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2026 week numbers

2026 has 53 ISO weeks.

Week 1 runs December 29 to January 4, and week 53 ends January 3. Weeks run Monday to Sunday, following ISO 8601.

Weeks
53
Week 1 starts
December 29
Week 53 ends
January 3
Standard
ISO 8601
ISO week numbers for 2026
WeekStarts (Monday)Ends (Sunday)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53

Why 2026 has 53 weeks

Under ISO 8601 a week belongs to the year that contains its Thursday. That gives every year either 52 or 53 whole weeks and never splits one across a year boundary. A year gets 53 when it starts on a Thursday, or on a Wednesday in a leap year.

This is why week 1 of 2026 begins on Monday, December 29, 2025 — in the previous calendar year. It is also why week 53 runs to Sunday, January 3, 2027, ending in the following year.

ISO weeks versus US week numbering

The two conventions disagree. ISO weeks start on Monday, and week 1 is the week holding the first Thursday. The common North American convention starts weeks on Sunday and calls the week containing 1 January week 1, which can produce a short first week. Payroll, retail, and broadcast calendars often use the latter. If a week number here disagrees with one from another system, this is usually why.

Week numbers by month

Each month page shows the ISO weeks it spans:

Other years

Common questions

How many weeks are in 2026?
2026 has 53 ISO weeks. A year has 53 rather than 52 when it begins on a Thursday, or begins on a Wednesday in a leap year; otherwise it has 52.
When does week 1 of 2026 start?
Week 1 of 2026 runs from Monday, December 29, 2025 to Sunday, January 4, 2026. Under ISO 8601, week 1 is the week containing the first Thursday of the year, which is why it starts in 2025.
Do week numbers start on Monday or Sunday?
ISO 8601 weeks start on Monday and end on Sunday. This differs from the common North American convention, where weeks start on Sunday and week 1 is simply the week containing 1 January — so a week number here may not match one from a US payroll or retail system.