Week Number to Date: How to Find ISO Week Dates
Convert an ISO week number into its Monday-to-Sunday calendar date range.
Quick answer
To convert an ISO week number to dates, choose the ISO week-year and week number. The result is the Monday-to-Sunday date range for that ISO week.
What week number to date means
A week number such as Week 30, 2026 is useful as a short planning label, but it is not always enough on its own. The week-number-to-date calculation converts that label into real calendar dates so you can see when the week starts and ends.
In the ISO system, every week starts on Monday and ends on Sunday. That means the result for an ISO week number is always a seven-day date range, not an approximate period.
Why the ISO week-year matters
Always use the ISO week-year together with the week number. Around New Year, a date can belong to a different ISO week-year than its calendar year. This is why Week 1 and Week 52 or 53 should be checked with the correct year.
For example, a late December date can sometimes belong to Week 1 of the next ISO year, while an early January date can sometimes belong to the final ISO week of the previous ISO year.
How to use the calculator
Open the Weeks Calculator, choose Week number to date, select the ISO week-year and the ISO week number, then press Find dates. The result shows the full week range and links to the same week in the yearly calendar.
The weekday dropdown is optional. Use it only when you need the exact date for a specific day inside the selected ISO week.
FAQ
Do ISO week date ranges always start on Monday?
Yes. ISO week date ranges start on Monday and end on Sunday.
Can I enter week 53 for any year?
No. Only some ISO years have week 53. If a year has only 52 ISO weeks, the calculator will show a validation message.
Related guides
What Week Is It Today?
Find the current ISO week number and see how week numbers help with planning.
Week Number Today
See today’s ISO week number and how it applies to schedules, reports, and planning.
ISO Week Number Explained
A clear explanation of ISO weeks, week-years, and the rule that defines week 1.