caldays
Week numbers 2026

How many weeks in 2026? 53 weeks.

2026 has 53 ISO 8601 weeks. Week 1 starts on the Monday of the week that contains the first Thursday of January. Use this page to look up any week number for 2026, 2027, or any historical year.

ISO 8601

The international week-number standard

ISO 8601 defines how weeks are numbered worldwide. The rule: week 1 of a year is the week containing the first Thursday of January — or equivalently, the week containing January 4.

Weeks start on Monday and end on Sunday. A year can have either 52 or 53 ISO weeks. Years with 53 weeks always start or end on a Thursday — or are leap years starting/ending on Wednesday.

This is the standard used in business, logistics, manufacturing, and finance throughout Europe, parts of Asia, and increasingly in global software (it's the default in Python's `isocalendar()`, JavaScript libraries like date-fns, and PostgreSQL).

Quick reference

Each week of 2026

W01
29 Dec – 4 Jan
W02
5 Jan – 11 Jan
W03
12 Jan – 18 Jan
W04
19 Jan – 25 Jan
W05
26 Jan – 1 Feb
W06
2 Feb – 8 Feb
W07
9 Feb – 15 Feb
W08
16 Feb – 22 Feb
W09
23 Feb – 1 Mar
W10
2 Mar – 8 Mar
W11
9 Mar – 15 Mar
W12
16 Mar – 22 Mar
W13
23 Mar – 29 Mar
W14
30 Mar – 5 Apr
W15
6 Apr – 12 Apr
W16
13 Apr – 19 Apr
W17
20 Apr – 26 Apr
W18
27 Apr – 3 May
W19
4 May – 10 May
W20
11 May – 17 May
W21
18 May – 24 May
W22
25 May – 31 May
W23
1 Jun – 7 Jun
W24
8 Jun – 14 Jun
W25
15 Jun – 21 Jun
W26
22 Jun – 28 Jun
W27
29 Jun – 5 Jul
W28
6 Jul – 12 Jul
W29
13 Jul – 19 Jul
W30
20 Jul – 26 Jul
W31
27 Jul – 2 Aug
W32
3 Aug – 9 Aug
W33
10 Aug – 16 Aug
W34
17 Aug – 23 Aug
W35
24 Aug – 30 Aug
W36
31 Aug – 6 Sep
W37
7 Sep – 13 Sep
W38
14 Sep – 20 Sep
W39
21 Sep – 27 Sep
W40
28 Sep – 4 Oct
W41
5 Oct – 11 Oct
W42
12 Oct – 18 Oct
W43
19 Oct – 25 Oct
W44
26 Oct – 1 Nov
W45
2 Nov – 8 Nov
W46
9 Nov – 15 Nov
W47
16 Nov – 22 Nov
W48
23 Nov – 29 Nov
W49
30 Nov – 6 Dec
W50
7 Dec – 13 Dec
W51
14 Dec – 20 Dec
W52
21 Dec – 27 Dec
W53
28 Dec – 3 Jan

Frequently asked questions

How many weeks are in 2026?
2026 has 53 ISO 8601 weeks.
When does ISO week 1 start?
The week containing January 4 — or equivalently, the week containing the first Thursday of January. Weeks always start Monday and end Sunday.
What's the difference between ISO weeks and US weeks?
In the US system, week 1 is the week containing January 1, and weeks typically start on Sunday. This means the same calendar day can have different week numbers depending on which system you use.
How do I find the week number for a specific date?
Use the date calculator at /date-calc/weekday — enter any date and we'll show its ISO week number, day of year, and weekday.
Why do some years have 53 weeks?
Because 365 ÷ 7 = 52 remainder 1, an extra day floats around each year. Years that start or end on Thursday (or leap years starting on Wednesday) accumulate that extra day into a 53rd week.
Other years

Week numbers in other years

Explore more

Week numbers
2026 has 53 ISO weeks