The real cost of a car loan — the 84-month trap and underwater equity

Because the dealer's lever is the monthly payment, not the total cost. A 72- or 84-month term lowers the monthly number into the range the buyer 'qualified' for — which clears the deal even when total interest doubles. F&I (finance and insurance) also earns more on longer terms via add-ons (warranties, GAP, theft prevention) that get rolled into the financed amount.

It's when you owe more on the loan than the vehicle is worth. A new car typically loses 20–30% of its value the first year and ~60% by year five. With a low or zero down payment on a 72- or 84-month loan, the payoff balance can sit above the vehicle's market value for most of the loan. Selling, totaling, or trading the car during that period requires writing a check — or rolling the gap into a new loan.

On a typical new-car loan with 5–10% down at current rates, the crossover usually happens around month 36–42. On an 84-month loan with no money down, it can take 50+ months — meaning the buyer is underwater for more than half the loan. KBB and Edmunds publish depreciation curves you can sanity-check against your specific make and model.

Used auto APRs typically run 1.5–3.5 percentage points above comparable new-car APRs at the same credit tier, per Federal Reserve G.19 data. The gap reflects collateral risk (older vehicles depreciate faster from a lower base) and shorter eligible terms. A used loan often pencils better overall because the vehicle has already absorbed the steepest depreciation.

When the new APR is at least 1.5–2 percentage points below the current APR, the remaining term is at least 24 months, and no significant prepayment penalty applies. The break-even on auto refis is usually fast because closing costs are low. The trap is extending the term to lower the monthly — that resets the underwater clock and adds total interest.

Often the rebate wins. The 0% offer is funded by foregoing the cash rebate, so a $3,000 rebate financed at a market rate (e.g. 7%) can produce lower total cost than 0% APR over the same term — depending on loan size and term length. Always run both deals: total cost = (price − rebate) × amortized interest at market APR vs price × 0% APR.

Often yes if you're putting little down and financing a vehicle that depreciates fast. GAP covers the gap between insurance payout and loan payoff if the car is totaled or stolen. The mistake is buying it through the dealer at 2–3× the price your auto insurer would charge — ask your insurer first.

Over a 3-year hold, leasing usually costs less in cash outlay but builds zero equity — you hand the car back. Over a 6-year hold, buying typically wins on total cost of ownership because depreciation is concentrated in years 1–3 and the buyer captures the residual value. The decision is really about how long you'll keep the car and whether you value the lower monthly payment.

Lease payment ≈ (cap cost − residual value + finance charge) ÷ term. The residual is what the leasing company believes the car will be worth at lease end. Higher residuals (luxury models, trucks) produce lower monthly payments because there's less depreciation to amortize. A residual that's higher than the realistic resale value is a hidden subsidy from the manufacturer.

Most lenders will, but it's a wealth-destroyer. You're now financing a depreciating asset PLUS the old underwater balance, often at a higher LTV than the lender's standard limit, which pushes the new loan deeper underwater from day one. CFPB has flagged rolled-negative-equity loans as a leading driver of repossession risk.

The underwater-equity trap above isn't a fringe scenario — the New York Fed counted $1.71 trillion auto loans outstanding nationally in Q2 2026, up $28 billion for the quarter and a new record. Experian's Q1 2026 State of the Automotive Finance Market report found 35.55% of auto loans for new vehicles now run longer than six years (up from 30.83% a year earlier), with the average new-vehicle loan financing $43,925 over 69.48 months — exactly the term length where this page's underwater-crossover math (month 50+ with no money down) applies to a growing share of buyers.