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What the monthly payment actually includes

A car payment is only part of what a vehicle costs each month. The payment itself covers principal and interest on the amount you financed — which is the price, minus rebates and your down payment and trade-in credit, plus sales tax, title, registration and the dealer documentation fee.

Because those taxes and fees are financed, most people borrow more than the sticker price. Rolling negative equity from your old vehicle into the new loan pushes the financed amount higher still, and that is how a $32,000 car can quietly become a $38,000 loan.

On top of the payment, budget separately for insurance, fuel, registration renewal, routine maintenance and repairs. Insurance in particular can exceed the payment on many new cars.

The 20/4/10 rule

A widely used affordability guideline says: put at least 20% down, finance for no more than four years, and keep total vehicle costs under 10% of your gross monthly income.

The logic is that new cars depreciate faster than a loan amortizes. Twenty percent down protects you from being underwater the day you drive off the lot, and a four-year term keeps you from paying years of interest on an asset that is worth less every month.

• 20% down — covers the immediate depreciation hit and avoids most negative equity.
• 4-year term — usually the longest term available at the lowest rates, and long terms often carry rate penalties.
• 10% of income — for the combined cost of payment, insurance, fuel and maintenance, not the payment alone.

Why long terms are expensive

Stretching a loan from 48 to 72 months can cut $150 off the monthly payment and add more than $2,000 in interest on a typical loan. Six- and seven-year terms also keep your balance above the car’s value for years, because depreciation front-loads.

That matters the moment something goes wrong. If the car is totaled or you need to sell early while underwater, the gap comes out of your pocket unless you carry GAP insurance.

Getting a better deal

Rate shopping is the highest-return ten minutes you can spend before visiting a dealership. A credit union pre-approval also gives you something concrete for the finance office to beat.

• Get pre-approved before you negotiate, then let the dealer try to beat your rate.
• Negotiate the out-the-door price first, financing and trade-in separately.
• Check your credit score in advance — tiers change pricing sharply, often several points of APR.
• Skip payment-focused negotiation. Aim at total cost, because any payment can be hit by extending the term.
• Read the contract for prepayment penalties, GAP coverage, service contracts and any dealer add-ons you did not ask for.
• Consider a lightly used vehicle: someone else absorbs the steepest depreciation.