Firstly I don't believe that formula can return FALSE, whatever the inputs.
If you are convinced that it does, firstly copy the formula from your
formula bar and paste it here into the group; don't try to retype it.
Also tell us what is in each of the cells which are inputs to that formula,
in this case L8, E8, and M8.

Secondly you have unnecessary parentheses.
=IF(L8="50%",(E8-M8),IF(L8="0%",(H8-M8),0)) can be simplified to
=IF(L8="50%",E8-M8,IF(L8="0%",H8-M8,0))

Thirdly, are you sure that you want text strings for your percentage tests?
If you want numbers, ditch the quote marks.
=IF(L8=50%,E8-M8,IF(L8=0%,H8-M8,0))

Fourthly, the cells you refer to in your formula are not the cells you refer
to in your text, so sort out which row you are using.

Fifthly, I assume that when you talk about "substration" and "substraction"
you mean "subtraction"? If so, your method is correct, in that E8-M8 will
subtract the value in M8 from the value in E8.

Sixthly, you say no other options are available other than 50% or 0%. If
so, you may wish to flag an error if invalid inputs are given either in your
formula
=IF(L8=50%,E8-M8,IF(L8=0%,H8-M8,"Invalid input - only 50% or 0% permitted"))
or by the use of data validation in your L8 input cell.
--
David Biddulph

"Carolina" wrote in message
...
I have data in E7 and in H7. Depending on which data they want to go with I
need a formula to make a substration. If they select in L8 that they want
the
50% program then in another cell I need the result of E7-M7. If they
select
in L8 that they want the 0% program then in another cell I need the result
of
H7-M7. No other options available.

My attempt was the following but I got FALSE....I need the differences:
=IF(L8="50%",(E8-M8),IF(L8="0%",(H8-M8),0))

Can you help???

Thanks.
Carolina