Calculate Calendar Week (Part 1)

by Feb 9, 2022

Calculating the week of day isn’t trivial and can be different for different cultures. Here is a generic way to calculate the week number for any date:

# calculate day of week
# adjust calendar specs to your culture

$Date = [DateTime]'2021-12-31'
$CalendarWeekRule = [System.Globalization.CalendarWeekRule]::FirstDay 
$FirstDayOfWeek   = [System.DayOfWeek]::Monday

$week = [System.Globalization.DateTimeFormatInfo]::CurrentInfo.Calendar.GetWeekOfYear( $date, $calendarWeekRule, $firstDayOfWeek )

"$date = week $week" 

Just make sure you adjust the calendar week rule and the first day of week to your culture.

The previous example uses the current culture calendar. If you’d like to also control the culture, try using this approach:

$Date = [DateTime]'2022-12-31'
$CultureName = 'de-de'
$CalendarWeekRule = [System.Globalization.CalendarWeekRule]::FirstDay 
$FirstDayOfWeek   = [System.DayOfWeek]::Monday

$culture = [System.Globalization.CultureInfo]::GetCultureInfo($CultureName)
$week = $culture.Calendar.GetWeekOfYear($Date, $CalendarWeekRule, $FirstDayOfWeek)

"$Date = week $week"

Here, you can use $CultureName to define the culture name for the calendar to use.

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