The same car both ways over the same months, with the buyer credited for what it is still worth. Comparing the two monthly payments tells you nothing — a lease is always lower, because you are renting the depreciation.
The real out-the-door number — including whether your state credits your trade-in against the sales tax.
Money factor, residual, and the payment — taxed by your state's actual method, since some states tax a lease's full value upfront instead of each payment.
Whether refinancing your car loan is worth it — including whether a lower payment is being bought with a longer term on a depreciating asset.
A dealer offers 0% financing or $3,000 cash back. On a $38,000 car over 60 months the two cost exactly the same at 3.70% — and above that, the 0% wins by thousands.
Co-signing a $683-a-month car loan cuts the house payment you can qualify for by $683 — dollar for dollar. And if it defaults, you owe the whole balance, not half.
One number, in writing, itemised — and the scripts that get it. Every line a dealer can add, which of them are negotiable, and what your own state's tax rules do to the total.
One number, itemised, with the taxable amount working your state's trade-in rule live rather than leaving it to you to remember: four states with a sales tax credit nothing against a trade-in, and Ohio credits it against a new vehicle only. Checks a documentation fee against the nine statutory caps this site has confirmed, and is explicit that the other 41 states are unresearched rather than uncapped. Prices the F&I office as the optional extra it is, and adds the trade-in payoff back into the amount financed — because negative equity does not disappear when you trade the car, it moves into the new loan and accrues interest.