Almost all of this could be done using formulas but since you asked specifically for a macro I will do it that way. I would like to add that there are already thousands of free templates out there which are already set up and look really nice which you could use. I personally would use one of them.
Sub Calculate_Money()
Dim rPaycheck As Range
Dim rRemaining As Range
Dim rTotal As Range
Dim rBills As Range
Set rPaycheck = Range("C1")
Set rRemaining = Range("C13")
Set rTotal = Range("C16")
Set rBills = Range("C4:C12")
rRemaining = rPaycheck - Application.WorksheetFunction.Sum(rBills)
rTotal = rTotal + rRemaining
End Sub
Note: Having the merged cells like you have complicates things. Merged cells and macros don't work well together. More reason to actually use formula.
Bookmarks