The number a dealer quotes is not the number you pay.

§2.1Why the “easy monthly payment” is the wrong number to negotiate

The dealership finance office is structured to anchor the conversation on monthly payment. From the seller’s perspective this is rational: a customer focused on monthly payment is much easier to up-sell on add-ons, extended warranty, gap insurance, and term-extension — each of which trades a slightly higher monthly payment for a substantially higher total cost. From the buyer’s perspective, this is the negotiation trap. The right numbers to negotiate are the out-the-door price, the APR, and the term — and to do all three independently, not bundled into one monthly figure that obscures the components.

An honest comparison: a $30,000 vehicle financed at 7 % APR over 60 months produces a $594 monthly payment and roughly $5,640 of lifetime interest. The same vehicle financed at 7 % over 84 months produces a $453 monthly payment — lower by $141 per month, an apparent improvement — but $7,996 of lifetime interest, an increase of $2,360 over the 60-month plan. The customer focused on monthly payment trades $2,360 of real money for $141 of monthly headroom they didn’t need to give up.

§2.2The five inputs that actually move the cost

Out-the-door price

The single number that contains MSRP, dealer markup, sales tax, doc fee, registration, and any add-ons the customer chooses to keep. The advertised “sale price” on a vehicle is typically lower than out-the-door by 8–14 % once everything is added. Always negotiate the out-the-door figure, not the advertised price.

APR

The cost of the financing. Substantially affected by credit score: as of early 2026, the spread between a 720+ FICO buyer and a sub-650 FICO buyer on a 60-month new-car loan is typically 6–9 percentage points. On a $25,000 amount financed, that’s a $4,000–$6,000 lifetime difference. The APR and OTD page works through the credit-tier pricing structure.

Loan term

Longer terms reduce monthly payment but increase total interest, both because each dollar is borrowed for longer and because lenders charge slightly higher APRs on longer terms. The 60-month term is the durability sweet spot for most new vehicles; 72 and 84-month terms are increasingly common but produce substantial negative-equity exposure (see §2.4 below).

Down payment

Reduces the amount financed dollar-for-dollar. Reducing amount financed reduces both monthly payment and total interest. The traditional 20 % down recommendation has eroded with longer-term lending; the working number is enough cash plus trade-in equity to keep you on the right side of the depreciation curve in years 1–2.

Trade-in equity

Trade-in value minus amount owed on the trade. Positive equity functions like additional down payment. Negative equity (you owe more than the trade is worth) gets rolled into the new loan unless paid in cash — the most common cause of long-running negative-equity cycles. The trade-in equity page covers the mechanics.

§2.3Sales tax: the line item buyers underestimate

State and local sales tax on motor vehicles ranges from 0 % (Alaska, Delaware, Montana, New Hampshire, Oregon at the state level) to over 9 % in some metropolitan areas. On a $30,000 vehicle that’s a $0 to $2,700 swing, dwarfing most negotiation outcomes. In most states, sales tax is calculated on the vehicle price minus trade-in allowance — one of the underrated benefits of trading in: a $10,000 trade-in at a 6 % sales-tax rate saves you $600 in tax even before the equity application.

Several states (Hawaii, Kentucky, Maryland, Michigan, Minnesota, North Carolina, South Carolina, Texas, Virginia, others) tax the full vehicle price without a trade-in deduction. The sales-tax-trade-in interaction is one of the most jurisdiction-sensitive aspects of car-loan math; the calculator above applies the trade-in deduction conservatively (assuming it applies; verify against your state) and the resulting tax to the financed amount.

§2.4Loan-to-value, depreciation, and the negative-equity trap

New vehicles depreciate sharply: 9–15 % of value lost in the first year, 50–55 % lost over the first 5 years on average for non-luxury segments. Long-term financing (84 months) means principal balance falls more slowly than depreciation accelerates — the classic underwater scenario. A buyer financing 100 % of OTD price on a 7-year loan typically owes more than the vehicle is worth from month 1 through approximately month 36 of the loan.

Underwater vehicles are not just an inconvenience. Trading in a vehicle with negative equity rolls that negative equity into the next loan, compounding the problem and producing chronically over-financed buyers. Total losses (theft, severe accident) on underwater vehicles produce out-of-pocket gaps the insurance settlement won’t cover unless you carry gap insurance — which the dealer F&I office will sell you, often at substantial markup. The dealer F&I page covers the products and what they actually cost.

§2.5The case for credit-union financing

Most dealer-arranged financing is brokered: the dealership shops your application to multiple lenders and adds a markup (the “dealer reserve”) to whatever rate the lender quotes back. The markup is typically 1–2.5 percentage points of APR, capped in some jurisdictions but uncapped in many others. Credit-union financing, arranged directly with the credit union, does not include this markup. For a 60-month $25,000 loan, a 1.5-percentage-point APR difference is roughly $1,000 of total interest.

The practical sequence: pre-qualify with your credit union (or another direct lender) before visiting the dealership. Bring the pre-approval letter. Use the dealer’s F&I quote only if it beats the credit union’s rate after fees. Most of the time it will not, especially for buyers with prime credit. The dealer’s incentive to compete is real but often modest.

§3.1Methodology and editorial standards

Calculations follow standard fixed-rate amortisation as taught in the AFCPE Accredited Financial Counselor curriculum and the AICPA personal-financial-planning materials. The calculator handles sales tax on the (price minus trade-in) base, which is the dominant US convention; verify against your state’s specific rules. Reviewer credentials are verifiable on the AFCPE certificant directory. Calculation discrepancies are corrected within five business days where reproducible — see the contact page. Editorial corrections are timestamped and an audit trail is retained.