Car Affordability Calculator
Work out the max car price you can afford from income, debts, down payment and loan terms — before you visit the dealer.
Follows the 15/20/4 rule: payment ≤ 15% of gross income, total debts ≤ ~36%. Check your actual loan offer — dealer rates and insurance will change the final numbers.
Why affordability math beats sticker price
Dealerships sell cars by monthly payment, and that framing is deliberate: almost any price becomes 'affordable' if you stretch the loan far enough. A $40,000 car at 84 months is a similar monthly payment to a $30,000 car at 48 months — but the total cost, the interest paid, and the years you spend owing more than the car is worth are wildly different.
The antidote is to decide your budget before you walk in, based on your income and debts — not on what the dealer says you qualify for. Lenders approve payments that maximise their profit, not your financial health. An approval for a $700/month payment does not mean a $700/month payment is wise for your budget.
This calculator works backwards: from what you can safely pay each month, through your actual loan terms, to the maximum price that fits. That number is your ceiling. Everything — the car, the trim, the add-ons — must fit under it, and knowing it in advance turns the dealership conversation from persuasion into arithmetic.
How it works
- 1Enter income and debts
Gross monthly income and your other monthly debt payments.
- 2Add down payment and trade-in
Cash down plus the realistic value of your current car.
- 3Set loan term and APR
Use a pre-approved rate if you have one.
- 4Get your ceiling
Max affordable car price, max monthly payment, and total cost.
The formula
The 15/20/4 rule, explained
The 15/20/4 rule is the most quoted car-buying guideline for a reason: each number defends against a specific trap. The 15% payment cap keeps the car from crowding out rent, savings and the rest of life. Note it means 15% of gross income — on a $6,500/month income, that is $975, before insurance and fuel.
The 20% down payment protects against depreciation. New cars lose roughly 15–25% of their value in the first year or two; with 20% down, you are never 'underwater' — owing more than the car is worth — which matters if the car is totaled or you need to sell. Gap insurance exists precisely because most buyers skip this step.
The 4-year maximum term limits interest and matches the loan to the car's reliable life. Stretching to 72 or 84 months can add thousands in interest and keeps you paying long after the warranty expires — a risky combination of payments plus repair bills. The table below shows what term length does to the same purchase.
How loan term changes a $25,000 loan at 7.5% APR
| Term | Monthly payment | Total interest | Total paid |
|---|---|---|---|
| 36 months | $778 | $2,993 | $27,993 |
| 48 months | $604 | $4,000 | $29,000 |
| 60 months | $501 | $5,056 | $30,056 |
| 72 months | $432 | $6,074 | $31,074 |
| 84 months | $383 | $7,148 | $32,148 |
The 84-month term 'saves' $395 a month versus 36 months but costs an extra $4,155 in interest — and you are still paying in year seven. Run your own numbers in this calculator and compare the total cost row; it is the most honest line in car buying.
How your debts change what you can afford
Your car payment doesn't exist in isolation — lenders and financial planners both look at your debt-to-income ratio (DTI): total monthly debt payments divided by gross monthly income. Most lenders want DTI under 36–43% for auto loans, and the conservative end of that range is where this calculator sits.
The maths is unforgiving: on a $6,500/month income, 36% is $2,340 of total monthly debt capacity. If rent, student loans and credit cards already take $1,800, only $540 remains for a car payment — and the 15% income cap ($975) doesn't override it. The binding constraint is whichever is lower.
This is why paying down high-interest debt before car shopping is so powerful. Eliminating a $300/month credit card minimum doesn't just save interest — it directly raises your affordable car price by thousands, because every freed dollar of monthly capacity becomes loan capacity. The Debt Snowball Calculator can help plan that payoff order.
Down payment and trade-in strategy
Down payment and trade-in are the two levers that raise your affordable price without raising your payment. Every $1,000 of down payment is $1,000 less financed — saving roughly $20/month on a 60-month loan at typical rates, plus the interest you never pay.
For trade-ins, do your homework separately from the purchase negotiation. Get a written offer from an online buyer or a second dealer before you walk in — that number is your floor. Dealers often inflate the trade-in offer while padding the new car's price, so negotiate the two transactions as if they were independent: agree the car's price first, then the trade-in value.
If you owe more on your current car than it's worth (negative equity), rolling that balance into the new loan is usually a mistake — it inflates the new loan, deepens the underwater hole, and the cycle repeats at the next trade-in. Better to pay down the difference or keep the current car longer.
Frequently asked questions
How much car can I afford?+
A widely used guideline is the 15/20/4 rule: spend no more than 15% of gross monthly income on the car payment, put at least 20% down, and finance for no more than 4 years (48 months). This calculator applies the 15% payment cap plus a total-debt ceiling of ~36% of income, then works backwards through your loan terms to a maximum car price.
What is the 15/20/4 rule for buying a car?+
Put at least 20% down, finance for no more than 4 years, and keep total monthly car expenses under 15% of gross income. Each part protects you: the down payment keeps you from owing more than the car is worth, the short term limits interest, and the payment cap keeps the car from crowding out savings and other goals.
How do my other debts affect car affordability?+
Lenders look at your debt-to-income ratio — total monthly debt payments divided by gross monthly income — and most prefer it under 36–43%. This calculator caps your car payment so your total debts stay near 36%. If your existing debts are already high, the affordable car price drops sharply, which is the maths telling you to pay down debt first.
Should I include my trade-in in the calculation?+
Yes — trade-in value works exactly like a down payment: it reduces the amount you must finance. Enter your car's realistic private-party or trade-in value (check a pricing guide, then expect the dealer to offer somewhat less). A larger trade-in or down payment directly raises the car price you can afford without raising the payment.
Is a longer loan term (72–84 months) a good idea?+
Rarely. Longer terms lower the monthly payment but dramatically increase total interest, keep you 'underwater' (owing more than the car's worth) for years, and often outlast the warranty period. This calculator shows total cost including interest so you can compare terms directly — the 60-month and 72-month totals are usually an eye-opener. The Car Loan Calculator can model payoff schedules in more detail.
What interest rate should I use?+
Use the APR you have actually been quoted or pre-approved for — rates vary widely by credit score, from roughly 5% for excellent credit to 10%+ for fair credit on new cars (used-car rates run higher). Getting pre-approved before visiting the dealer gives you a real number and bargaining leverage.
Does the calculator include insurance and maintenance?+
No — it covers the purchase price, loan amount, payment and interest. Insurance, fuel, maintenance and registration are ongoing ownership costs that can add 30–60% on top of the payment. Budget those separately: get an insurance quote for the specific car before you buy, since rates vary enormously by model.
Should I buy new or used?+
From a pure affordability standpoint, a 2–3 year old used car is usually the sweet spot: it has taken the steepest depreciation hit but still has modern safety features and often remaining warranty. New cars lose roughly 15–25% of value in the first year or two. Whatever you choose, run the numbers here first — the payment cap doesn't care about the odometer.
