Variable Rent Calculation

Hi,

I am trying to create a variable rent with the following specifics.

Annual Breakpoint is $12,000

Group Breakpoint is $1,000 monthly

5% is rate

First month volume is $1,500

Based on the above, I would want the system to calculate $25 of variable rent (1500 - 1000) * .05 = $25

Can someone provide the calculation method, partial year method, calculation frequencies, etc. needed in order to have the system perform the above.

Thanks in advance.