DateDif equation in an IF formula using roundup

Hello-

Does anyone know if I can "tweak" a formula to round a date up when it is inside of a longer equation?

I've attached a sample.

I can get the formula to work... with one exception, I cannot leave the cell blank or it will populate with one.

I tried to use plain datedif however since the end date is the end of the month, the formula thinks that the number of months is 1 month shorter than it really is. I had to add +1 after each part of the formula. Thus resulting in an accurate answer.

The problem is, if the dates are blank, the answer will be one.

I cannot use conditional formatting since there is the offchance that there will be a true 1 month answer.

Is there a way I can change the formula to only roundup the end date to the next month when calculating the formula?

Perhaps just

=DATEDIF(MAX(A2,D2),B2+1,"M")