🚗 Auto Loan Calculator
By ToolNimba Finance Team · Reviewed by ToolNimba Editorial Review, personal finance content · Updated 2026-06-19
This calculator gives an estimate only. Your real car payment depends on the exact APR you qualify for, dealer and registration fees, gap insurance or extended warranties rolled into the loan, and how your state taxes the purchase (some tax the price before a trade-in credit, some after). The result is not financial advice. Confirm the final figures in your loan agreement and speak to a qualified adviser before borrowing.
This auto loan calculator works out the monthly payment on a car loan, plus the total interest and total cost over the term. Enter the vehicle price, your down payment and trade-in value, the sales tax rate, the APR and the loan term in months. It subtracts your cash and trade-in, adds the sales tax, then applies the standard amortization formula so you can see what the car will really cost before you sign at the dealership.
What is the Auto Loan Calculator?
An auto loan is an amortizing loan: you borrow a fixed amount and repay it in equal monthly payments that each cover the interest due that month plus a slice of the principal. The amount you actually finance is not the sticker price. It is the price plus sales tax, minus your down payment and minus any trade-in credit. Lowering that financed amount, by putting more cash down or trading in a vehicle, is the single most direct way to shrink both your monthly payment and the total interest.
The monthly payment is found with the reducing-balance formula M = A x r x (1 + r)^n / ((1 + r)^n - 1), where A is the amount financed, r is the monthly rate (the APR divided by 12 and by 100) and n is the term in months. Because interest is charged only on the balance you still owe, the split inside each payment changes over time: early payments are mostly interest, and later ones are mostly principal. This is why a longer term feels cheaper month to month but costs much more in total interest.
APR and term are the two levers that move the cost most. A higher APR raises every payment, and even one or two percentage points adds up to hundreds or thousands of dollars over a five or six year loan. Stretching the term from 48 to 72 months drops the monthly figure but keeps you in debt, and often underwater (owing more than the car is worth), for longer. Sales tax treatment also matters: many states tax the price after subtracting the trade-in, which lowers the tax, while others tax the full price. This tool applies tax to the vehicle price, so adjust the rate if your state taxes the post trade-in amount.
When to use it
- Working out the monthly payment on a new or used car before you visit the dealer.
- Comparing a 48, 60 and 72 month term to see how much extra interest a longer loan costs.
- Checking how a bigger down payment or a trade-in changes your payment and total cost.
- Sanity-checking a dealer financing offer against your own bank or credit union quote.
How to use the Auto Loan Calculator
- Enter the vehicle price (the agreed purchase price before tax).
- Enter your down payment and the value of any trade-in.
- Enter your sales tax rate and the APR your lender is offering.
- Enter the loan term in months, then read off the monthly payment, total interest and total cost.
Formula & method
Worked examples
A $30,000 vehicle, $5,000 down, no trade-in, 7% sales tax, 6% APR, 60 month term.
- Sales tax = 30,000 x 7 / 100 = $2,100
- Amount financed = 30,000 + 2,100 - 5,000 - 0 = $27,100
- Monthly rate r = 6 / 12 / 100 = 0.005
- (1 + r)^n = 1.005^60 = 1.348850
- Payment = 27,100 x 0.005 x 1.348850 / (1.348850 - 1) = $523.92
- Total cost = 523.92 x 60 = $31,435.14
- Total interest = 31,435.14 - 27,100 = $4,335.14
Result: Payment about $523.92/mo, total interest about $4,335.14, total cost about $31,435.14
A $25,000 vehicle, $2,000 down, $3,000 trade-in, 8% sales tax, 5.5% APR, 48 month term.
- Sales tax = 25,000 x 8 / 100 = $2,000
- Amount financed = 25,000 + 2,000 - 2,000 - 3,000 = $22,000
- Monthly rate r = 5.5 / 12 / 100 = 0.0045833
- (1 + r)^n = 1.0045833^48 = 1.245451
- Payment = 22,000 x 0.0045833 x 1.245451 / (1.245451 - 1) = $511.64
- Total cost = 511.64 x 48 = $24,558.84
- Total interest = 24,558.84 - 22,000 = $2,558.84
Result: Payment about $511.64/mo, total interest about $2,558.84, total cost about $24,558.84
How the loan term changes a $25,000 amount financed at 6% APR
| Term | Monthly payment | Total interest | Total cost |
|---|---|---|---|
| 36 months | $760.55 | $2,379.74 | $27,379.74 |
| 48 months | $587.13 | $3,182.03 | $28,182.03 |
| 60 months | $483.32 | $3,999.20 | $28,999.20 |
| 72 months | $414.32 | $4,831.20 | $29,831.20 |
Common mistakes to avoid
- Choosing a long term just to lower the payment. Stretching from 48 to 72 months on a $25,000 loan at 6% drops the payment by about $173 but adds roughly $1,650 in total interest, and keeps you owing the balance for two extra years.
- Forgetting tax and fees in the financed amount. The amount you borrow includes sales tax (and often dealer, title and registration fees), not just the sticker price. Leaving them out understates both the payment and the total cost.
- Comparing loans by monthly payment instead of APR. A dealer can lower the monthly payment by lengthening the term while charging a higher rate. Compare the APR and the total interest, not just the payment, to see which loan is actually cheaper.
- Assuming the trade-in lowers your taxable amount. Some states tax the price after subtracting the trade-in, others tax the full price. This tool taxes the vehicle price, so adjust the tax rate if your state gives a trade-in tax credit.
Glossary
- Amount financed
- The sum you actually borrow: the vehicle price plus sales tax, minus your down payment and trade-in.
- APR
- Annual Percentage Rate, the yearly cost of the loan including interest, used to derive the monthly rate.
- Down payment
- The cash you pay upfront, which reduces the amount you need to finance.
- Trade-in value
- The credit a dealer gives you for your old vehicle, applied against the new purchase.
- Amortization
- Repaying a loan in equal installments that each cover interest plus a portion of principal until the balance reaches zero.
- Underwater
- Owing more on the loan than the car is currently worth, common early in a long term loan.
Frequently asked questions
How is my monthly car payment calculated?
The calculator first works out the amount financed (price plus sales tax, minus down payment and trade-in), then applies the amortization formula M = A x r x (1 + r)^n / ((1 + r)^n - 1), where r is the APR divided by 12 and 100, and n is the term in months. Enter your figures and it updates instantly.
Does a bigger down payment lower my payment?
Yes. A larger down payment reduces the amount you finance, which lowers both the monthly payment and the total interest you pay. It also reduces the risk of being underwater, owing more than the car is worth, in the early part of the loan.
Is it better to take a longer loan term?
A longer term lowers the monthly payment but increases total interest, because you owe the balance for longer. On a $25,000 loan at 6%, going from 48 to 72 months saves about $173 a month but adds roughly $1,650 in interest. Pick the shortest term you can comfortably afford.
How does APR affect the cost?
APR is the yearly interest rate on the loan. A higher APR raises every payment and the total cost. Even one or two percentage points can add hundreds or thousands of dollars over a five or six year loan, so shopping rates with several lenders is worth the effort.
Is sales tax charged before or after my trade-in?
Sales tax rules vary by state. Many states tax the price after subtracting the trade-in (which lowers the tax), while others tax the full price. This calculator applies tax to the vehicle price, so if your state gives a trade-in tax credit, lower the tax rate to approximate it.
Does the total cost include my down payment?
No. The total cost shown is the sum of all your monthly payments on the amount financed, which already excludes your down payment and trade-in. Add your down payment back if you want the total out of pocket cost of owning the car.
Sources
- Auto loans: How to get the best deal , U.S. Consumer Financial Protection Bureau
- Amortization , Investopedia