Business computations always involve the computation of Net-Work days, and if you are using Excel, you immediately find a solution in NetworkDays function. I have myself used it extensively in my computational work. But, for reasons best known to Microsoft, they have kept this function as part of Analysis Toolpack add-in. Well, to makes obviously no difference as the addin is a part of standard Office shipment. But, when you are developing a spreadsheet to be used by many, you are not very sure whether they have the addin installed/active.

Adding a check for its presence is definitely a good idea, but depending on the Analysis ToolPack just for NetworkDays functionality is not worth it, atleast in my purview. Here is the code of a custom function that does the same for you, and in cases, can remove your dependency on ATP.

Public Function MyNetWorkDays(ByVal startDate As Date, ByVal endDate As Date, Optional ByVal holidays As range = Nothing) As Integer
	Dim diff As Integer, weeks As Integer, ed As Integer, sd As Integer, delta As Integer
	Dim swap As Boolean
	swap = False
	MyNetWorkDays = 0: delta = 0
	If endDate < startDate Then
		'swap the dates
		Dim temp As Date
		temp = endDate
		endDate = startDate
		startDate = temp
		swap = True
	End If
	diff = endDate - startDate
	ed = Weekday(endDate)
	sd = Weekday(startDate)
	weeks = diff \ 7
	If ed = sd Then
		If Not (ed = 1 Or ed = 7) Then
			delta = 1
		End If
	ElseIf ed > sd Then
		If ed = 7 Then ed = 6
		If sd = 1 Then sd = 2
		delta = ed - sd + 1
		delta = 7 - (sd - ed) - 1
	End If
	MyNetWorkDays = (weeks * 5) + delta
	' check for holidays
	If Not holidays Is Nothing Then
		For Each holiday In holidays
			wh = Weekday(holiday)
			If wh = 1 Or wh = 7 Then
				If startDate <= holiday And holiday <= endDate Then
					MyNetWorkDays = MyNetWorkDays - 1
				End If
			End If
	End If
	If swap Then
		MyNetWorkDays = 0 - MyNetWorkDays
	End If
End Function

Hope this helps!