Formula that will calculate sum in excel?

Without seeing your precise spreadsheet and knowing what types of figures you already have and what cells they are in, it is impossible to give you the precise formula. There are also various ways you could do it, but the function you would be most likely to use is the Sum function. So if you already have individual incomes and just want to total them, then in the cell where you want the total type in:

=Sum(

and then select the cells that you want added using the mouse and then press enter.

If your figures were in cells B1, B2, B3, B4, B5, B6 and B7 and your formula was in B8, then the formula would be:

=Sum(B1:B7)

That is telling Excel to add all the values in the cells from B1 to B7.