I am hung up on a formula. I am not getting the blank cell as a result.
Please help!

What I am looking for:
If cell BF is empty, I need a blank cell returned. If it has a numerical
value in it, I need the formula (BF4-Y4)/Y4 returned.

This is the formula that I have currently:

=IF(ISBLANK(BF),(""),((BF4-Y4)/Y4))

Any help would be greatly appreciated.