Stop Formula After Condition is Met

So the problem I'm having is I'm trying to make a formula that is adaptive to the rest of the formula but I don't know how to stop it after the conditions are met. I've attached an example and the highlighted row is the one I'd like fixed. The conditions are if the other cells are blank then that one should be blank too. But if it is the final year in the model then it should equal a certain value. The problem I'm having is I don't know how to stop it after the conditions are met. Any help is appreciated. Thanks

Where are the "conditions" defined?

The condition is just if the next year is blank or if it's the final year in the model then it equals sales expense. The attachment is really just an example of what I'd like it to look like if it works

In B18: =IF(NUMBERVALUE(RIGHT(B14;2))=0;$B$3;IF(AND(B17=0;C15="";B15<>0);$B$4;0))

The first IF checks if the right number is 0 in the year (because its the first year) and if it's true it will grab the value from B3. If it's not true, I ask if this years asset management fees are 0, and the next year's date is empty, and this years date is NOT empty (in essence, this checks if this is the last year based on the dates) and it gives the result from B4, else it gives 0.

I get a False statement on the blank cells but that's an easy fix. Thanks for your help