Find the ISO week number (1–53) for any date.
ISO week numbers are used extensively in business, project management, logistics, and some payroll systems — particularly in European business culture where 'Week 32' is a more natural way to reference a time period than 'the first week of August'.
Enter any date and this tool returns its ISO week number, the day of the week, and the start and end dates of that week. You can also look up any week number to find its corresponding dates.
Useful for timesheet completion, project scheduling, confirming which week a particular date falls in for reporting purposes, and interpreting dates in documents that use week numbers.
The ISO 8601 standard defines weeks as running Monday to Sunday. Week 1 of any year is the week containing the first Thursday of January (equivalently, the week containing January 4). This means some years have 52 weeks and others have 53, and January 1 may fall in Week 52 or 53 of the previous year.
Under ISO 8601, if January 1 falls on a Friday, Saturday, or Sunday, that day belongs to the last week of the previous year because the majority of that week (Monday-Wednesday) falls in December. This is counterintuitive but mathematically consistent.
The current week number is shown automatically when you open this page. Today is in the week shown in the result.