Loans & Credit
Published on September 25, 2025
A car loan uses the standard amortisation formula: Payment = P x r x (1+r)^n / ((1+r)^n - 1), where P is the amount financed after your deposit and trade-in, r is the annual rate divided by 12, and n the number of months. Financing $25,000 at 7% over 5 years costs $495.03 a month and $4,701.80 in interest.
Published by PraxisCalc, a Zeta Digilux Labs project
For most people, buying a car involves financing. A car loan can make a new vehicle affordable, but it's crucial to understand how your monthly payment is calculated so you can find a loan that fits comfortably within your budget.
Your monthly car payment is determined by a few key variables that you'll need to know before you start shopping.
The starting point is the Car Price. From this, you subtract your Down Payment (the cash you pay upfront) and the Trade-in Value of your current vehicle, if you have one. The result is the principal loan amount, the actual amount you're borrowing.
The Annual Percentage Rate (APR) is the interest rate you'll pay on the loan. This is heavily influenced by your credit score. A higher credit score will typically qualify you for a lower APR, which can save you thousands over the life of the loan.
The loan term is the length of time you have to repay the loan, typically ranging from 36 to 84 months. A longer term will result in a lower monthly payment, but you'll pay more in total interest. A shorter term means higher payments but less overall interest cost.
Experiment with different prices, down payments, and loan terms to find a monthly payment that fits your budget. Our Car Loan Calculator makes it easy.
Use the Car Loan Calculator →Before you even step into a dealership, it's a wise strategy to get pre-approved for a loan from your bank or a credit union. This gives you a clear understanding of the interest rate you qualify for and a firm budget to work with. It turns you into a "cash buyer" at the dealership, giving you more negotiating power and preventing you from being talked into a loan with unfavorable terms.
Lenders typically charge a lower interest rate on new-car loans than on used-car loans, because a new vehicle is worth more as collateral and depreciates from a known starting value. Used-car rates run higher partly to offset the harder-to-predict condition and remaining lifespan of an older vehicle, and the gap widens further for older or higher-mileage vehicles. This means a used car with a lower sticker price doesn't always produce a proportionally lower payment once the higher rate is factored in, so it's worth comparing the actual financed cost, not just the purchase price, across both options.
Because vehicles depreciate faster than a typical loan balance declines in the first year or two, it's common to owe more on the loan than the car is worth, especially with a small down payment or a long loan term. Guaranteed Asset Protection (GAP) insurance covers that gap if the car is totaled or stolen, since a standard auto insurance payout only covers the vehicle's current market value, not the remaining loan balance. GAP coverage is most worth considering when your down payment is small, your loan term is long, or you rolled negative equity from a trade-in into the new loan, all of which widen the gap between what you owe and what the car is worth.
If your credit score improves after you take out a car loan, or if market interest rates drop, refinancing can lower your monthly payment or reduce total interest over the remaining term. Refinancing is generally most worthwhile in the first half of the loan, since that's when the largest share of each payment still goes toward interest; refinancing very late in the term has less room to meaningfully improve your total cost. Before refinancing, check for any prepayment penalty on the current loan and confirm the new loan's fees don't outweigh the interest savings.
Dealer-arranged financing can sometimes offer promotional rates, but it also often includes a markup added by the dealership on top of the rate the lending bank actually approved, so the advertised rate isn't always the best available rate for your credit profile. Getting pre-approved through your own bank or credit union first gives you a real baseline to compare against, and dealers will frequently match or beat that rate if they know you have a competing offer in hand, since they'd rather keep the financing business than lose the deal to an outside lender.
Stretching a car loan from 60 to 72 or 84 months lowers the monthly payment, which can make a more expensive vehicle look affordable on a month-to-month basis, but it also means paying interest for a longer period and often at a higher rate, since longer terms are frequently priced higher by lenders. A longer term also means the car depreciates faster than the loan balance declines for a larger portion of the loan, extending the window where you're upside-down if you needed to sell or trade in early. Whenever possible, choose the shortest term that keeps the payment genuinely comfortable, rather than defaulting to the longest term offered simply because it produces the lowest advertised payment.
Work out the amount financed first: price, plus tax and fees, minus deposit and any trade-in. Then apply the amortisation formula. For $25,000 at 7% over 60 months, r is 0.005833 and the payment is $495.03.
Compute (1+r)^n first, then multiply the principal by r and by that result, and divide by ((1+r)^n - 1). For the example, (1.005833)^60 is about 1.4176, giving $25,000 x 0.005833 x 1.4176 / 0.4176 = $495.03.
Interest each month is the outstanding balance times the monthly rate. On the first payment that is $25,000 x 0.005833 = $145.83, leaving $349.20 to reduce the principal. The split shifts toward principal every month after that.
Yes, proportionally, because interest is charged on what you borrow. Putting down another $5,000 cuts the financed amount to $20,000, reducing the payment to about $396.02 and saving roughly $940 of interest over the term.
It lowers the monthly payment but costs more overall, and it raises the risk of negative equity, where you owe more than the car is worth. Cars depreciate faster than a long loan pays down, which is why 72 and 84 month terms are risky.
Insurance, registration, fuel, servicing and tyres. The loan payment is usually well under half the true monthly cost of running a car, which is why affordability should be judged on total running cost.
A car is a major purchase, and the loan is a significant financial commitment. By understanding the factors that influence your monthly payment and using tools to calculate it beforehand, you can shop with confidence, negotiate more effectively, and drive away in a car you can comfortably afford. For official guidance on this topic, see the CFPB's auto loan guidance.
The fastest way to lower a car payment is not always choosing the longest term. A longer term reduces the monthly payment but can increase total interest and leave you owing more than the car is worth. Test down payment, trade-in value, rate, and term together before you shop, then compare the monthly payment against insurance, fuel, maintenance, and registration costs.
Run scenarios in the Car Loan Calculator, and use the Loan Affordability Calculator to check whether the payment fits your income.
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