Data validation won't work here - it only checks user entries. You can
use a worksheet event macro:

Put this in the worksheet code module (right-click the worksheet tab and
choose View Code):

Private Sub Worksheet_Calculate()
If Me.Range("A3").Value 5000 Then _
MsgBox "A3's too high - do something!"
End Sub



Or, you could attack the problem at its source. If A1 and A2 are both
manually entered, you could use Validation on A1 and A2. Select them
both and choose Data/Validation:

Allow: Custom
Formula: =($A$1*$A$2)<5000


In article ,
Rick wrote:

I want to have data validation on a cell containing a formula. Is it
possible to have validation on the results of a formula and how do you do it?
Here is what I'm doing:

A1 (QTY) A2 (UNIT PRICE) A3 (EXTENDED PRICE)

A3 HAS THIS FORMULA =A1*A2

I want to have any value exceeding $5000 in A3 cause a data validation error
alert to appear with a message instructing what to do.