Week Number to Date Calculator
Enter an ISO week number and year to find that week's exact Monday–Sunday date range.
How this is calculated
ISO 8601 defines week 1 of a year as the week containing that year's first Thursday, with every week running Monday to Sunday. This calculator finds week 1's Monday, then counts forward seven days at a time to the week you entered — the exact reverse of the math the Week Number Calculator uses to turn a date into a week number.
Who actually needs this
Software teams running two-week sprints numbered by ISO week, manufacturers reading a "week 23" date code off a production label, and payroll or fiscal systems in Europe that report by week rather than by month all eventually need to turn that bare week number back into an actual calendar date range. Because the US mostly doesn't use ISO week numbers day to day, the conversion isn't something most people memorize — this tool does the lookup instead of you counting seven-day blocks by hand.
Frequently asked questions
How do I convert a week number back into a date?
Enter the year and the ISO week number (1–52, or 1–53 in years that have one). The calculator returns that week's Monday start date and Sunday end date.
What if I enter week 53 for a year that only has 52 weeks?
The calculator flags it and shows the correct maximum week number for that year instead of returning a date outside the year's actual ISO calendar.
Does the week start on Monday or Sunday?
Monday, per the ISO 8601 standard. That's why the date range shown always runs Monday through Sunday, even though the US commonly treats Sunday as the first day of the week.