Looks to me like based on the number of contracts signed, you're assigning one of four numbers:
0 - 1,399,999 is 0
1,400,000 to 2,399,999 is 0.007
2,400,000 to 3,299,999 is 0.010
3,300,000 and higher is 0.013
If that is correct, give this a try:
IF({Count (Purchase Contracts Signed)} <= 1399999,
0,
IF({Count (Purchase Contracts Signed)} <= 2399999,
0.007,
IF({Count (Purchase Contracts Signed)} <= 24000000,
0.01,
0.013
)
)
)