I need a formula to calculate the payout based on cumulative sales once a breakpoint amount is exceeded.

[JCharacter]

Example:
[TABLE="width: 337"]
<colgroup><col><col><col><col></colgroup><tbody>[TR]
[TD][/TD]
[TD]A[/TD]
[TD]B[/TD]
[TD]

C​

[/TD]
[/TR]
[TR]
[TD]1[/TD]
[TD]Fee
[/TD]
[TD]Cumulative Fee [/TD]
[TD]

Payout​

[/TD]
[/TR]
[TR]
[TD]2[/TD]
[TD] $ 800,000[/TD]
[TD] $ 800,000[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]3[/TD]
[TD] $ 400,000[/TD]
[TD] $ 1,200,000[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]4[/TD]
[TD] $ 900,000[/TD]
[TD] $ 2,100,000[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]5[/TD]
[TD] $ 700,000[/TD]
[TD] $ 2,800,000[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]6[/TD]
[TD] $ 600,000[/TD]
[TD] $ 3,400,000[/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD="colspan: 3"]Payout Formula[/TD]
[/TR]
[TR]
[TD][/TD]
[TD="colspan: 2"]Cumulative Fee[/TD]
[TD]Payout[/TD]
[/TR]
[TR]
[TD][/TD]
[TD] $ 0 [/TD]
[TD] $ 1,000,000[/TD]
[TD="align: right"]50%[/TD]
[/TR]
[TR]
[TD][/TD]
[TD] $ 1,000,001[/TD]
[TD] $ 2,000,000[/TD]
[TD="align: right"]60%[/TD]
[/TR]
[TR]
[TD][/TD]
[TD] $ 2,000,001[/TD]
[TD] $ 3,000,000[/TD]
[TD="align: right"]70%[/TD]
[/TR]
[TR]
[TD][/TD]
[TD] $ 3,000,000[/TD]
[TD][/TD]
[TD="align: right"]80%[/TD]
[/TR]
</tbody>[/TABLE]

Where the payout for cell A3 ($400,000) is $220,000 (200,000@.50 and $200,000 @.60)