What Week Is It? Week Number Calculator

What week is it? The calculator shows today’s week number in your time zone, using the ISO 8601 standard (weeks start on Monday) and the U.S. Sunday-start numbering, plus the week of any date you choose. Below it, a table lists every week of the year with its dates.

ISO week numbers vs. U.S. week numbers

• ISO 8601: weeks run Monday to Sunday and week 1 is the week with the year’s first Thursday. Used in most of Europe, in many payroll and planning systems, and by Excel’s ISOWEEKNUM.
• U.S. (Sunday start): weeks run Sunday to Saturday and week 1 is the week of January 1. This is what Excel’s WEEKNUM returns by default.
• The two can differ by one week, especially in early January and late December.

Years with 53 weeks

A year has 52 ISO weeks, or 53 when it starts on a Thursday — or on a Wednesday in a leap year. 2026 has 53 ISO weeks; the next years with 53 are 2032 and 2037. In a 53-week year, weekly payroll has 53 paydays if payday falls on the extra week’s day.

Frequently asked questions

What week of the year is it?

The calculator at the top shows today’s ISO week number and its Monday-to-Sunday dates, updated in your time zone.

How many weeks are in a year?

52 weeks and 1 day (2 in a leap year). In ISO numbering a year has 52 or 53 weeks; 2026 has 53.

When does week 1 start?

In ISO 8601, week 1 is the week (Monday to Sunday) that contains the first Thursday of the year, which is also the week with January 4. On U.S. calendars, week 1 is the week of January 1.

Is the ISO week number the same as Excel’s WEEKNUM?

Not always. Excel’s ISOWEEKNUM returns the ISO week; WEEKNUM with its default setting uses Sunday-start weeks with week 1 on January 1, the U.S. number shown here.

What day of the year is it?

The calculator shows the day of the year (1 to 365, or 366 in a leap year) and how many days are left.