What Week Is It? — Week Number Calculator (ISO Week)

What week number is it?

The ISO week number for today or any date you choose, with the date range of that week, the US-style week number and the day of the year.

Week number calculator

ISO week number

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ISO week numbers 2026 and 2027

ISO 8601 weeks start on Monday, and week 1 is the week that contains the year's first Thursday. 2026 has 53 weeks, 2027 has 52.

Week	2026	2027
1	Dec 29 – Jan 4	Jan 4 – Jan 10
2	Jan 5 – Jan 11	Jan 11 – Jan 17
3	Jan 12 – Jan 18	Jan 18 – Jan 24
4	Jan 19 – Jan 25	Jan 25 – Jan 31
5	Jan 26 – Feb 1	Feb 1 – Feb 7
6	Feb 2 – Feb 8	Feb 8 – Feb 14
7	Feb 9 – Feb 15	Feb 15 – Feb 21
8	Feb 16 – Feb 22	Feb 22 – Feb 28
9	Feb 23 – Mar 1	Mar 1 – Mar 7
10	Mar 2 – Mar 8	Mar 8 – Mar 14
11	Mar 9 – Mar 15	Mar 15 – Mar 21
12	Mar 16 – Mar 22	Mar 22 – Mar 28
13	Mar 23 – Mar 29	Mar 29 – Apr 4
14	Mar 30 – Apr 5	Apr 5 – Apr 11
15	Apr 6 – Apr 12	Apr 12 – Apr 18
16	Apr 13 – Apr 19	Apr 19 – Apr 25
17	Apr 20 – Apr 26	Apr 26 – May 2
18	Apr 27 – May 3	May 3 – May 9
19	May 4 – May 10	May 10 – May 16
20	May 11 – May 17	May 17 – May 23
21	May 18 – May 24	May 24 – May 30
22	May 25 – May 31	May 31 – Jun 6
23	Jun 1 – Jun 7	Jun 7 – Jun 13
24	Jun 8 – Jun 14	Jun 14 – Jun 20
25	Jun 15 – Jun 21	Jun 21 – Jun 27
26	Jun 22 – Jun 28	Jun 28 – Jul 4
27	Jun 29 – Jul 5	Jul 5 – Jul 11
28	Jul 6 – Jul 12	Jul 12 – Jul 18
29	Jul 13 – Jul 19	Jul 19 – Jul 25
30	Jul 20 – Jul 26	Jul 26 – Aug 1
31	Jul 27 – Aug 2	Aug 2 – Aug 8
32	Aug 3 – Aug 9	Aug 9 – Aug 15
33	Aug 10 – Aug 16	Aug 16 – Aug 22
34	Aug 17 – Aug 23	Aug 23 – Aug 29
35	Aug 24 – Aug 30	Aug 30 – Sep 5
36	Aug 31 – Sep 6	Sep 6 – Sep 12
37	Sep 7 – Sep 13	Sep 13 – Sep 19
38	Sep 14 – Sep 20	Sep 20 – Sep 26
39	Sep 21 – Sep 27	Sep 27 – Oct 3
40	Sep 28 – Oct 4	Oct 4 – Oct 10
41	Oct 5 – Oct 11	Oct 11 – Oct 17
42	Oct 12 – Oct 18	Oct 18 – Oct 24
43	Oct 19 – Oct 25	Oct 25 – Oct 31
44	Oct 26 – Nov 1	Nov 1 – Nov 7
45	Nov 2 – Nov 8	Nov 8 – Nov 14
46	Nov 9 – Nov 15	Nov 15 – Nov 21
47	Nov 16 – Nov 22	Nov 22 – Nov 28
48	Nov 23 – Nov 29	Nov 29 – Dec 5
49	Nov 30 – Dec 6	Dec 6 – Dec 12
50	Dec 7 – Dec 13	Dec 13 – Dec 19
51	Dec 14 – Dec 20	Dec 20 – Dec 26
52	Dec 21 – Dec 27	Dec 27 – Jan 2
53	Dec 28 – Jan 3	—

How is it calculated?

In the ISO 8601 system used in Europe and much of the world, weeks start on Monday and week 1 is the week with the year's first Thursday. Some years therefore have 53 weeks, and early January can belong to the previous year's last week.

In the US, weeks are usually counted from Sunday and week 1 is the week containing 1 January.

Common questions

How many weeks does a year have?

52 or 53 ISO weeks. A year has 53 weeks if it starts on a Thursday, or on a Wednesday in a leap year.

Why does my calendar show a different week number?

It probably uses the US system (weeks starting Sunday). Both numbers are shown above.