Week Number Calculator
Check this week number or calculate the week number for any date with ISO and Sunday-start ranges.
Concept
Week number depends on the chosen start of week
This week number calculator returns the week index for a date and shows the matching week range.
A week number is a label for a date, and the same date can map to different week numbers when the rule changes. This tool supports ISO 8601 Monday-start weeks and Sunday-start weeks.
You can check this week at a glance or test a specific date, then compare how ISO week and Sunday-start results differ in week boundaries and year transitions.
Current week lookup
Use today or any selected date to quickly check which week it belongs to.
ISO Week vs Sunday start
Use both options when your schedule depends on international standards or local weekly reports.
Cross-year handling
Dates at year-end or year-start can belong to the previous or next ISO week, so always confirm the year context.
This calculator only computes week number and week range for the chosen rule; other schedule logic should be handled by your planning system.
Week Number Calculator Week number workspace
How to use
- 1 Choose today or enter the date you want to check.
- 2 Select ISO Monday-start or Sunday-start week numbering.
- 3 Calculate the week number, review the week range, and copy the result.
Common use cases
- What week number is it today?
- ISO week number for a specific date
- Week count with Monday or Sunday start
Frequently asked questions
Which week numbering rules can I choose?
Enter a date and choose either ISO week numbering with Monday as the week start, or Sunday-start week numbering.
Can I check this week's number?
Yes. Use today's date to see the current week number, or choose another date to calculate its week number.
What does the result show besides the week number?
The result shows the calculated week and the start and end dates of that week for the selected rule. You can copy the result text.
How are dates near the start or end of a year shown?
With Monday-start ISO rules, year-end or year-start dates may belong to a week in the previous or next year. Sunday-start mode calculates against the date's calendar year.