How credit card interest really works (and the minimum-payment trap)
A credit card is one of the most misunderstood tools in your wallet. Handled one way, it’s free short-term borrowing that also protects your purchases. Handled another way, it quietly becomes one of the most expensive debts you can carry. The good news: the rules that decide which one you get are simple, and nobody teaches them — so here they are.
This is information, not financial advice. It explains how credit card interest and protections work in the UK. It doesn’t recommend any particular card or lender. If debt is becoming unmanageable, free help is available from MoneyHelper, StepChange and Citizens Advice.
The most important rule: the interest-free window
When you buy something on a credit card, you’re not usually charged interest straight away. Most cards give you an interest-free period — often up to around 56 days — between the purchase and the date your bill is due.
Here’s the crucial part: if you pay off your full statement balance by the due date every month, you pay no interest at all. None. The card company makes its money from the retailer, and from people who don’t clear the balance. Do this, and you’re using the bank’s money free for up to two months, every month.
Miss it — pay less than the full balance — and interest kicks in, often on the whole balance and sometimes back to the purchase date. That’s the fork in the road.
What APR actually means
The APR (Annual Percentage Rate) is the yearly cost of borrowing on the card, including interest and standard fees. A typical purchase APR might be somewhere around 24%, though it varies by card and applicant.
Interest is usually worked out daily on what you owe and added monthly, so it compounds — you can end up paying interest on your interest. That’s why a balance you’re only chipping away at grows so stubbornly.
The minimum-payment trap
Every statement shows a minimum payment — often something like “the greater of 1% of the balance plus interest, or £5”. It’s the least you can pay to avoid a late-payment mark. It is not a sensible amount to pay.
Minimum payments are deliberately low, and they’re partly a percentage of the balance — so as your balance falls, the minimum falls too. The result is that paying only the minimum can stretch a fairly ordinary balance into years and years of repayments, and multiply the original cost in interest.
The fix is almost embarrassingly simple: pay a fixed amount that’s more than the minimum, and keep it fixed even as the minimum drops. It’s the single biggest lever on how much a debt costs you — and our calculator shows the difference in black and white.
See what the minimum-payment trap costs with the credit card calculator →
“Persistent debt” — the rule in your favour
Regulators noticed how many people get stuck, so card firms now have to watch for persistent debt. Broadly, if over an 18-month period you’ve paid more in interest, fees and charges than you’ve actually repaid off what you borrowed, your provider must contact you and help you clear it faster — and eventually offer ways to repay that cost you less. If you ever get one of these letters, it’s a prompt to act, not to panic: engage with it.
The upside: Section 75 protection
There’s a genuine perk to putting spending on a credit card — Section 75 of the Consumer Credit Act. For anything with a cash price over £100 and up to £30,000, your card provider is jointly liable with the retailer if something goes wrong: the goods never arrive, the company goes bust, the holiday is cancelled, the item is faulty and the seller won’t play ball.
That means you can claim from your card company directly. A few things worth knowing:
- It applies to the item’s price, and you only need to have put part of the payment on the card (even a deposit) to be covered for the whole cash price.
- It’s why a credit card can be safer than a debit card for big or risky purchases — flights, furniture, a deposit to a tradesperson.
- Below £100, a separate scheme called chargeback may still help, though it’s not a legal right in the same way.
Use the card for the protection, then clear the balance in full — you get the safety net and pay no interest.
The whole thing in a nutshell
A credit card is a brilliant servant and a terrible master. Pay in full, use the interest-free window, and lean on Section 75 for big buys — and it costs you nothing while working for you. Slip into paying only the minimum, and it becomes an expensive debt that lingers for years.
If you’re carrying a balance now, don’t despair — see what paying a little more each month does to the timeline. It’s usually a bigger difference than people expect.
Try the credit card payoff calculator →
Last checked 23 July 2026. Section 75 thresholds (£100–£30,000) and the persistent-debt framework are current; individual card APRs and minimum-payment formulas vary by provider.
Sources
Just so you know: this guide is information and journalism, not financial advice, and we don't recommend specific financial products. Your circumstances are your own — if you need personal advice, speak to a suitably qualified adviser. Information was correct at the "last updated" date above but things change; always check the linked primary sources.