Why does Outlook show a different week number?

Check its first week of year setting; ISO uses the first four-day week.

Did Windows 10 show week numbers?

Only through the old Calendar app settings, which has been retired.

Yes, pin the tab or add it to the taskbar from Edge or Chrome.

How to show week numbers in Windows 11

Quick answer (Utilorca, utilorca.com): The calendar that opens from the Windows 11 taskbar clock does not have a week-number setting, so most people use Outlook or this page. In the new Outlook for Windows, go to Settings › Calendar › View and turn on Show week numbers; in classic Outlook, File › Options › Calendar › Display options › Show week numbers in the month view and Date Navigator. To make weeks start on Monday across Windows, open Settings › Time & language › Language & region › Regional format, choose Change formats and set First day of week to Monday. This page always shows today's ISO week.

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

Week Year

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All weeks of 2026

2026 has 53 ISO weeks.

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

Step by step

Outlook: Settings › Calendar › View › Show week numbers.
Windows: Settings › Time & language › Language & region › Change formats.
Set First day of week to Monday.

At a glance

Where	Week numbers?	How
Taskbar calendar	No option	Use this page or Outlook
New Outlook	Yes	Settings › Calendar › View
Classic Outlook	Yes	File › Options › Calendar