Gary is suggesting not using a macro, but using code like this

Private Sub Worksheet_Change(ByVal Target As Range)
Const WS_RANGE As String = "A1,B1"

On Error GoTo ws_exit:
Application.EnableEvents = False
If Not Intersect(Target, Me.Range(WS_RANGE)) Is Nothing Then
With Target
Me.Cells(.Row, "C").Value = Me.Cells(.Row, "A") + _
Me.Cells(.Row, "B").Value
End With
End If

ws_exit:
Application.EnableEvents = True
End Sub

'This is worksheet event code, which means that it needs to be
'placed in the appropriate worksheet code module, not a standard
'code module. To do this, right-click on the sheet tab, select
'the View Code option from the menu, and paste the code in.





--

HTH

RP
(remove nothere from the email address if mailing direct)


"fredonic" wrote in message
...
Could you be more specific, as I am still learning to program in excel.

"Gary''s Student" wrote:

Use a worksheet change event macro. It can detect two cells entered and
calculate the third, See:

http://www.mvps.org/dmcritchie/excel...m#wb_shtChange

--
Gary''s Student


"fredonic" wrote:

If I input a formula e.g. 'A1+B1=C1'; how do I tell excel to calculate
B1 if
I have A1 and C1's values or A1 if I have the other 2 values - doing
all this
using only the 3 original cells