I am using my Google Spreadsheet to keep tabs of my incomming and outgoing money. I've made a row with ~19 cells in it, in those 19 cells I have the monthly what comes in and what goes out. At the end I add this all up and then subtract a different cell that adds up random costs.

But my problem here is that the calculation `=SUM(C4:C17)` counts everything, even the money that has not come in or that was spend. But I don't want to fiddle around with that calculation all the time.

Is it possible to make every cell in row C red and when it’s red it does not count (so it will be ignored) but if I make the cell green it gets added in the grand total?

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You can use the `SUMIF()` function with some additional (let it be D) column with 0 and 1 values. 1 will mean that the number on the same row counts, and 0 that it does not (the same what you call red).
Next use `SUMIF(D4:D17, 1, C4:C17)``(SUMIF(range,criteria,sum_range))` to sum only the numbers in the row which have 1 in the additional column D.