PocketProofA dealership or lender will happily approve you for more car than you can actually afford — approval just means they think you're likely to pay it back, not that the payment fits comfortably in your life. Those are two very different questions, and only one of them is yours to answer.
This guide walks through a simple rule of thumb for car affordability, how your credit score affects the interest rate you'll actually be offered, and includes a calculator at the bottom that puts real numbers to both.
The 20/4/10 rule
It's the most commonly cited rule of thumb for car buying, and it's a good default if you don't have a strong reason to deviate from it:
- 20% down. Put down at least 20% of the purchase price in cash or trade-in value. This protects you from being "upside down" — owing more than the car is worth — since new cars lose a big chunk of their value in the first year.
- 4-year loan, maximum. Keep the loan term at 48 months or less. Longer terms lower your monthly payment, but they also mean paying far more in total interest and staying underwater on the loan for longer.
- 10% of income, total. Your total monthly transportation costs — loan payment plus insurance — shouldn't exceed 10% of your gross (pre-tax) monthly income.
Why 48 months, not 72 or 84?
Stretching a loan to 72 or 84 months is now common, and it's usually sold as "affordability" — but it mostly just moves the cost around. A longer term means more total interest paid, and it takes longer before you owe less than the car is worth. If a car only "fits your budget" at 72+ months, the honest read is usually that the car is out of budget, not that the term solved the problem.
Why your credit score matters so much here
Your credit score doesn't just affect whether you get approved — it directly sets your interest rate (APR), and on a car loan that difference compounds into real money. Someone with a 620 score financing the same $25,000 car as someone with an 800 score can end up paying thousands more in interest over the life of the loan, for the identical vehicle.
| Credit score | Tier | Avg. APR — New | Avg. APR — Used |
|---|---|---|---|
| 781–850 | Super prime | ~5.3% | ~6.8% |
| 661–780 | Prime | ~6.5% | ~8.8% |
| 601–660 | Nonprime | ~9.8% | ~13.5% |
| 501–600 | Subprime | ~13.5% | ~18.5% |
| 300–500 | Deep subprime | ~15.8% | ~21.5% |
Used cars almost always carry a higher rate than new cars at the same credit tier — lenders see more risk in a vehicle with unknown history and faster ongoing depreciation. If your score is on the edge of a tier, it can be worth paying down a card balance or waiting a billing cycle before applying; even a small score bump can shift you into a meaningfully better rate.
Car affordability calculator
Enter your numbers below. The calculator applies the 10% (or 15%) of gross income guideline, subtracts an estimated insurance cost, looks up an APR based on your credit score and whether the car is new or used, and works backward to a maximum loan amount and total affordable purchase price.
What car can you afford?
Defaults are pre-filled with an example: $75,000/year income and an 830 credit score.
Estimates only, for planning purposes. Actual rates and approved amounts depend on the specific lender, your full credit profile, the vehicle, and current market conditions. Get pre-qualified with a couple of lenders before you shop to know your real rate.
Working through the example: $75,000 income, 830 credit score
Plugging those numbers into the calculator above with the defaults (48-month term, conservative 10% budget, $150/month estimated insurance, $5,000 down):
- Gross monthly income: $6,250
- Total monthly auto budget (10%): $625
- Max loan payment after insurance: $475/month
- Credit score 830 → super prime tier → roughly 5.3% APR on a new car
- That works out to a maximum loan of a little over $20,000 over 48 months
- Add the $5,000 down payment: an affordable price of roughly $25,000–$26,000
Stretching to a 60-month term at the same payment level raises the affordable loan amount, since the payment is spread over more months — but check the total interest figure the calculator gives you before deciding that's worth it. A bigger number today often means paying meaningfully more for the same car over the life of the loan.
Want the full formula-by-formula breakdown of that $75,000 example, plus how it scales at other salaries? See our detailed 20/4/10 rule breakdown.
What to do with this number before you shop
- Get pre-qualified, not just pre-approved. Pre-qualification with a bank or credit union gives you a real rate to compare against whatever the dealership offers, without a hard credit inquiry. Credit unions in particular often beat dealer-arranged financing for the same credit tier.
- Negotiate the price, not the payment. A dealer can hit almost any monthly payment target by stretching the term — that's not a win. Agree on the total price first, financing second.
- Don't skip the insurance quote. Get an actual insurance estimate for the specific make/model before you commit — it varies more than people expect, and the calculator above is only as accurate as that number.
- Watch for add-ons. Extended warranties, gap insurance, and dealer add-ons are often rolled into the loan itself, quietly increasing both your loan amount and your interest cost. Evaluate them separately, on their own merits — not as a rounding error on the monthly payment.
If the number the calculator gives you feels tight relative to what you were hoping for, it may be worth building up your down payment a bit longer — see our guide on cutting monthly expenses to free up extra savings, or revisit your plan with zero-based budgeting so the car payment has a real, deliberate place in your monthly plan rather than squeezing out other goals.
