result shows the ISO week and week-year. No registration is required and the entered date is not sent anywhere.

For a wider view, open the yearly calendar and click a week number to see its start and end dates.

Example uses

A date-to-week conversion is helpful when you have a specific date but your organization reports by week number. For example, a delivery date can be converted into an ISO week so it fits neatly into a weekly operations report.

This is also useful for spreadsheet work. You can group individual dates by ISO week and compare workload, revenue, attendance or activity across consistent seven-day periods.

Important detail

Always include the ISO week-year with the result. Dates near January 1 can belong to the previous or next ISO year, so the week number alone is not always complete.