A lower payment feels like a win — until the extra years of interest arrive, along with the months you spend owing more than the car is worth. Compare 36 to 84-month terms side by side.
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What does each loan term really cost?
Enter the deal on the table. The table compares every common term — and the equity chart shows exactly when you stop being underwater.
How it works: each term's payment comes from the amortization formula; total interest = payment × months − amount financed. The car's value follows a standard depreciation curve — roughly 20% in the first year, then about 15% a year after — so the chart flags every month the balance sits above the value. Those are the "underwater" months: selling or totaling the car then would leave you owing the difference out of pocket.
How auto loan terms change the real cost
Every extra year on a car loan buys you a smaller payment — and sells you more interest. The payment drops because the same debt is sliced into more pieces; the interest climbs because each piece carries another month of interest charges. The table above makes the trade exact: on a typical deal, stretching from 48 to 72 months saves about $186 a month but adds more than $2,000 in interest.
The formulas
monthly payment = principal × rate ÷ (1 − (1 + rate)−months) · total interest = payment × months − principal
The principal is the vehicle price minus the down payment — that is the amount actually financed. The monthly rate is the APR divided by 12. Run the payment formula once per term and the differences fall out of the same inputs, which is why the comparison table can show all five terms at once.
Worked example: $28,000 car, $1,000 down, 6.9% APR
You finance $27,000. On a 48-month term the payment is $645.30 a month — $30,974 all in, $3,974 of it interest — and the loan never sits above the car's value. On a 72-month term the payment drops to $459.03 — $33,050 all in, $6,050 of it interest — and the loan spends months 7–26 underwater, owing up to $837 more than the car is worth. The longer term saves $186.27 a month but costs $2,076 more in interest and nearly two years of owing more than the car is worth. Stretch to 84 months and interest climbs to $7,119 — $4,151 more than the 36-month term.
Where this comes in handy
The dealer's favorite question: "what monthly payment works for you?" is how terms get stretched to 72 or 84 months — the payment looks small while the interest quietly doubles. Compare the term, not just the payment.
Underwater checks: selling or trading in during the first few years of a long loan can mean writing a check for the difference. The chart shows your danger window before you sign.
Used-car math: a cheaper car at a higher used-car APR can beat a new car at a promotional rate — plug both in and compare total interest, not sticker prices.
Refinance timing: if your credit score improved since you bought, refinancing around month 6–18 can drop the rate; size the savings with the refinance break-even calculator.
Auto Loan Term Calculator — frequently asked questions
How much more interest does a 72-month car loan cost than a 60-month one?
On a $27,000 loan at 6.9% APR: the 60-month term costs $5,002 in interest; the 72-month term costs $6,050. That is $1,048 more for 12 extra months — roughly $87 of interest per added month at this rate. Enter your own numbers above to see your exact difference.
Why do long car loans go "underwater"?
Because cars lose value fastest in the first year (about 20%) while early loan payments are mostly interest, so the balance barely moves. With a small down payment and a 72 or 84-month term, the value curve drops below the balance curve and stays there for years. On the default example above, the 72-month loan is underwater from month 7 to month 26. A bigger down payment shortens or eliminates that window.
Is an 84-month car loan ever a good idea?
Rarely. On the example numbers, 84 months costs $7,119 in interest versus $2,968 on 36 months — and the car is worth roughly 30% of its original price by payoff. The only case for it is when the payment is genuinely unaffordable on a shorter term and you plan to pay extra toward principal (which the table's numbers don't assume). If you take one, check the underwater window first.
What difference does my down payment make?
Two: it shrinks the amount financed (so less interest on the same term), and it buys you a head start against depreciation. On a $28,000 car at 6.9% for 72 months, raising the down payment from $1,000 to $5,000 cuts interest from $6,050 to $5,154 and wipes out the underwater period entirely — the loan never sits above the car's value.
What happens if I roll negative equity into a new car loan?
You finance the new car plus the old loan's leftover balance — say $4,000 underwater on the trade-in gets added to a $28,000 loan, so you are paying interest on $32,000 while driving a $28,000 car. That is how the underwater cycle deepens: bigger balance, same depreciation. It is almost always cheaper to keep the old car until the balance is below its value.
Can I take a 60-month loan and pay it off like a 48-month one?
Yes — if the loan has no prepayment penalty (most auto loans don't), every extra dollar goes to principal and shortens the term. That gives you the 48-month interest bill with the 60-month payment as a safety net. See exactly how much the extra payments save with the extra loan payment calculator.