Help with writing a formula to calculate based on a range of numbers

This might be a bit confusing. I am trying to make a real estate broker commission calculator. I have attached file for reference of what I'm working on.

Under the "Summit Properties" column, our brokers receive 80% commission of the sales and our brokerage receives the other 20%. Once they have paid our brokerage $10,000, their 80% commission split changes to 100%. I've figured out all the code except for how to make it so their annual commission calculates based on the first 80% then the 100% commission on top of that. Here is the formula in words that I cannot figure out how to write:

I want the first $10,000 in D20 to always calculate by D12*.03*.8, then after that $10,000, I want it to continue to calculate by D12*.03

Basically Summit brokers get an 80% commission split of the sale of the house (Home price * .03% *.8) while the other 20% goes to our brokerage. After $10k has been paid to the brokerage, the broker gets 100% commission of the "Home Price * .03%".

Cell D20 needs to take in the fact that the first $10k was made with an 80% commission split and not 100%.

Not quite there JeteMC.

D14 will always be at 80% until D18 hits $10,000 or more (results of paying brokerage the $10k annual cap). After D18 >= $10,000 then D14 changes to 100%. The problem with this is then the whole equation takes into account that the broker's annual commission will be 100% the whole time - it does not include the first $10k being made from an 80% commission. Do you know what I mean?