Is it possible to sum a value if the substraction of two value on the same row equals something?

Question

I'm trying to build a sheet where I can see how much I have to pay each month.

Let's say I have the following table

Current installment (CI)	Total installments (TI)	Installment amount (IA)
1	3	$100
1	1	$200
2	3	$150
1	3	$75
2	4	$150
1	1	$50

So, the first month would be if TI-CI >= 1, then I will sum that value. For the following month I would do the same but TI-CI >= 2

And the result would be something like this

-	-
1st month debt	$475 (the result of 100+150+75+100)
2nd month debt	$325 (the result of 100+75+150)
3rd month debt	$100

Is this possible at all?

Answer 1

try:

=IFNA(SUM(FILTER(C$2:C, (B$2:B-A$2:A)>=ROW(A1))))

and drag down