What Week Is It? Week Number Today

See today’s ISO week number, the first and last day of the week, and the full list of weeks of the year with their dates. Enter your values; the result updates as you type, with the method shown below.

About this calculator

Week numbers are used in business, schools, logistics and planning, especially in Europe. This calculator gives the ISO week number of any date, with its first and last days, and the number of weeks in the year.

Enter a date. The calculator shows the ISO week number, the Monday and Sunday of that week and whether the year has 52 or 53 weeks.

When to use it

  • Planning deliveries or production by week.
  • Matching a European planning calendar.
  • Booking holidays expressed in weeks.
  • Understanding a week number on an invoice.

How to read the result

ISO weeks start on Monday. Week 1 is the week containing the first Thursday of January, so 1 to 3 January can belong to the last week of the previous year.

A year has 53 ISO weeks when it starts on a Thursday, or on a Wednesday in a leap year.

Mistakes to avoid

  • Using the US system, where weeks start on Sunday.
  • Assuming 1 January is always in week 1.
  • Forgetting years with 53 weeks.

Formula

ISO 8601 week (Monday start, week 1 contains 4 January)

Worked example

8 November 2026 is in week 45 (2 to 8 November).

Frequently asked questions

How are weeks counted?

ISO 8601: weeks start on Monday and week 1 contains the first Thursday of the year.

Can a year have 53 weeks?

Yes, when it starts or ends on a Thursday.

Another date?

Change the date field.

Which week system is used?

ISO 8601, the standard in Europe.

Why does my calendar show a different number?

It may use the US system starting on Sunday.

Which years have 53 weeks?

For example 2026 and 2032.

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Results are estimates for information only. Check important figures with a professional.