How this instrument works
An auto loan is repaid the same amortizing way as a mortgage — a fixed installment sized so the balance reaches exactly zero on the loan's last month — but the term is short, typically 36 to 72 months, and the collateral loses value fast rather than holding it. The amount financed here is not the sticker price: it is the price minus any down payment and trade-in credit, plus title, registration, and dealer fees the lender agreed to roll in, plus any negative equity carried over from a previous loan the buyer traded out of early.
The monthly figure falls when either lever moves — a lower rate or a longer term — but only the rate move is free. Stretching the term from 60 to 72 or 84 months lowers the payment while adding months of interest on a balance that is falling only slowly, and it widens the stretch of the loan during which the payoff sits above the car's resale value, the situation lenders and buyers both call being underwater or upside down.
This sheet computes principal and interest only. It excludes sales tax and registration fees unless you have already folded them into the loan amount, and it has nothing to say about add-on products like gap insurance or an extended service contract that a finance office may bundle into the same monthly figure. It also has nothing to do with a lease's money factor, a different number entirely that a dealer multiplies by 2,400 to approximate an equivalent rate — this formula only prices a loan you will own the vehicle outright at the end of.
- Enter the amount you are financing under Loan amount, $ — price minus down payment and trade-in, plus any fees or negative equity rolled in.
- Set the rate your lender quoted under Annual interest rate, % — the loan's APR, not a lease's money factor.
- Enter the repayment length in months under Loan term, months; 60 is five years, 72 is six.
- Read Monthly payment for the fixed installment, then rerun the term to see how stretching it changes the number.
Worked example — a $25,000 loan at 6% over five years
Finance $25,000 at a 6% annual rate over 60 months (Loan term, months set to 60, five years). The monthly rate is r = 6 ÷ 100 ÷ 12 = 0.005, and (1.005)^60 works out to about 1.34885. Multiplying gives PMT = 25000 × 0.005 × 1.34885 ⁄ 0.34885 = $483.32, the figure Monthly payment shows for these exact inputs.
Across the full 60 payments that comes to $28,999.20 handed to the lender, of which $3,999.20 is interest and the rest retires the original $25,000. Change nothing but Loan term, months to 72 and the payment drops to $414.32, a friendlier number on paper, but total interest climbs to $4,831.20 — over $800 more, the reliable trade-off of buying a lower payment with a longer term.
Questions
Why does a longer loan term lower the payment but cost more overall?
A longer term spreads the same principal over more installments, so each one is smaller, but interest keeps accruing every month the balance survives. Stretching the golden example from 60 to 72 months drops the payment from $483.32 to $414.32, yet total interest rises from $3,999.20 to $4,831.20 — over $800 more for a smaller monthly number.
What's the difference between the rate I'm quoted and the dealer's buy rate?
The buy rate is the rate a bank or credit union actually approves the loan at; a dealer's finance office is often permitted to mark that rate up and keep the difference as compensation, so the number on your paperwork can sit above what the lender itself offered. Comparing a pre-arranged bank or credit union rate against the dealer's quote before signing is the only way to see whether a markup happened.
Does the loan amount include tax, fees, and add-ons?
Only if you enter it that way. Loan amount, $ should equal the exact amount financed on the contract — sale price minus down payment and trade-in credit, plus any tax, title, registration, or dealer fees the lender agreed to roll into the loan, plus gap insurance or a service contract if those were financed too. Leaving any of that out understates every result below it.
What does it mean to be upside down on a car loan?
It means the loan balance is higher than the car is currently worth, which happens routinely in the first year or two because a car depreciates faster than a 60-to-72-month loan balance falls. It matters most at trade-in or after an accident: a payoff above the car's value has to be covered in cash, rolled into the next loan, or absorbed by gap insurance if a total loss is involved.
Is this the same as a lease's money factor?
No. A money factor prices a lease's rent charge and is usually quoted as a small decimal like 0.00125; multiplying it by 2,400 approximates an equivalent annual rate for comparison against a loan. This instrument prices ownership financing instead — Annual interest rate, % is the loan's APR, a different number computed a different way for a different kind of contract.
References
- Consumer Financial Protection Bureau — Auto loans resources
- Federal Reserve — Consumer Credit statistical release (G.19)
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.