Calendar weeks
Week number calculator
Enter any date — in any year, past or future — and this calculator returns its ISO-8601 week number together with the Monday-to-Sunday range that week covers.
Any date works — past, present or future, in any year.
How to read the result
The large number is the ISO week number, and the line underneath it shows the exact dates of that week. A single date therefore belongs to one week that runs from Monday to Sunday, and it is always fully contained in one week number.
The year shown next to the week number is the ISO week year, which is not always the same as the calendar year printed on the date. If you pick a date in the first days of January or the last days of December, the week number and its year can belong to the neighbouring year.
When you need this
Week numbers are used for planning rather than for naming single days. A sprint that starts in week 12, a payroll period, a shipping slot described as "week 38", a school timetable or a manufacturing schedule are all easier to agree on as a week number than as an exact date, because everyone reads the same number.
Looking up which week a holiday, a deadline, a delivery date or a future appointment falls into is the most common reason to use a calculator. It also helps when a document refers to a week number and you need to know which days that really covers.
Which system is used here
This calculator follows ISO-8601, the international standard in which weeks start on Monday and week 1 is the week containing the first Thursday of January. That is the numbering used across Europe, in business and in most software. The United States commonly numbers weeks from Sunday with week 1 starting on January 1, so the same date can return a different number there — this tool always uses the ISO system.
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