If you have £40 in a bank account, the bank is not holding forty specific pound coins for you in a box with your name on it. It is holding a record that says it owes you £40. The actual money has been lent out to somebody else.
That sounds alarming the first time you hear it, and it is genuinely how the whole system works.
What a bank actually does
A bank's basic business is simple: take in money from people who have some, lend it to people who need some, and keep the difference.
- You deposit £100. The bank pays you, say, 3% interest for the use of it.
- The bank lends that £100 to someone else at, say, 8%.
- The bank keeps the 5% gap. Multiplied across millions of customers, that is a bank.
They keep enough cash on hand for normal day-to-day withdrawals, not for everybody at once. In the UK, if a bank fails, the Financial Services Compensation Scheme protects deposits up to £85,000 per person per institution — which is the safety net that makes the arrangement workable.
The three kinds of card
| Card | Whose money | Minimum age | What happens if you overspend |
|---|---|---|---|
| Prepaid | Money loaded on in advance | Often 6+, with a parent | Payment is simply declined |
| Debit | Money in your bank account | Usually 11+ | Declined, or an overdraft if you have one |
| Credit | The bank's money, borrowed | 18+ | You owe it, and interest starts |
The important line is between the first two and the third. Prepaid and debit cards spend money you already have. A credit card is borrowing, every time you use it. They look identical, they feel identical at the till, and they are not the same thing at all.
What happens when you tap
It feels instant. Quite a lot happens in that second and a half:
- The card sends its details to the shop's terminal over a very short-range radio link.
- The shop's bank asks your bank whether the money is there.
- Your bank checks your balance, considers whether the payment looks like your normal behaviour, and answers yes or no.
- The terminal beeps. Your available balance drops immediately.
- The actual money moves between the banks later — usually a day or two afterwards.
This is why a payment can show as "pending" and why a refund takes days to appear. The message travels instantly; the money strolls after it.
Three rules that stay true for life
- Nobody legitimate ever needs your PIN. Not your bank, not the police, not someone who phones you saying your account is at risk. Nobody.
- Real banks do not create urgency. "Act now or your account will be closed" is the single most reliable sign of a scam.
- If in doubt, hang up and call back on the number printed on your own card. A scammer cannot follow you there.
Kinds of account you will meet
- Current account — the everyday one. Money in, money out, a debit card attached. Little or no interest.
- Savings account — money you are deliberately not spending. Pays more interest; sometimes you must give notice to take money out.
- Junior ISA — a UK savings account for under-18s where the interest is tax-free. A parent opens it, the child takes control at 16 and can withdraw at 18.
Where cash still matters
Card payments are convenient, and that is exactly the problem: they are frictionless. Handing over a £10 note and receiving £4.50 back is a physical event you notice. Tapping is not. Plenty of adults who are perfectly numerate spend more on a card than they would with cash, simply because nothing in the moment says "that was ten pounds". Knowing this about yourself is worth more than any budgeting app.
Questions people ask
- What is the difference between a debit card and a credit card?
- A debit card spends money already in your bank account. A credit card borrows the bank's money, which you then owe and pay interest on if you do not clear it. They look and feel the same at the till but are completely different things.
- What age can you get a bank card in the UK?
- Prepaid cards for children are often available from around age six with a parent's agreement. Bank accounts with a debit card usually start at about eleven. Credit cards require you to be 18.
- What does a bank do with your money?
- It lends most of it to other people. The bank pays you a small amount of interest for the use of your money, charges borrowers more, and keeps the difference. In the UK, deposits are protected up to £85,000 per person per institution.
- Why do refunds take several days?
- The message authorising a payment travels instantly, but the money itself moves between banks afterwards, usually over a day or two. A refund has to go through that slower process in reverse.