Speed up vba loop - excel

Question

Every week in work I have a file of around 15000 customers that I need to break up into two categories based on their names. My current code works but it loops through every row taking almost 3 minutes to run. What would be the best way to improve the speed - I'm assuming there are much more efficient methods than the lengthy if statement I've used?
Option Compare Text
Private Sub CommandButton1_Click()
Dim i As Long
Application.ScreenUpdating = False
For i = 2 To Rows.Count
If Cells(i, 33).Value = "Business" Then
Cells(i, 32).Value = "B"
ElseIf Cells(i, 33).Value = "Personal" Then
Cells(i, 32).Value = "P"
ElseIf Cells(i, 12).Value = "N" Then
Cells(i, 32).Value = "B"
ElseIf Cells(i, 12).Value = "Y" Then
Cells(i, 32).Value = "P"
ElseIf Cells(i, 20).Value = "PREMIER" Then
Cells(i, 32).Value = "P"
ElseIf InStr(1, Cells(i, 4), "LTD") <> 0 Then 'Finds each word in customer name, column D, and enters it as business customer
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "LIMITED") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "MANAGE") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "BUSINESS") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "CONSULT") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "INTERNATIONAL") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "T/A") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "TECH") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "CLUB") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "OIL") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "SERVICE") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf InStr(1, Cells(i, 4), "SOLICITOR") <> 0 Then
Cells(i, 32).Value = "B"
ElseIf Cells(i, 4).Value = "UIT" Then
Cells(i, 32).Value = "B"
Else
Cells(i, 32).Value = ""
End If
Next i
Application.ScreenUpdating = True
End Sub

Answer 1

If you want to speed up the process, I'd stop using VBA, but write a formula instead.
Example: for finding if a cell equals "Business" or "N", you can use something like this:
=IF(OR(A1="Business";A2="N");"B";"P")
For finding if a cell contains "Business", you can use something like this:
=IF(FIND("Business";A1);"B";"P")
Combining all of this using the OR() worksheet function, you can get the whole thing. Obviously you'll need to drag your formula over your the entire column within your worksheet.

Answer 2

Try
Private Sub CommandButton1_Click()
Dim i As Long, r As Long
Dim vDB As Variant
Dim Ws As Worksheet
Dim rngDB As Range
Set Ws = ActiveSheet
Set rngDB = Ws.UsedRange
vDB = rngDB
r = UBound(vDB, 1)
For i = 2 To r
If vDB(i, 33) = "Business" Then
vDB(i, 32) = "B"
ElseIf vDB(i, 33) = "Personal" Then
vDB(i, 32) = "P"
ElseIf vDB(i, 12) = "N" Then
vDB(i, 32) = "B"
ElseIf vDB(i, 12) = "Y" Then
vDB(i, 32) = "P"
ElseIf vDB(i, 20) = "PREMIER" Then
vDB(i, 32) = "P"
ElseIf InStr(1, vDB(i, 4), "LTD") <> 0 Then 'Finds each word in customer name, column D, and enters it as business customer
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "LIMITED") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "MANAGE") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "BUSINESS") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "CONSULT") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "INTERNATIONAL") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "T/A") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "TECH") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "CLUB") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "OIL") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "SERVICE") <> 0 Then
vDB(i, 32) = "B"
ElseIf InStr(1, vDB(i, 4), "SOLICITOR") <> 0 Then
vDB(i, 32) = "B"
ElseIf vDB(i, 4) = "UIT" Then
vDB(i, 32) = "B"
Else
vDB(i, 32) = ""
End If
Next i
rngDB = vDB
End Sub