Financial reporting

Hi, I have income and expenditure information from our accounts which is grouped in one matrix. At the moment the income is formatted as -ve numbers and the expenditure as +ve numbers. I want to format income as +ve numbers and expenditure as +ve numbers. If i do this, the total will just add the income and expenditure. Is there any way to create a grand total that subtracts the total income from the total expenditure in the matrix.