To calculate your auto loan payment, divide your rate by 12 for the monthly rate, then apply the loan formula to the amount you borrow: payment equals loan amount times monthly rate, divided by one minus one plus the monthly rate to the power of minus the number of months. You borrow the price minus your down payment and trade-in.
What Goes Into Your Monthly Payment
Five numbers decide your monthly car payment, and changing any one of them changes the result. The car price is the starting point. Your down payment and trade-in value are subtracted from it, because you only borrow what is left. The interest rate (APR) is the price the lender charges for the loan, and the loan term is how many months you take to pay it back.
A bigger down payment shrinks the amount you borrow, so the payment falls. A lower interest rate does the same. A longer term also lowers the monthly payment, but it raises the total interest you pay over the life of the loan, so it is not free money. The cheapest car is not always the one with the lowest sticker price — a lower rate or a bigger trade-in can matter more than a small discount.
The Auto Loan Payment Formula
The standard formula lenders use is called amortisation. In plain words: monthly payment equals the loan amount multiplied by the monthly interest rate, divided by one minus one plus the monthly rate raised to the power of minus the number of months. Written with letters, where P is the amount borrowed, r is the monthly rate and n is the number of months, it is M equals P times r, divided by one minus one plus r to the power of minus n.
You do not need to work this out by hand every time. The formula matters because it shows why each input matters: the payment grows with the amount borrowed and with the rate, and it falls as the term gets longer. Use the free Auto Loan Calculator to run the same maths in seconds, with a year-by-year breakdown of interest and balance.
Worked Example: a $30,000 Car
Suppose you buy a car for $30,000, put $5,000 down and trade in your old car for $3,000. The amount you borrow is $30,000 minus $5,000 minus $3,000, which is $22,000. The lender offers 6.9 percent APR over 60 months. The monthly rate is 6.9 percent divided by 12, which is 0.575 percent, or 0.00575.
| Figure | Value |
|---|---|
| Car price | $30,000 |
| Down payment | $5,000 |
| Trade-in value | $3,000 |
| Amount borrowed | $22,000 |
| APR | 6.9% |
| Loan term | 60 months |
| Monthly payment | $434.59 |
| Total paid over 5 years | $26,075.35 |
| Total interest | $4,075.35 |
So the payment is $434.59 a month. Over five years you pay $26,075.35 in total, which means $4,075.35 of it is interest. That interest figure is the real cost of borrowing, and it is the number to watch when you compare two loan offers.
A Second Example: Shorter Loan, Higher Rate
Now take a $25,000 car with a $2,000 down payment, no trade-in, a 7.5 percent APR and a 48-month term. The amount borrowed is $23,000 and the monthly payment works out to $556.11. The payment is higher than the first example even though the car is cheaper, because the term is a year shorter and the rate is higher.
The shorter term still wins on total cost. You pay the loan off a full year sooner, and you pay interest for 48 months instead of 60. As a rule, the shortest term whose monthly payment you can comfortably afford is usually the cheapest loan overall.
Three Ways to Lower Your Payment
First, put more money down. Every extra $1,000 down cuts the amount borrowed by $1,000, and on a 60-month loan at 6.9 percent that saves about $19.75 a month and about $185 in interest. Second, improve the rate before you shop: even one percentage point less on a $22,000 loan saves roughly $10 a month. Check your credit report for errors, pay down card balances and get quotes from more than one lender, because dealers are not always the cheapest source of car finance.
Third, stretch the term — but only with your eyes open. Moving from 48 to 72 months can cut the payment by a fifth, yet it can add thousands in interest and leave you owing more than the car is worth for years. A longer term is a tool for affordability, not a discount.
Mistakes to Avoid
The most common mistake is shopping by monthly payment alone. A dealer can always hit your target payment by stretching the term, while the total cost quietly grows. Always ask for the total interest and the total amount paid, not just the monthly figure.
Two more traps: rolling the remaining balance of your old loan into the new one, which means paying interest on a car you no longer own, and forgetting the out-the-door price. Taxes, registration and dealer fees are often added after the sticker price, and they are part of what you borrow unless you pay them in cash. Work out the payment on the full out-the-door total, not the advertised price.
Frequently Asked Questions
What is the formula to calculate an auto loan payment?
The monthly payment equals the loan amount times the monthly interest rate, divided by one minus one plus the monthly rate to the power of minus the number of months. The monthly rate is the annual APR divided by 12, and the loan amount is the car price minus your down payment and trade-in value.
How much is the monthly payment on a $30,000 car?
It depends on your down payment, trade-in, rate and term. With $5,000 down, a $3,000 trade-in, a 6.9 percent APR and a 60-month term, the payment is $434.59 a month, with $4,075.35 of total interest. Change any input and the payment changes with it.
Does a bigger down payment lower my car payment?
Yes. A bigger down payment reduces the amount you borrow, which lowers both the monthly payment and the total interest. On a 60-month loan at 6.9 percent, each extra $1,000 down saves about $19.75 a month and about $185 in interest.
Is a longer auto loan term better?
A longer term lowers the monthly payment but raises the total interest, and it can leave you owing more than the car is worth. It helps affordability, but the shortest term you can comfortably afford is usually the cheapest loan overall.
Try it yourself: use our free Auto Loan Calculator to get your number in seconds — no sign-up needed.