Hire purchase calculator UK: the arithmetic behind the monthly payment

What the calculation needs, and what it reveals

1. Three numbers, and the fourth is the answer. The amount financed is the cash price less your deposit and less any part exchange, plus anything added in such as an administration fee or a warranty. The term is the number of monthly payments. The rate is the APR. From those the monthly payment follows, and so does the total amount payable, which is the payment multiplied by the term plus the deposit and the option to purchase fee. If a quote does not let you reconstruct that, a number is missing.
2. Flat rate and APR are not comparable. A flat rate charges interest on the original balance for the whole term even though the balance is falling, so the true cost is close to double the flat figure. The APR is the standardised measure and includes compulsory fees, which is why it is the one lenders must quote and the one to compare. Seeing a strikingly low rate is usually a sign it is a flat rate, and converting it is the difference between comparing two quotes and being told two stories.
3. Affordability is a different calculation entirely. An affordability calculator works backwards from your income and committed outgoings to a payment you could sustain, which is what a lender's own assessment does. It is not the same as a payment calculator and it answers a different question. The lender's version also stresses the figure, asking whether the payment survives a change in your circumstances, which is why its answer is often lower than the one you would reach yourself.
4. Proof of income is what the calculation rests on. Every payment figure assumes income the lender can verify. Where income is cash, irregular, or newly self employed, the usual evidence is several months of bank statements or filed accounts rather than payslips. A firm offering finance with no proof of income at all is either not assessing affordability, which the rules require, or is pricing the uncertainty into a total you should read before you sign.

Common questions

How do I calculate vehicle finance on hire purchase?

By amortising the amount financed over the term at the APR. There is no deferred payment, so the balance repays to zero and the total is the payments plus the deposit and the option to purchase fee.

What is the difference between flat rate and APR?

A flat rate charges interest on the original balance throughout even as it falls, so the true cost is close to double. The APR is the standardised comparable measure and includes compulsory fees.

Affordability car finance: what does a car affordability calculator do?

It works backwards from income and outgoings to a sustainable payment, which is what a lender's own assessment does. It answers a different question from a payment calculator.

Can I get car finance without proof of income?

FCA rules require an affordability assessment based on sufficient information. Where payslips do not exist the usual evidence is bank statements or filed accounts.

Why does the dealer's figure differ from mine?

Usually fees added into the amount financed, a different term, or a flat rate quoted against your APR. Reconstruct the total amount payable and the difference becomes visible.

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