So I apologize for not giving a thorough explanation as I am a newbie to Numbers! Here's what the whole formula actually is: (Budget Food−'Actual- January' Food)+(Budget Food−'Actual - February' Food)+(Budget Food−'Actual - March' Food)+(Budget Food−'Actual - April' Food)+(Budget Food−'Actual - May' Food)+ (IF(ISBLANK('Actual - June' Food),"",Budget Food−'Actual - June' Food) +(Budget Food−'Actual - July' Food)+(Budget Food−'Actual - August' Food)+(Budget Food−'Actual - September' Food)+(Budget Food−'Actual - October' Food)+(Budget Food−'Actual - November' Food)+(Budget Food−'Actual - December' Food)) (See Below).
So for every category in my budget, I would like to keep a running total of what the amount is in that category, be it either positive or negative. I have a row for every category and what the budget allowance is. Then I have a final column at the right that should be the only one that has a formula in it.
The formula above is in the final column and it worked well until I tried to tell Numbers to not calculate any blank cells, (I was practicing this for the month of June). In this example I left the entire formula in but I added what I thought would tell Numbers to not calculate blanks.

This is the error it keeps returning:
The operator “+” expects a number, date, or duration but found “.”

Also, how do you know if a blank cell is really empty?
Thanks so much for answering, and I hope I've explained it well enough this time!
Barb