Thread: Sum data based on data in neighboring cell

I'm trying to create a spreadsheet to manage my finances. i've seen some online and I'd think they are overly complicated. My sheet works well but I'd like to automate it just a bit more. I have a column (column C)which has all my expenditures and credits. Column D has been set for data validation and the values are description of the expenditure or credit:
IE
C-------D---------------G
100----income--------Income total
-25----gas
-50----groceries
25-----income

is it possible to formulate the sum of data in column C based on the criteria in colume D? Meaning if I wanted excel to calculate the total of each cell in column C which has the reference "income" in the cell _next_ to , it and put the output in a cell in column G?

Thanks in advance!