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ISO 8601 week number

What week is it?

Today is

It is week

46

Week 46 of 2026 runs from to .

ISO week date
2026-W46-5
Weeks in 2026
53
Weeks left after this
7
Day of year
317 of 365
  1. Mon
  2. Tue
  3. Wed
  4. Thu
  5. Fri
  6. Sat
  7. Sun

Based on Coordinated Universal Time (UTC); updates to your time zone when the page loads. Weeks start on Monday, as defined by ISO 8601.

Find the week number for any date

Friday 13 November 2026 is in week 46 of 2026 (9 Nov 2026 – 15 Nov 2026), ISO week date 2026-W46-5.

All 53 weeks of 2026

Full Monday–Sunday tables: 2026 calendar with week numbers · 2027 calendar with week numbers

How ISO week numbers work

The week number shown above follows the international standard ISO 8601. Every ISO week starts on Monday and ends on Sunday, and every week belongs to exactly one year. Week 1 is the week containing the first Thursday of the year, which is the same as the week containing 4 January.

Because the year is assigned by the Thursday, the first days of January can belong to the last week of the previous year, and the last days of December can belong to week 1 of the next year. For example, 1–3 January 2027 belong to week 53 of 2026, while 29–31 December 2025 belonged to week 1 of 2026.

52 or 53 weeks?

Most years have 52 ISO weeks. A year has 53 weeks when it starts on a Thursday, or when it is a leap year that starts on a Wednesday. 2026 starts on a Thursday and has 53 weeks; 2027 has 52. A simple check: the week containing 28 December is always the last week of the year.

When does the week number change?

The week number changes at midnight between Sunday and Monday in your local time. Around that moment, people in different time zones can be in different weeks, so this page uses your device's time zone once it loads.

Other week-numbering systems

ISO week numbers are widely used in Europe, including the Nordic countries, for work schedules, school planning and deliveries. Some calendars, including many in the United States, start the week on Sunday and count the week containing 1 January as week 1. Those numbers can differ from ISO weeks, so check which system a schedule uses. In spreadsheets, =ISOWEEKNUM(date) returns the ISO week number.

Need to count days instead? Use the date calculator, or see the current time anywhere with the world clock.

Week number FAQ

What week number is it today?
This page shows the current ISO 8601 week number based on the date in your device's time zone. ISO weeks start on Monday and end on Sunday, so the number changes at midnight between Sunday and Monday local time.
When does week 1 start?
ISO week 1 is the week that contains the first Thursday of the year. Equivalently, it is the week that contains 4 January. Week 1 of 2026 started on Monday 29 December 2025, and week 1 of 2027 starts on Monday 4 January 2027.
How many weeks are in 2026 and 2027?
2026 has 53 ISO weeks; week 53 runs from Monday 28 December 2026 to Sunday 3 January 2027. 2027 has 52 ISO weeks.
Why does 1 January sometimes belong to week 52 or 53?
An ISO week belongs to the year that contains its Thursday. If 1 January falls on a Friday, Saturday or Sunday, that week's Thursday is in the previous year, so the date belongs to the last week of the previous ISO week-year. 1 January 2027 is a Friday and belongs to week 53 of 2026.
Is the week number the same in every country?
No. ISO 8601 week numbers are widely used in Europe, including the Nordic countries. Some other calendars, including many in the United States, start weeks on Sunday and count the week containing 1 January as week 1, so their numbers can differ from ISO week numbers, especially around New Year.
How do I get the ISO week number in Excel or Google Sheets?
Use =ISOWEEKNUM(date). Excel's WEEKNUM function uses a Sunday-start system by default; WEEKNUM(date, 21) returns the ISO week number.
What does a code like 2026-W45-1 mean?
It is the ISO 8601 week-date format: ISO week-year 2026, week 45, weekday 1 (Monday). Weekdays are numbered 1 for Monday through 7 for Sunday.