What Week Number Is It?

Choose a date to get its ISO 8601 week number, used across the UK and Europe, with the dates of that week’s Monday and Sunday.

Week numbers 2026

2026 has 53 weeks. The current week is highlighted.

Frequently asked questions

What week number is it today?

Today is week 41 of 2026, from Monday 5 to Sunday 11 October 2026. The calculator always opens on today’s date.

How many weeks are there in a year?

Usually 52, sometimes 53, as in 2020, 2026 and 2032. A 365-day year is 52 weeks and 1 day. That extra day gradually shifts the weeks, so a week 53 comes round every 5 or 6 years.

Does week 1 always start in January?

No. It starts on the Monday of the week containing 4 January, and that Monday can fall anywhere between 29 December and 4 January. In 2026, week 1 began on Monday 29 December 2025.

Why does my calendar show a different number?

Some calendars use the US system or start the week on Sunday. In your calendar settings, set Monday as the first day of the week and, if available, choose the ISO week numbering (in Outlook: first week of year “First 4-day week”).

How the week number is calculated

The UK, like the rest of Europe, numbers weeks according to the international standard ISO 8601:

• A week starts on Monday and ends on Sunday.
• Week 1 is the week containing the first Thursday of the year, which is also the week containing 4 January.
• A year therefore has 52 or 53 weeks.

The first days of January can belong to the last week of the previous year, and the last days of December to week 1 of the next year. For example, Friday 1 January 2027 belongs to week 53 of 2026.

To calculate it, find the Thursday of the week the date falls in: the year of that Thursday is the week’s year, and its position in the year gives the number.

Week = whole part of ((day of the year of the Thursday − 1) ÷ 7) + 1

Why 2026 has 53 weeks

A year has 53 weeks when it starts on a Thursday, or on a Wednesday in a leap year. 1 January 2026 was a Thursday, so the year has 53 weeks: week 1 began on Monday 29 December 2025 and week 53 ends on Sunday 3 January 2027. The next years with 53 weeks are 2032 and 2037.

In Excel

The ISOWEEKNUM(date) function returns the ISO 8601 week number, as does WEEKNUM(date,21). Be careful with WEEKNUM(date) without a second argument: it starts weeks on Sunday and counts the week containing 1 January as week 1, which sometimes gives a different number.

Other countries

In the United States and some other countries, weeks usually start on Sunday and week 1 is the one containing 1 January. When working with international teams, give the date of the Monday as well as the week number.

More date calculators

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• Working daysMonday to Friday, with bank holidays in England and Wales excluded.
• Add days to a dateThe exact date in 30, 60 or 90 days, or counting back.
• Age calculatorExact age in years, months and days, plus your 10,000th day.
• CountdownHow many days until Christmas, Easter or any date you choose.