Returns n-th workday in given month(skipping weekends and us holidays).

Get-WorkDay.ps1

function Get-WorkDay {
	param(
		[Parameter(Mandatory = $true)]
		[int]$Day,
		[Parameter(Mandatory = $false)]
		[ValidateRange(1, 31)]
		[int]$Month = (Get-Date).Month,
		[Parameter(Mandatory = $false)]
		[int]$Year = (Get-Date).Year,
		[Parameter(Mandatory = $false, DontShow)]
		[int]$Index = 1
	)

	begin {
		
		$USHolidays = @(
			"01/01",	# New Year's Day
			"01/20",	# Martin Luther King Jr. Day
			"02/17",	# Presidents' Day
			"05/25",	# Memorial Day
			"06/03",	# Independence Day observed
			"06/04",	# Independence Day
			"09/07",	# Labor Day
			"10/12",	# Columbus Day
			"11/11",	# Veterans Day
			"11/26",	# Thanksgiving Day
			"12/25"		# Christmas Day
		)

		$holidays = @($USHolidays | 
			ForEach-Object { [DateTime]::ParseExact("$_/$($Year)", 'MM/dd/yyyy', [System.Globalization.CultureInfo]::InvariantCulture) } |
			Where-Object { $_.Month -eq $Month })
	}
	process {
		# Handle month owerflow
		if ($Index -gt [DateTime]::DaysInMonth($Year, $Month)) {
			if ($Month -eq 12) {
				$Month = 1
				$Year++
			}
			else {
				$Month++
			}
			$Day = $Day - $Index + 1
			$Index = 1
		}

		$date = Get-Date -Year $Year -Month $Month -Day $Index

		if ($date.DayOfWeek -eq 'Saturday') {
			return Get-WorkDay -Day ($Day + 2) -Year $Year -Month $Month -Index ($Index + 2)
		}
		elseif ($date.DayOfWeek -eq 'Sunday') {
			return Get-WorkDay -Day (++$Day) -Year $Year -Month $Month -Index (++$Index)
		}
		elseif ($holidays.Length -gt 0 -and ($holidays | Where-Object { $_.Day -eq $date.Day }).Length -gt 0) {
			return Get-WorkDay -Day (++$Day) -Year $Year -Month $Month -Index (++$Index)
		}
		elseif ($Index -lt $Day) {
			return Get-WorkDay -Day $Day -Year $Year -Month $Month -Index (++$Index)
		}
		else {
			$date
		}
	}	
}