Use the IsBlank() worksheet function in your formula.
(This does not require VBA programming, so these types of questions
could/should be posted in the Worksheet.Functions newsgroup.)

For example, if cell A2 is blank, then cell B2 would have the formula:
=IF(ISBLANK(A2),"",YourFormulaHere)

or

=IF(ISBLANK(A2),0,YourFormulaHere), with column $B formatted not to show
values if they are 0.
--
Regards,
Bill Renaud