What week number is it?

Businesses across Europe and in manufacturing plan by week number rather than by date. This tool gives the ISO 8601 week for any date, shows the exact Monday-to-Sunday span, and also gives the simpler count some organisations use.

Pick a date

Result

October 23, 2026 is in ISO week 43 of 2026.

ISO week number
Week 43 of 2026
Week runs
October 19, 2026 to October 25, 2026
Weekday
Friday
Simple week number
Week 43 counting 1 January as week 1
Week of the month
4th
Quarter
Q4
Day of the year
296 of 365

How it is calculated

  • Under ISO 8601 a week starts on Monday and week 1 is the week that contains the first Thursday of the year — equivalently, the week containing 4 January.
  • Because of that rule, 1 January can fall in week 52 or 53 of the previous year, and 31 December can fall in week 1 of the next. The result shows which year the week belongs to.
  • The simple week number ignores all of that and counts blocks of seven days from 1 January, which is why the two figures often differ by one.
  • A year has 53 ISO weeks when it starts on a Thursday, or on a Wednesday in a leap year; otherwise it has 52.

Where this is used in the real world

  • Production and shipping schedules quoted as “week 34 delivery”.
  • European business planning, payroll periods and school terms.
  • Project management and sprint numbering.
  • Retail buying calendars that run in whole weeks rather than months.

Good to know

  • The United States and Canada often use a week that starts on Sunday and counts 1 January as week 1. That is the simple week number shown here, not the ISO number.
  • Because ISO weeks belong to the year containing their Thursday, a date in late December can legitimately be “week 1 of next year”.

Questions people ask

What is the current week number?

Open this page and the tool starts on today’s date, showing the ISO week and the Monday-to-Sunday range it covers.

Why does 1 January sometimes show week 52 or 53?

ISO weeks never split: the week containing 1 January belongs to whichever year holds its Thursday. If 1 January is a Friday, Saturday or Sunday, the week is the last week of the old year.

How many weeks are in a year?

Fifty-two in most years, and fifty-three in years that begin on a Thursday, or on a Wednesday when the year is a leap year.