Week Numbers UK
Today is week 42 of 2026 (12 October to 18 October).
Today's week number, with the start and end date of the week. You can also browse all weeks of a year or the yearly calendar with week numbers.
Week number today
Calculating today's week number…
How do week numbers work?
Most of the world uses the ISO-8601 standard: weeks start on Monday and week 1 is the week with the first Thursday of the year. A year can therefore start in week 52 or 53 of the previous year.
What is a week number?
A week number tells you which week of the year a date falls in. Instead of writing out a whole period, you simply give the number: the week from 12 October to 18 October, for example, is week 42.
Week numbers are widely used in business in the United Kingdom, especially in logistics, manufacturing, retail and project planning. You'll find them in diaries, on rotas, in delivery schedules and in planning software.
How does ISO week numbering work?
In the United Kingdom, week numbers follow the international standard ISO 8601, the same system used across Europe. It has three rules. A week starts on Monday and ends on Sunday. Every week belongs entirely to one year. And week 1 is the week containing the first Thursday of January, which is always also the week containing 4 January.
Because of that last rule, New Year can produce surprises. If the year starts on a Friday, Saturday or Sunday, the first days of January still belong to the last week of the old year. If it starts on a Tuesday, Wednesday or Thursday, the last days of December already fall in week 1 of the new year. So for dates around New Year, check which year goes with the week number.
Why does a year sometimes have 53 weeks?
A year is slightly longer than 52 weeks: 52 weeks and one day, or 52 weeks and two days in a leap year. Those extra days add up, and every so often that produces a week 53. Under ISO 8601 this happens when a year starts on a Thursday, or when a leap year starts on a Wednesday. On average that's about once every five to six years.
2026 has 53 weeks. The next year with a week 53 is 2032.
What are week numbers used for?
Week numbers are especially useful when you plan in weeks rather than dates. Suppliers agree delivery weeks, production and construction schedules run week by week, and many shift rotas and payroll cycles are organised by week. Teams that work with colleagues in mainland Europe will notice that week numbers are used there even more often than in the UK.
Many retailers also work with their own trading calendar, with a financial year split into weeks that doesn't always match the calendar year. In that case the week number in your company's systems can differ from the ISO week number shown here.
US week numbers are different
Weeks are not counted the same way everywhere. In the United States, a week starts on Sunday and week 1 is the week containing 1 January, however short that week is. As a result, the American week number can be one week different from the ISO week number. If you work with American colleagues or use American software, check which system is being used.
Excel has the same difference: the WEEKNUM function counts from Sunday by default, while ISOWEEKNUM follows the ISO standard you see on this site.
Frequently asked questions
What week number is it today?
It is week 42 of 2026, from 12 October to 18 October. The week number at the top of this page updates in your browser and follows the ISO-8601 week numbering used in the UK and most of Europe.
When does week 1 start?
Week 1 is the week containing the first Thursday of the year. Weeks always start on Monday and end on Sunday.
Can I print or download the week numbers?
Yes. Every year page lets you print the week numbers, download them as an Excel file or save them as a PDF.
How many weeks are there in 2026?
2026 has 53 weeks under ISO-8601 week numbering. The next year with 53 weeks is 2032.
Why is there sometimes a different year next to the week number?
An ISO week always belongs entirely to one year: the year in which the Thursday of that week falls. Around New Year, a week can therefore belong to the previous or the next year. That's why we show the ISO year alongside the week number.