Week Number Calculator
The Week Number Calculator finds the ISO week number for any date, or shows which dates fall within a given week number - handy for business and project scheduling.
What ISO week numbers are
Many businesses, especially in Europe and manufacturing, schedule by week number ("we ship in week 32") rather than exact dates. The ISO 8601 standard numbers weeks 1–52 (occasionally 53), with weeks starting on Monday and week 1 being the one containing the year's first Thursday. This tool converts between any date and its ISO week.
Both directions
Enter a date to get its week number, or enter a week number and year to see the Monday-to-Sunday date range it covers. It removes the guesswork when coordinating with teams or suppliers who plan by week. For general date gaps, see the Date Duration Calculator.
Frequently Asked Questions
What is an ISO week number?
Under ISO 8601, weeks start on Monday and week 1 is the week containing the year's first Thursday, numbering the weeks 1 to 52 or 53.
Why do businesses use week numbers?
They simplify scheduling and coordination, especially in manufacturing and across regions, by referring to "week 32" instead of a date.
Can it show the dates in a given week?
Yes. Enter a week number and year to see the Monday-to-Sunday date range it covers.
Can a year have 53 weeks?
Yes. Some years contain 53 ISO weeks, depending on how the days fall, which the calculator accounts for.
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