Week numbers in the Calendar are wrong

I’ve added week numbers to my Calendar but they don’t seem to match with my desk calendar which I believe is correct.

How can this be and how can I correct this?

Show Week Number buttonThere are several week numbering systems in use for the normal (Gregorian) calendar. The week numbering system of Outlook can be modified to match the week numbering system which is used by your country or region.

There are 2 settings that determine the week numbers that are listed in the calendar:

  • First day of week
  • First week of year

You can configure these settings by going to:

  • Outlook 2007
    Tools-> Options…-> button Calendar Options…
  • Outlook 2010 / 2013 / 2016 / 2019 / Office 365
    File-> section Options-> section Calendar

Work time options for the Calendar in Outlook 2013 allow you to define the first day and first week of the year.
Verify that your “First day of week” and “First week of year” settings are correct.


If you live in the USA, Canada, Australia, New Zealand or the UK, you most likely need to set these options to:

  • First day of week: Sunday
  • First week of year: Starts on Jan 1

If you live in Europe or want to follow the ISO standards, you most likely need to set these options to:

  • First day of week: Monday
  • First week of year: First 4-day week

Note: In the UK, as of 2004, according to the British Standards, the official first day of the week is Monday. Whether or not you should select the corresponding option depends on the level of acceptance of that standard in your sector/area.

Background info

Region - Control Panel - buttonThe initial settings for Outlook are determined by the regional settings of your Windows version.

You can change your regional settings (language, location, date notation, etc…) in the Windows Control Panel or the “Time & Language” section of the Settings App in Windows 10. You can then use the settings in Outlook to overrule the week numbering system.

This method is useful when you are using a language of Windows that doesn’t match with the language of your regional settings. In those cases the names of the days will be translated to the language that is set in your regional settings, creating a mixed language environment which often is not desired.

Your Windows version is in English but by setting your Region and Language format to Dutch, the names of the days will be displayed in Dutch as well.

By setting the language to an English format (and possibly additionally changing the formatting options in Control Panel), you can maintain a fully English working environment and use the options in Outlook to match the week numbering system of your region.

For detailed instructions about how to alter the Region and Language format in Windows see: Change language of calendar (days and months).

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