How credit card interest works
How APR becomes a daily charge, the grace period that means £0 interest, why the minimum payment costs years — and how to clear a card faster.
The one rule that matters most
If you pay your statement balance in full every month, you pay no interest at all on purchases. Credit card interest only becomes your problem the moment you carry a balance from one month to the next. Everything below is about what happens when you do.
How APR turns into a daily charge
The headline number is the APR (Annual Percentage Rate) — for UK cards typically 19%–35%. But cards don't charge it once a year. Most charge interest daily: they convert the APR to a daily rate (roughly APR ÷ 365), apply it to your balance every day, and add up the total on your statement. Because yesterday's interest becomes part of today's balance, it compounds — interest earning interest.
| Approximate daily rate | 24.9% ÷ 365 ≈ 0.068% a day |
| One month of interest, if the balance stays around £3,000 | roughly £61 |
These are rough figures. Many cards work interest out on your average daily balance over the statement cycle, and the exact charge depends on your card's terms — treat this as a ballpark, not the precise amount. The takeaway holds either way: if your payment is below the monthly interest, the balance grows, and paying only a shrinking minimum can keep a debt like this going for years.
The grace period: up to ~56 days interest-free
Purchases have an interest-free grace period — the gap between the start of your statement cycle and the payment due date, usually up to about 56 days. Pay the full statement balance by the due date and you never pay interest on those purchases. Pay only part of it, and the grace period collapses: interest is charged from the transaction date on the unpaid amount.
The minimum-payment trap
The monthly minimum payment is usually the greater of a small percentage of the balance (often 1%–2.5%) plus that month's interest, or a floor like £5. It's designed to be affordable — which is exactly the problem. Most of it covers interest, and because it's a percentage of a shrinking balance, the payment falls every month and progress slows to a crawl.
| Paying the minimum only | Over 20 years · ~£6,000 interest |
| Paying a fixed £150 a month | About 2 yr 3 mo · ~£900 interest |
Same card, same balance — fixing your payment instead of letting it shrink saves over £5,000 and roughly 18 years. Try it with your own figures →
How to pay less interest
- Pay a fixed amount, not the minimum — even a little above the first minimum clears the card years sooner.
- Pay more than the monthly interest, always — below that, the balance never falls.
- Consider a 0% balance transfer. Moving the balance to a 0% card pauses the interest while you pay it down, for a one-off fee. Check whether it's worth it with the balance transfer calculator.
- Tackle the highest-APR card first if you have several (the “avalanche” method saves the most interest).
The expensive corners: cash advances & penalties
Not all borrowing on a card is equal. Cash advances — withdrawing cash, and some cash-like transactions — typically carry a higher APR, a fee, and no grace period, so interest starts immediately even if you pay in full. Missing a payment can trigger a fee and, on some cards, a higher penalty rate, as well as a mark on your credit file. If money is tight, talk to your lender before you miss a payment.
Frequently asked questions
How is credit card interest calculated?
Most UK cards charge interest daily. They take your APR, convert it to a daily rate (roughly APR ÷ 365), and apply it to your balance each day, then add the total to your statement each month. Because it compounds, the interest itself starts earning interest if you don’t clear the balance.
How can I avoid paying any credit card interest?
Pay your statement balance in full by the due date every month. Purchases get an interest-free grace period of up to around 56 days, so clearing the full balance means you’re charged £0 interest. Interest only starts when you carry a balance from one month to the next.
Why does paying the minimum take so long?
The minimum payment is usually a small percentage of the balance plus that month’s interest, so most of it just covers interest and barely touches what you owe. And because the minimum shrinks as the balance falls, progress slows to a crawl — a typical £3,000 balance at around 25% APR can take over 20 years on minimums alone.
Does a 0% card really charge no interest?
On the promotional balance, yes — a 0% purchase or balance-transfer deal charges no interest for a set period. But the rate reverts to the standard APR when the deal ends, and balance transfers usually carry a one-off fee. The goal is to clear the balance before the 0% period finishes.
What is a cash advance and why is it more expensive?
Withdrawing cash on a credit card (or some cash-like transactions) is a cash advance. It usually has a higher APR than purchases, charges a fee, and — crucially — has no grace period, so interest starts the day you take the money out, even if you pay in full.
See exactly how long your card will take to clear — and what the minimum really costs.
Credit card payoff calculator →