Not being an experienced user of Excel, I have a problem thats driving me crazy. I have built a budget sheet which shows total spending for the month. The next cell shows the expected spending for the month. The third cell will show the difference between the other two. The problem is that the expected spending might be a negative number and the total spending shows a positive number but I can't get the difference cell to show the correct amount.

ie. a3 $22.00 a4 -$20.00 a5 $42.00

Formula is =a3-a4. Can someone help.