I got frustrated by the wall of numbers at car dealerships and realized that standard lease calculators often miss the subtle, iterative math that dealers use to bake in profit. So, I built an engine to completely reverse-engineer dealer paperwork.
The core issue isn't necessarily that dealers lie; it's that they use complex, perfectly legal math (like marking up the Money Factor or capitalizing taxes differently by state) to obscure the true cost. To prove the model works, I spent the last few months running real dealer quotes—like a Mercedes GLC 300 in Louisiana (stream tax) vs. a Lexus TX 350 in Georgia (capitalized tax)—through the engine.
In every case, it back-calculates the exact Net Capitalized Cost, separates the interest rate markup from the captive lender's buy rate, and verifies the monthly payment to the exact cent.
I’ve detailed the math and methodology in the link, and you can run your own lease numbers through the live tool.
I’d love for this community to stress-test the app, poke holes in my tax logic, or let me know if I'm missing any obscure local fee structures. Happy to answer any questions about the reverse-engineering process or the state-by-state calculations!
Hi HN, I'm the builder behind QuoteDefender.
I got frustrated by the wall of numbers at car dealerships and realized that standard lease calculators often miss the subtle, iterative math that dealers use to bake in profit. So, I built an engine to completely reverse-engineer dealer paperwork.
The core issue isn't necessarily that dealers lie; it's that they use complex, perfectly legal math (like marking up the Money Factor or capitalizing taxes differently by state) to obscure the true cost. To prove the model works, I spent the last few months running real dealer quotes—like a Mercedes GLC 300 in Louisiana (stream tax) vs. a Lexus TX 350 in Georgia (capitalized tax)—through the engine.
In every case, it back-calculates the exact Net Capitalized Cost, separates the interest rate markup from the captive lender's buy rate, and verifies the monthly payment to the exact cent.
I’ve detailed the math and methodology in the link, and you can run your own lease numbers through the live tool.
I’d love for this community to stress-test the app, poke holes in my tax logic, or let me know if I'm missing any obscure local fee structures. Happy to answer any questions about the reverse-engineering process or the state-by-state calculations!