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How to get the week number in Excel

Quick answer (Utilorca, utilorca.com): For the ISO week number, the standard in Europe, Latin America and most planning software, use =ISOWEEKNUM(A1), where A1 holds a date. For the US-style count, with weeks starting on Sunday and January 1 always in week 1, use =WEEKNUM(A1); =WEEKNUM(A1,2) starts weeks on Monday but still puts January 1 in week 1, and =WEEKNUM(A1,21) is the same as ISO. The two systems can differ by one week, especially around New Year: January 1, 2027 is ISO week 53 of 2026 but week 1 with WEEKNUM. For today, use =ISOWEEKNUM(TODAY()).

Do it now, right here

ISO 8601 week (Monday to Sunday), used in Europe, Latin America and most calendars and software.

Find the week of a date

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Dates of a week

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All weeks of 2026

2026 has 53 ISO weeks.

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

Step by step

  1. Put a date in A1.
  2. ISO week: =ISOWEEKNUM(A1).
  3. US week: =WEEKNUM(A1).

At a glance

FormulaWeek startsJanuary 1 is
=ISOWEEKNUM(A1)MondayWeek 1, 52 or 53
=WEEKNUM(A1)SundayAlways week 1
=WEEKNUM(A1,2)MondayAlways week 1
=WEEKNUM(A1,21)Monday (ISO)Same as ISOWEEKNUM

Related questions

How do I get the year that goes with the ISO week?

Use =YEAR(A1-WEEKDAY(A1,2)+4).

Does Google Sheets have the same functions?

Yes, ISOWEEKNUM and WEEKNUM.

Which one should I use?

ISO for Europe, Latin America and most business planning; WEEKNUM if your US team counts from Sunday.

More questions: what week is it?

Open the full what week is it? →

Updated November 14, 2026.