How We Calculate: Methodology & Sources

The formulas behind our calculators and the sources we rely on — independent and transparent.

IndependentWe sell no financeNo commissionMaths based on FCA rules & the Consumer Credit Act 1974

Every calculator on this site uses standard, published finance formulas, and we show exactly how they work. Here's the maths, the assumptions, and the sources behind the figures.

How we work out monthly payments

We convert the APR to a monthly rate, then amortise the amount you finance over the term.

The monthly rate is (1 + APR)^(1/12) − 1. The amount financed is the price minus your deposit. For HP and loans we spread the whole amount over the term; for PCP we defer the balloon (GMFV) to the end, which is what keeps the monthly lower.

The core formula

Monthly = amount financed × monthly rate ÷ (1 − (1 + monthly rate)^−term). For PCP we subtract the present value of the balloon from the amount financed first. The total amount payable is your deposit + every payment + any balloon and fees.

How we work out APR, settlement and the rest

The reverse-APR, settlement, overpayment and affordability tools all use the same present-value maths.

APR: we solve for the rate that makes your payments' present value equal the amount financed.
Settlement: the present value of the remaining payments at your contract rate, reflecting the statutory interest rebate.
Overpayment: we re-run the schedule with your extra payment and compare the interest and months.
Affordability: we work backwards from a monthly budget to an indicative amount.

Our sources

We base our maths and our rights content on the regulator and the law, not on lenders.

The Financial Conduct Authority (FCA) for affordability rules and the motor finance redress scheme.
The Consumer Credit Act 1974 for early settlement, the rebate of interest, and voluntary termination.
The UK Supreme Court ruling of 1 August 2025 for the commission-disclosure position.

What the figures are — and aren't

Our results are estimates based on the figures you enter, to help you compare — not a quote or financial advice.

Your real deal depends on the lender, your credit and the car. For regulated help, contact MoneyHelper or the Financial Ombudsman Service. We update our facts as the FCA scheme develops.

Frequently asked

How accurate are your car finance calculators?

They use standard, published amortisation formulas and the figures you enter, so they're accurate for comparing deals. They're estimates, not quotes — your real payment depends on the lender, your credit and the car.

What sources do you use?

We base our maths and rights content on the FCA, the Consumer Credit Act 1974 and the UK Supreme Court's 1 August 2025 ruling — the regulator and the law, not lenders. We're funded by ads, so we stay independent.

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How we work out monthly payments

We convert the APR to a monthly rate, then amortise the amount you finance over the term.

The core formula

How we work out APR, settlement and the rest

The reverse-APR, settlement, overpayment and affordability tools all use the same present-value maths.

APR: we solve for the rate that makes your payments' present value equal the amount financed.

Settlement: the present value of the remaining payments at your contract rate, reflecting the statutory interest rebate.

Overpayment: we re-run the schedule with your extra payment and compare the interest and months.

Affordability: we work backwards from a monthly budget to an indicative amount.

Our sources

We base our maths and our rights content on the regulator and the law, not on lenders.

The Financial Conduct Authority (FCA) for affordability rules and the motor finance redress scheme.

The Consumer Credit Act 1974 for early settlement, the rebate of interest, and voluntary termination.

The UK Supreme Court ruling of 1 August 2025 for the commission-disclosure position.

What the figures are — and aren't

Our results are estimates based on the figures you enter, to help you compare — not a quote or financial advice.

Your real deal depends on the lender, your credit and the car. For regulated help, contact MoneyHelper or the Financial Ombudsman Service. We update our facts as the FCA scheme develops.