How much should I spend on a car?
Short version: shop by the total monthly cost of keeping the car on the road, and keep that under 10% of your take-home pay. The sticker price and the payment are both the wrong number to shop by, and under 26 the reason is insurance.
The rule most people quote: 20/4/10
Put 20% down, finance for no more than 4 years, and keep all car costs under 10% of your gross monthly income. It is a rule of thumb, not a law, and it is deliberately conservative. Two adjustments make it usable:
- Use take-home, not gross. Your paycheck is what pays the loan, not your salary.
- The 10% is everything, not just the payment: loan, insurance, fuel, maintenance, registration, and whatever you plan to spend on the car every month.
The number that actually matters
Add these up. This is the figure to shop by:
| Line | Where to get it |
|---|---|
| Loan payment | A loan calculator, at the rate you were actually quoted |
| Insurance | A real quote on the exact car, before you buy it |
| Fuel | Your weekly miles ÷ the car's real-world MPG × local price |
| Maintenance set-aside | Tires, brakes, oil, one surprise. $75–$150/month is a working range for most used cars |
| Registration & taxes | Annual figure ÷ 12 |
| Mods, if you are honest about it | Whatever you have actually spent per month on your last car |
A worked example
Take-home of $2,800/month. Ten percent is $280/month for everything.
If insurance on the car you want quotes at $180/month — not unusual at 21 with a sporty coupe on your own policy — then fuel and a maintenance set-aside eat most of the rest, and the loan payment you can actually carry is close to zero. That is not a trick. It is the reason people at that age end up with a car that owns them.
Two ways out, and both are ordinary:
- Buy a car insurance is cheap on. Get quotes before you shop, on three specific VIN-level cars. The spread between a sedan and a two-door with the same value can be over $100/month, which is worth more than any haggling you will do at the dealer.
- Raise the ceiling honestly. If cars are your main hobby, budgeting 15% of take-home to the car and cutting elsewhere is a real choice, made on purpose. Blowing through 10% by accident is not.
What about the payment being "affordable"?
A payment can always be made affordable by making the loan longer, and the loan getting longer is exactly what makes the car expensive. On $28,000 at 9%, stretching 48 months to 72 drops the payment from $696.78 to $504.72 and raises the interest you pay from $5,445 to $8,339. Same car, $2,894 more, plus two extra years of being underwater. See is a 72-month car loan bad.
The quick self-check
- Write down your take-home for one month. The real number, after everything.
- Multiply by 0.10. That is your all-in car budget.
- Get an insurance quote on the specific car, today, before anything else.
- Subtract insurance, fuel and a maintenance set-aside from step 2. What is left is the payment.
- Work backwards from that payment, at 48 months, at the rate you were actually quoted, to a price.
Most people do this in the opposite order and find out in month three.
Forgenta is a personal finance app that treats a car as what it is: a payment, an insurance bill, a maintenance schedule and a build budget that all come out of the same paycheck. It projects the whole thing forward month by month so you can see the answer before you sign.