Shopping by monthly payment is how many buyers end up with seven-year loans on cars they cannot really afford. A better approach is to set the budget first and let it decide the price. This calculator starts from either your income or the payment you are comfortable with, works backward through the loan, sales tax, fees, down payment and trade-in, and tells you the most car that budget buys — along with whether the deal passes the 20/4/10 test.
How to use the car affordability calculator
- Choose whether to start from your income or from a monthly payment.
- In income mode, enter your gross annual income, the share of income you want to spend on the car and your expected insurance, fuel and upkeep. In payment mode, enter the monthly payment you can afford.
- Enter the APR and loan term you expect.
- Add your down payment, trade-in equity, sales tax rate and fees, and choose whether tax and fees are financed or paid in cash.
- Read the maximum price, the 20/4/10 checks and the table showing what the same payment buys over other terms.
How the price is worked out
The payment first becomes the largest loan it can repay:
Then the loan, cash and trade-in are turned back into a price. When tax and fees are financed, with tax rate t charged on the price minus the trade-in:
Worked example
You earn $75,000 and follow the 10% guideline, with $250 a month for insurance and fuel. You plan a 48-month loan at 7%, with $5,000 down, 6% sales tax and $600 of fees.
Car budget: 75,000 ÷ 12 × 10% = $625; payment = 625 − 250 = $375
Loan: 375 × (1 − 1.005833−48) ÷ 0.005833 = $15,660.08
Price: (15,660.08 + 5,000 − 600) ÷ 1.06 = $18,924.60, or about $18,900
Sales tax $1,135.48; total interest $2,339.92. Down payment is 26% of the price — the deal passes all three 20/4/10 checks.
What the same payment buys over different terms
At $375 a month and 7% APR with the same down payment, tax and fees:
| Term | Car price | Total interest |
|---|---|---|
| 36 months | $15,600 | $1,355.08 |
| 48 months | $18,900 | $2,339.92 |
| 60 months | $22,000 | $3,561.75 |
| 72 months | $24,900 | $5,004.58 |
| 84 months | $27,500 | $6,653.52 |
The longer terms look like more car for the same money, but interest climbs steeply, and long loans often carry higher APRs than this table assumes. The car also loses value faster than an 84-month loan is repaid.
Making the budget go further
Improve the rate
A better credit score, a credit union pre-approval or a shorter term can each cut the APR. Every point lower adds a few hundred dollars of buying power on a typical loan.
Cut the costs around the car
Negotiate dealer fees, decline add-ons you do not need, and compare insurance quotes before you buy — a cheaper policy frees up payment room.
Consider nearly new
A two- or three-year-old car has already absorbed its steepest depreciation, so the same budget buys more car and you are less likely to end up owing more than it is worth.
Once you have a price, the auto loan payment calculator models the full deal and the car loan calculator compares terms in detail.
Estimates only. Lender approval depends on your credit and income, and tax rules for trade-ins and fees vary by state.
Frequently asked questions
What is the 20/4/10 rule for buying a car?
It is a rule of thumb: put at least 20% down, finance for no more than four years, and keep total car costs — payment, insurance and fuel — under 10% of gross income. It keeps you from owing more than the car is worth and leaves room in the budget for other goals.
How much car can I afford on $75,000 a year?
Under the 20/4/10 guideline, 10% of $6,250 a month is $625 for all car costs. If insurance and fuel take $250, about $375 is left for the payment. At 7% for 48 months with $5,000 down, 6% sales tax and $600 of fees, that supports a car of roughly $18,900.
Why does a longer loan let me afford a more expensive car?
Spreading the same payment over more months lets you borrow more, but you pay more interest and stay upside down longer. At $375 a month, going from 48 to 84 months raises the price you can afford from about $18,900 to $27,500, while interest nearly triples.
Should I count insurance and fuel?
Yes. A more expensive car usually costs more to insure, register and maintain. The income mode subtracts these running costs before working out the payment, which gives a more realistic price.