Small Things Sorted

Find the week number

Which week is this date in – and what dates are in week 34?

Following ISO 8601: the week starts on Monday, and the first week of the year is the one containing the first Thursday.

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How to do it

  1. Choose a direction

    Week number for a date, or dates for a week number.

  2. Enter your value

    A date, or a week and a year.

  3. Read the range

    Monday to Sunday, with the year the week belongs to.

What this is for

Week numbers are everyday currency in European project plans, delivery dates and holiday requests. The rule behind them is less simple than it looks: under ISO 8601 the week starts on Monday, and the first week of the year is the one containing the first Thursday.

That Thursday rule is why 1 January can still belong to the last week of the previous year – and why some years have 53 weeks. Both cases are shown rather than quietly rounded away.

A note for readers in the United States: the numbering there usually starts the week on Sunday and counts differently. This tool follows ISO 8601 throughout.

Common questions

Because the week containing it has its Thursday in the old year. That is the ISO rule, not a mistake.

Yes. It is shown when it happens.

No. In the United States the week usually starts on Sunday and week one is the one containing 1 January. This tool follows ISO 8601, as is customary in Europe.

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