Flat Rate vs APR on Car Finance: What Is the Difference?

A quote showing 5% flat interest can cost substantially more than one showing 5% APR. The percentages measure borrowing differently. Use the APR to compare rates, then compare the total amount payable and the payment schedule.

A car finance quote might show a 5% flat rate and an APR closer to 10%. That does not mean two interest charges are being added together. They are different ways of describing the cost of the same borrowing.

Why the percentages differ

Flat interest

A flat interest rate calculates interest using the amount originally borrowed throughout the agreed term. The calculation does not reduce that starting amount as you make repayments.

For a straightforward agreement without a balloon payment, the basic calculation is: amount borrowed multiplied by the annual flat rate, multiplied by the number of years. That gives the interest for the full term before any fees.

It is easy to work out, but the percentage needs context. By the final year, you have already repaid much of the borrowing. A rate still calculated from the original amount cannot be compared directly with a rate that reflects the timing of those repayments.

APR

APR stands for Annual Percentage Rate. It expresses the cost of credit as an annual rate, taking account of interest, relevant compulsory charges and when payments are due.

APR is a comparison measure, rather than a separate type of finance. An agreement calculated using flat-rate interest can still have an APR. The lender has not necessarily changed how it charges interest simply because both figures appear on the paperwork.

Our guide to how APR works in car finance covers the wider terminology you may see on a quote.

£10,000 over four years: 5% flat versus 5% APR

Suppose you borrow £10,000 over four years at an annual flat rate of 5%. This is an illustration, not a finance offer. Assume 48 equal monthly payments, the first due one month after the money is advanced, with no fees and no final balloon payment.

• Interest for each year: £10,000 × 5% = £500.
• Interest over four years: £500 × 4 = £2,000.
• Total loan repayments: £10,000 + £2,000 = £12,000.
• Monthly repayment: £12,000 ÷ 48 = £250.

With those payment assumptions, the equivalent APR is approximately 9.6%. The 5% flat rate and 9.6% APR describe that same £250 monthly repayment schedule.

For comparison, borrowing £10,000 over the same 48 months at 5% APR, with no fees or balloon payment, would cost approximately £229.79 a month. Total repayments would be about £11,029.93, including £1,029.93 interest. The final instalment may need a small rounding adjustment.

In this example, confusing 5% flat with 5% APR would mean overlooking roughly £970 of additional interest. The deposit is excluded from both calculations: these figures compare repayments on the £10,000 borrowed, not the entire purchase price of the car.

Why doubling the flat rate is only a rough guide

Doubling can give a rough sense of why a small flat percentage is not necessarily cheap, but it is not a dependable conversion. The term, payment dates, fees and any large final payment affect the calculation.

You also cannot calculate a loan's total interest by multiplying its APR by the starting balance and the number of years. In the example above, 9.6% × £10,000 × four would produce a completely different figure from the actual £2,000 interest.

Ask for the APR on the written quotation. If you have been given only a flat rate and a monthly payment, you do not yet have enough information to compare the offer properly.

Compare the written quotations

Before deciding which quote is cheaper, check that both cover the same car price, deposit, amount of credit and repayment period. A larger deposit can make an expensive agreement look comfortable each month, while a longer term spreads payments over more months.

Write down these figures from each personalised quotation:

1. Cash price and deposit: distinguish your own cash or part-exchange equity from any dealer contribution.
2. Amount of credit: check whether extras have been added to the borrowing.
3. APR: use the rate offered to you, rather than assuming an advertised representative rate applies.
4. Payment schedule: record the number of instalments and any different first or final payment.
5. Total amount payable: check what the stated total includes, especially the deposit and any optional final payment.

If the terms differ, ask for comparable quotations. Our guide to choosing a car finance term explains why a lower monthly payment can come with a higher overall cost.

Ask the provider to show, in pounds, everything you would pay on the route you intend to take. Check that the explanation matches the written quote and pre-contract information.

Allow for fees and the PCP final payment

APR includes relevant compulsory credit charges, but it does not tell you every possible cost of using or returning the car. Look separately for late-payment charges, early settlement terms, optional products, and any mileage or condition charges that could apply on return.

Ask whether an arrangement fee is paid upfront or added to the credit, and whether an option-to-purchase fee is due to become the owner. If a warranty or another extra is financed, check the price and the interest attributable to borrowing that extra amount.

With PCP, a substantial optional final payment is left until the end. Monthly payments therefore do not repay the whole amount needed to own the car. Interest is generally charged on the financed amount including the deferred balance, so a smaller monthly figure does not by itself mean less interest.

If ownership is your aim, include the optional final payment in your comparison. If you intend to return the vehicle, compare the deposit and instalments alongside the mileage allowance and return conditions. The distinction is covered in our HP and PCP guide.