Macro not calculating correctly
 

Hi,
I have this code below for every month(24 total) where the same variables
are used...every sub calls the other one. When I go through the steps one by
one via the "F8" button it calculates correctly but when I run it or press
"F5" incorrect values are calculated?
Any help ?

Thanks alot,
Ozgur

For i = 4 To 500
If Range("A" & i) = "" Then
Exit For
Else
TMC_BEG_INV_QTY = Cells(i, 3).Value
TMC_BEG_INV_AMT = Cells(i, 4).Value
TMC_PURCHASE_QTY = Cells(i, 5).Value
TMC_PURCHASE_AMT = Cells(i, 6).Value
TMC_USAGE_QTY = Cells(i, 8).Value
If (TMC_BEG_INV_QTY + TMC_PURCHASE_QTY) = 0 Then
TMC_USAGE_AMT = 0
TMC_USAGE_MAC = 0
Cells(i, 9) = TMC_USAGE_AMT
Cells(i, 7) = TMC_USAGE_MAC
Else
TMC_USAGE_AMT = (TMC_BEG_INV_AMT + TMC_PURCHASE_AMT) /
(TMC_BEG_INV_QTY + TMC_PURCHASE_QTY) * TMC_USAGE_QTY
Cells(i, 9) = TMC_USAGE_AMT
TMC_USAGE_MAC = (TMC_BEG_INV_AMT + TMC_PURCHASE_AMT) /
(TMC_BEG_INV_QTY + TMC_PURCHASE_QTY)
Cells(i, 7) = TMC_USAGE_MAC
End If
End If
Next