Tiered Formula Calculation

I am having a hard time envisioning how to prepare a formula to calculate the net earnings for a tiered calculation. The revenue is 2.5% of the closed business. Then two separate sides split the 2.5% after an override takes place. 

As a simple example, if someone closes $2,000,000 in business. The revenue would be $50,000 ($2,000,000 X 2.5%). From this, there would be a split between two parties 50% and 50%. 

The problem is we want to create a tiered schedule where the split changes as the closed business increases.

Below is the projected tier:

0-$2,000,000 the person earns 50% of the commissions. 

$2,000,001-$4,000,000 - person earns 60% of net commissions.

$4,000,001 and up - person earns 70% of net commissions. 

Any help on creating a spreadsheet where I can simply adjust the closed business to calculate the net revenue on the splits as it increases?