A
B
C
D
1
Sales
Comm Rate
Diff Rate
2
$ -
0%
0%
 C2: =B2-N(B1)
3
$ 1,250,000
4%
4%
4
$ 1,500,000
5%
1%
5
$ 1,750,000
6%
1%
6
$ 2,000,000
7%
1%
7
8
Sales
Commission
9
$ 1,400,000
$ 6,000
B9: =SUMPRODUCT((A9>$A$2:$A$6) * (A9-$A$2:$A$6) * $C$2:$C$6)
10
$ 1,600,000
$ 15,000
11
$ 1,680,000
$ 19,000