First week of year: registry value firstwoyUserHKCU\software\policies\microsoft\office\16.0\outlook\options\calendar

Policy ID: L_Firstweekofyear
Scope: User Configuration
Supported on: At least Windows Server 2008 R2 or Windows 7
Source: Microsoft 365 Apps / Office Administrative Templates (version 5568.1000)
Category: Microsoft Outlook 2016 › Outlook Options › Preferences › Calendar Options

Registry

firstwoy

REG_DWORDUser

HKCU\software\policies\microsoft\office\16.0\outlook\options\calendar Current key

Enabled value: Depends on the option value
Element: Choose the first week of the year:

Options
Item	Stored value
Starts on Jan. 1	0
First full week	2
First four-day week	1

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\outlook\options\calendar]

; Options (use only one)
; Starts on Jan. 1
"firstwoy"=dword:00000000
; First full week
"firstwoy"=dword:00000002
; First four-day week
"firstwoy"=dword:00000001

CMD

:: Options (use only one)

:: Starts on Jan. 1
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\options\calendar" /v "firstwoy" /t REG_DWORD /d 0 /f
:: First full week
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\options\calendar" /v "firstwoy" /t REG_DWORD /d 2 /f
:: First four-day week
reg add "HKCU\software\policies\microsoft\office\16.0\outlook\options\calendar" /v "firstwoy" /t REG_DWORD /d 1 /f

PowerShell

# Common: create the key
New-Item -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\options\calendar' -Force | Out-Null

# Options (use only one)
# Starts on Jan. 1
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\options\calendar' -Name 'firstwoy' -PropertyType DWord -Value 0 -Force | Out-Null
# First full week
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\options\calendar' -Name 'firstwoy' -PropertyType DWord -Value 2 -Force | Out-Null
# First four-day week
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\outlook\options\calendar' -Name 'firstwoy' -PropertyType DWord -Value 1 -Force | Out-Null