Finding the Last Friday (or any weekday) of the Month in PowerShell

If there are less than 7 days left in the month, then it’s the last weekday of this type in this month.

function Is-LastWeekDayOfMonth([DateTime] $d) {
    return [DateTime]::DaysInMonth($d.Year, $d.Month) - $d.Day -lt 7
}

Similarly, finding the last specific weekday of the month involves finding the last weekday, and the difference between that weekday and the target weekday:

function Get-LastFridayOfMonth([DateTime] $d) {
    $lastDay = new-object DateTime($d.Year, $d.Month, [DateTime]::DaysInMonth($d.Year, $d.Month))
    $diff = ([int] [DayOfWeek]::Friday) - ([int]
    $lastDay.DayOfWeek)
    if ($diff -ge 0) {
        return $lastDay.AddDays(- (7-$diff))
    }
    else
    {
        return $lastDay.AddDays($diff)
    }
}

Chinh Do

I occasionally blog about programming (.NET, Node.js, Java, PowerShell, React, Angular, JavaScript, etc), gadgets, etc. Follow me on Twitter for tips on those same topics. You can also find me on GitHub. See About for more info.

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View Comments

Martijn says:

August 30, 2016 at 8:50 am

Hi Chinh Do,
I stumbled upon your script today.
I was looking for something like this.
There is just one minor thing about your script.
In your If statement, you should use -gt in stead of -ge to return the correct value.

Much appreciated!
Martijn