According to the calculator 101 page, LH Calculator and how to use it
The selling price is the MSRP minus trade-ins and dealer discounts, without any incentives.
Dealer is giving $500 off MSRP. My trade-in is worth $3155.
30850 - 500 - 3155 = 27195
27185/30850 * 100 = 88.1%, or put another way, 11.9% off MSRP