Car Affordability Calculator — How Much Car Can You Afford?

Your Finances

Gross Monthly Income

Other Monthly Debts

Down Payment Available

Trade-in Value

Loan Details

Interest Rate

%/yr

Loan Term

months

Est. Monthly Insurance

Max Monthly Car Budget

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Max Car Price

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Monthly Payment

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Loan Amount

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Total Interest

20/4/10 Rule Check

About the Car Affordability Calculator

This calculator helps you find a car price that fits your real financial situation — not just the maximum a lender might approve. It works from two directions: your maximum monthly budget (reverse-engineered to a car price) and the classic 20/4/10 affordability rule, so you can see whether your budget is comfortable or a stretch.

What is the 20/4/10 rule?

The 20/4/10 rule is a widely-used personal finance guideline for car buying: put at least 20% down, finance for no longer than 4 years (48 months), and keep total monthly car costs (payment + insurance) under 10% of your gross monthly income. Meeting all three criteria is a strong sign the car is genuinely affordable for you.

How is the max car price calculated?

The calculator works backwards from your maximum monthly payment. Using your loan rate and term, it solves for the loan principal that produces that payment, then adds your down payment and trade-in to arrive at the maximum car price you can afford within your budget.

Should I use the maximum I can afford?

Not necessarily. The result is a ceiling, not a target. Buying below your maximum leaves room for unexpected repairs, insurance increases, and other financial goals. Many financial advisors suggest targeting 80% of your maximum affordable price as a comfortable budget.

True cost of car ownership

The purchase price is only one part of the true cost of owning a car. Running costs over 3 years often exceed the purchase price for a new car. Before buying, always calculate the total cost of ownership including depreciation, insurance, road tax, fuel, servicing, tyres, and financing costs.

Depreciation — accounts for 40-60% of new car total cost; buy a 2-3 year old car to avoid the steepest drop
Insurance — varies dramatically by driver age, location, and car model; always get quotes before buying
Fuel — at current prices, a car doing 10,000 miles/year at 40 MPG costs approximately £1,700/year
Financing — interest on a PCP or HP deal is a real cost; factor it into your affordability calculation

Financing vs buying outright

Buying a car outright is financially optimal if you have the capital, as you avoid interest charges. However, tying up a large sum in a depreciating asset has an opportunity cost — that money invested might return more than the finance interest rate. The sensible comparison is: finance interest rate vs your expected return on the capital if invested.

0% finance deals — manufacturers sometimes offer 0% APR; these are genuinely free money if the price has not been inflated
Cash vs 0% finance — with 0% finance, invest the capital and use the investment returns to make payments
Opportunity cost — if finance costs 5% APR and you earn 6% on investments, financing is mathematically better
Used vs new — a 2-3 year old car with main dealer service history offers much better value than new; the first owner absorbed the sharpest depreciation

Frequently Asked Questions

What is the 20/4/10 rule for buying a car?

Put at least 20% down, finance for no more than 4 years, and keep total car costs (payment + insurance) under 10% of gross monthly income. Meeting all three is a sign the purchase is comfortably within your means.

How much of my income should go to a car?

A common guideline is to spend no more than 10–15% of your gross monthly income on car payments. Including insurance and running costs, keep total car expenses under 20% of take-home pay.

What is a good monthly car payment?

A good car payment is one that fits comfortably in your budget without crowding out savings or other goals. As a rule of thumb, keep it under 10% of your gross monthly income.

Should I use the maximum loan amount I qualify for?

No. Lenders often approve more than is financially wise. Use this calculator to find a payment that fits your actual budget — not just what you qualify for.

How much should I spend on a car as a percentage of income?

A common guideline is to spend no more than 15-20% of monthly take-home pay on total car costs (payment, insurance, fuel, and tax combined). For the purchase price alone, some advisors suggest a maximum of 35% of annual gross salary. These are guidelines, not rules — someone with low housing costs can safely spend more on a car than someone with a large mortgage.