Car Loan Calculator
How Auto Loan Interest Works
Car loan interest isn't a fixed fee spread evenly over the loan. It's charged each month on what you still owe, so it's heaviest at the start and shrinks as you pay the loan down. Knowing how that works shows you where the real savings are.
Short answer: each month the lender charges your APR divided by 12 on the remaining balance. The rest of your payment reduces the balance. A lower APR, a shorter loan and extra payments toward principal all cut the total interest you pay.
How each payment is split
Most car loans are simple-interest, amortized loans. Your monthly payment stays the same, but the split between interest and principal changes every month. Take a $30,000 loan at 6.5% APR for 60 months. The payment is $586.98.
In the first month, the interest is $30,000 × 6.5% ÷ 12 = $162.50. The other $424.48 of the payment goes to the balance, which drops to $29,575.52. Next month the interest is charged on that slightly smaller balance, so a little more of the payment goes to principal, and so on until the loan is paid off.
monthly interest = remaining balance × APR ÷ 12
Why the first years cost the most
Here is the same loan, year by year:
| Year | Interest paid | Principal paid | Balance at year end |
|---|---|---|---|
| Year 1 | $1,795 | $5,248 | $24,752 |
| Year 2 | $1,444 | $5,600 | $19,152 |
| Year 3 | $1,069 | $5,975 | $13,177 |
| Year 4 | $669 | $6,375 | $6,802 |
| Year 5 | $242 | $6,802 | $0 |
Over the whole loan you pay $5,219 in interest. $1,795 of it is in the first year and only $242 in the last. That's why paying off a loan early saves a lot in year one and very little in the final year, and why refinancing late in a loan rarely helps.
What a higher APR costs
APR has a bigger effect than most people expect. The same $30,000 loan at 9% APR has a payment of $622.75, only $35.77 more a month, but the total interest rises to $7,365: $2,146 more over five years. Small differences in rate are worth shopping for. Getting a pre-approval from a bank or credit union before you visit the dealer gives you a rate to compare against the dealer's offer.
Paying extra toward principal
Because interest is charged on the balance, every extra dollar of principal you pay stops earning interest for the rest of the loan. Adding $100 a month to the payment above pays the loan off in 50 months instead of 60, and cuts the total interest to $4,323, a saving of $896.
Before you pay extra, check two things with your lender:
- How extra payments are applied. Ask for them to go to principal. Some lenders otherwise treat extra money as an early payment of next month's bill, which doesn't save interest.
- Prepayment penalties and precomputed interest. Most car loans have neither, but some do. With precomputed interest, the interest is set when the loan is made, so paying early saves less. Your contract will say.
Three ways to pay less interest
- Lower the rate. Improve your credit before you buy, compare lenders, and use a pre-approval to negotiate.
- Shorten the loan. A shorter term has a higher payment but much less interest. See whether a 72- or 84-month loan is a bad idea.
- Borrow less. A bigger down payment, or paying tax and fees in cash instead of financing them, means less balance for interest to build on. See how much to put down.
Try it with your own numbers: Auto loan calculator →
Figures in this guide come from the same code that runs the calculators. They're estimates, not financial advice; your lender's numbers are final. How the calculators work.
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- Is a 72- or 84-Month Car Loan a Bad Idea?What a longer car loan saves you each month, what it costs in total interest, and the negative-equity risk that comes with it.
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- How Much Car Can I Afford?The 20/4/10 rule explained with real numbers, plus how loan length and other car costs change what your income supports.
- When Does Refinancing a Car Loan Make Sense?How to tell whether a refinance saves money: rate drop, fees, break-even month, and the trap of stretching the loan.