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MONEY GUIDE

How to Calculate How Much Car You Can Afford: Guide

The example is $5,000 of take-home pay at 15% — a $750.00 max payment, a $38,331.51 loan, a $45,331.51 car — plus the five reverses. Four steps, worked line by line, and the 20/4/10 rule as the stricter alternative.

The formula, in one paragraph

How much car you can afford comes down to four numbers. Multiply your monthly take-home pay by 15% for the max monthly payment. Multiply that payment by the annuity factor for your loan term and APR for the max loan. Add your down payment and trade-in for the max car price. The example is $5,000 of take-home pay at 15%, a $5,000 down payment, a $2,000 trade-in, 60 months at 6.5% APR: a $750.00 max payment, a $38,331.51 loan, a $45,331.51 car — A $30,000 car costs $450.02 a month — under budget by $299.98.

Step 1: Your take-home pay and the 15% rule

Start with what lands in your bank account each month, after tax. The rule of thumb is 15% of that number: take-home × 15 / 100. On $5,000 a month, that is $750.00. The 15% is the ceiling, not the target. On $4,000 a month the max payment is $600.00 and the max price is $37,665.21. At 10% the max price is $32,554.34; at 20% it is $58,108.68.

Step 2: From a monthly payment to a max loan

The monthly payment is what the loan buys. The link is the annuity factor: f = (1 − (1+r)^−n) / r, where r is the monthly rate and n is the term in months. At 6.5% APR over 60 months the factor is 51.1087 — one dollar a month buys $51.1087 of loan. The max loan is the max payment times the factor: $750.00 × 51.1087 = $38,331.51. At 72 months the max loan is $44,616.49; at 36 months it is $24,470.62. At 3% APR it is $41,739.27, at 9% it is $36,130.03.

Step 3: From a max loan to a max car price

The max car price is the max loan plus what you pay up front: max price = max loan + down + trade-in. At the defaults that is $38,331.51 + $5,000.00 + $2,000.00 = $45,331.51. The down payment and the trade-in count the same way — both are cash toward the price. With no cash up front, the max price is just the max loan: $38,331.51. The same $30,000 car with no cash up front needs a $30,000.00 loan and costs $586.98 a month with $5,219.07 of interest, against $450.02 and $4,001.28 with the $7,000 of cash.

Step 4: Check the car you are eyeing

Take the price of the car you want and subtract the down payment and the trade-in for the target loan: $30,000.00 − $5,000.00 − $2,000.00 = $23,000.00. Divide by the factor for the target monthly payment: $23,000.00 / 51.1087 = $450.02. Multiply by the term and subtract the loan for the total interest: $450.02 × 60 − $23,000.00 = $4,001.28. Compare the payment with the max: $750.00 − $450.02 = $299.98, so the $30,000 car is under budget by $299.98 a month. A $50,000 car costs $841.34 with $7,480.66 of interest — over by $91.34, so it does not fit.

Step 5: The 20/4/10 rule — the stricter alternative

The 15% rule is the usual rule of thumb, but the 20/4/10 rule is stricter: put 20% down, take a term of 4 years or less, and keep the payment at 10% or less of your gross monthly income. On $5,000 of take-home pay the 10% payment is $500.00 a month, which buys a $25,554.34 loan and a $32,554.34 car at 6.5% over 60 months. This calculator does not model the 20/4/10 rule: it is a stricter check you apply yourself.

Working backwards: the five reverses

Sometimes the question runs the other way. For a $1,000.00 a month max payment at 15%, the take-home pay is $6,666.67 (exact $6,666.6667). To afford a $50,000 car at 15%, the take-home pay is $5,608.96 (exact $5,608.9625): at $5,608.96 the max payment is $841.34. The down payment for a $50,000 car at $750.00 a month is $9,668.49 (exact $9,668.4903): $9,668.49 + $2,000.00 + $38,331.51 = $50,000.00. The term for a $50,000 car at $750.00 a month is 69 months (exact 68.8385 months): at 69 months the payment is $748.55, at 68 months $757.64. The max APR is 1.80% (exact 1.8033%): at 1.80% the payment is $749.94, at 1.81% $750.12.

What changes the answer

Four things move the answer: the take-home pay, the percentage, the term, and the APR. The term moves the loan: 36 months gives a $31,470.62 max price and a $704.93 payment, while 72 months gives a $51,616.49 max price and a $386.63 payment — but the 72-month term costs $4,837.24 of interest against $2,377.37. The APR moves it as well: at 9% the max price is $43,130.03 and the payment is $477.44, while at 3% the max price is $48,739.27 and the payment is $413.28.

What NOT to do

Do not use your gross salary: the rule is 15% of take-home pay, after tax. Do not stretch the term to fit the car: a 72-month term buys a $51,616.49 car on the same payment, but you pay $4,837.24 of interest on the $30,000 car. Do not forget the rest of the car: insurance, gas, and maintenance are not in the 15% — a $750.00 payment with $200.00 of insurance is really $950.00 a month of car.

Max payment = take-home × pct / 100; factor = (1 − (1+r)^−n) / r; max loan = max payment × factor; max car price = max loan + down + trade-in; target loan = target − down − trade-in; target payment = target loan / factor; total interest = target payment × term − target loan

That box is the whole formula.

Worked example: $5,000 take-home, 15%, $5,000 down, $2,000 trade-in, 60 months at 6.5%

Step 1: max payment $5,000 × 15 / 100 = $750.00.
Step 2: factor 51.1087; max loan $750.00 × 51.1087 = $38,331.51.
Step 3: max price $38,331.51 + $5,000.00 + $2,000.00 = $45,331.51.
Step 4: target loan $30,000.00 − $5,000.00 − $2,000.00 = $23,000.00; target payment $23,000.00 / 51.1087 = $450.02.
Step 5: total interest $450.02 × 60 − $23,000.00 = $4,001.28.

Answer: under budget by $299.98 a month — max car price $45,331.51; the $30,000 car costs $450.02 a month.

Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum.

Cite this guideBright Side Kit. “How to Calculate How Much Car You Can Afford: A Step-by-Step Guide.” Method: max payment = take-home × pct / 100; factor = (1 − (1+r)^−n) / r; max loan = max payment × factor; max price = max loan + down + trade-in. Example: $5,000 take-home, 15%, $5,000 down, $2,000 trade-in, 60 months at 6.5%, $30,000 car → max payment $750.00, factor 51.1087, max loan $38,331.51, max price $45,331.51, target loan $23,000.00, target payment $450.02, interest $4,001.28, under budget by $299.98. Reverses: $6,666.67 (exact $6,666.6667); $5,608.96 (exact $5,608.9625); $9,668.49 (exact $9,668.4903); 69 months (exact 68.8385 months); 1.80% (exact 1.8033%). Bright Side Kit. "How to Calculate How Much Car You Can Afford: Guide" https://brightoolbox.com/guides/how-to-calculate-how-much-car-you-can-afford/ Accessed October 25, 2026.
Planning estimate, not professional advice: the max price is an affordability estimate — confirm the loan terms and the insurance cost before you buy.

Frequently asked questions

How do I calculate how much car I can afford?

Four steps: 15% of your take-home pay for the max payment, times the annuity factor for the max loan, plus your down payment and trade-in for the max car price. On $5,000 of take-home pay at 15%, the max payment is $750.00 a month, the factor at 6.5% over 60 months is 51.1087, the max loan is $38,331.51, and with $5,000 down and a $2,000 trade-in the max car price is $45,331.51.

What is the 15% rule for buying a car?

Spend no more than 15% of your monthly take-home pay on the car payment. On $5,000 a month of take-home pay, that is $750.00 a month. The 15% is the ceiling, not the target: a cheaper payment is always fine. The stricter 20/4/10 rule — 20% down, a term of 4 years or less, a payment of 10% or less of gross monthly income — gives a $500.00 payment and a $32,554.34 car on the same numbers.

How much car can I afford on $5,000 a month?

A $45,331.51 car, on a $750.00 a month payment. 15% of $5,000 is $750.00 a month, which buys a $38,331.51 loan at 6.5% over 60 months (factor 51.1087), and with $5,000 down and a $2,000 trade-in the max price is $45,331.51. A $30,000 car costs $450.02 a month — under budget by $299.98.

How much do I need to earn to afford a $50,000 car?

$5,608.96 a month of take-home pay at 15% (exact $5,608.9625). The $50,000 car costs $841.34 a month, and $841.34 / 0.15 = $5,608.96. Or put $9,668.49 down at $750.00 a month (exact $9,668.4903), or take 69 months (exact 68.8385 months), or find a 1.80% APR (exact 1.8033%).

Is it better to pay cash for a car?

If the down payment and trade-in cover the price, yes — no loan, no payment, no interest. A $7,000 car is covered by the $5,000 down payment and the $2,000 trade-in: the target loan is $0.00, the payment is $0.00, and the interest is $0.00. For the loan itself, see the car loan payoff calculator.

Does a longer loan term mean I can afford a more expensive car?

Yes — but it costs more interest. At 36 months the max loan is $24,470.62 and the max price is $31,470.62; at 72 months the max loan is $44,616.49 and the max price is $51,616.49. On the $30,000 car, the 36-month term costs $2,377.37 of interest and the 72-month term costs $4,837.24. For whether to lease or buy, see the lease vs buy car calculator.

Related calculators

GuidesEvery guide on the site. Car Affordability CalculatorHow much car can you afford? Car Loan Payoff CalculatorHow fast can you pay the loan off? Lease vs Buy Car CalculatorLease it or own it?