Picture two people with identical debts and identical spare cash each month. One pays off her smallest balance first — the debt snowball. The other throws everything at his most expensive debt — the debt avalanche. Same income, same starting point. A year later, one of them has handed noticeably less money to lenders, and it isn't always the one who feels most in control.

Both methods are simple, and both work. The interesting part is choosing the one that survives contact with a real month: a car repair, a birthday, a payday that arrives two days late.

What each method actually involves

Start the same way for both. List every debt with its balance, its interest rate and its minimum payment. Keep paying the minimum on everything, and send all remaining spare cash to a single target. The only question is which target you pick.

Debt snowball

1. Order your debts from smallest balance to largest, ignoring interest rates.
2. Pay the minimum on every debt.
3. Put every spare pound towards the smallest balance.
4. When it clears, roll its minimum payment into the next smallest and repeat.

Debt avalanche

1. Order your debts from highest interest rate to lowest.
2. Pay the minimum on every debt.
3. Put every spare pound towards the most expensive debt.
4. When it clears, roll the whole payment onto the next highest rate.

The rolling is where the power sits. A £40 minimum you no longer owe becomes £40 of extra firepower, and the pile grows with every balance you clear.

The maths: why the avalanche usually costs less

Interest is charged on balances, so a pound sitting on a 24.9% credit card costs you considerably more than a pound on an 8.9% personal loan. Attacking the expensive debt first shrinks the costliest part of your borrowing, which means less interest accrues and more of each payment chips away at the actual capital.

Take an illustrative example. Three debts: a credit card at £4,200 on 24.9%, a second card at £1,100 on 21.9%, and a personal loan at £3,700 on 8.9%. You have £300 a month to throw at the pile. The snowball clears the £1,100 card first — probably within four months — then rolls onto the big card. The avalanche goes straight for the £4,200 card. By the time both plans reach the same place, the snowball has paid extra interest on the largest, most expensive balance, and that gap compounds slowly month by month.

How big is the difference? Narrow when your rates are close together or your balances are similar. Wider when you're carrying a high-rate card alongside a cheap loan, or when one balance dwarfs the others.

Where the snowball earns its keep

The snowball is a motivation tool, and motivation is not a soft issue. If you have four or five smaller balances — a catalogue account, a buy-now-pay-later plan, a small overdraft, a store card — clearing one completely in a couple of months does something that a spreadsheet can't. It proves the plan works.

It also suits people who have started and abandoned repayment plans before. If the last three attempts died in month five, the method that gets you a win in month two is probably the better method for you, even if it costs a little more interest. A plan you finish beats a mathematically perfect plan you quit.

Where the avalanche is worth the discipline

Choose the avalanche when the rate gap is wide — say a card in the twenties against a loan under 10% — or when one balance is much larger than the rest and sits at a high rate. It's also the right call if you're not particularly moved by milestones and just want the cheapest exit.

One warning: the avalanche can feel slow. If your target debt is £4,000 and shrinking by £300 a month, you'll spend a long stretch seeing no finished lines on your list. Track the interest saved instead. Watching the monthly interest charge fall from £87 to £40 is its own kind of progress.

A hybrid that suits a lot of people

You don't have to pick a side. Clear the smallest balance first if it will take three months or less, take the win, then switch to the avalanche for the rest. You get early momentum and cheap maths.

Another version: order by size, but if two balances are close in size, target the one with the higher rate. A £900 card at 24.9% should always beat a £950 card at 19.9%.

UK details that change the picture

• Falling minimum payments. Credit card minimums are usually a percentage of the balance, so they drop as you pay down. Keep paying the original amount rather than letting the minimum shrink, or you'll lose momentum without noticing.
• Balance and money transfers. A 0% balance transfer can beat both methods outright — if the fee is modest and you clear the balance before the promotional period ends. Check your eligibility before applying, since a rejected application leaves a mark on your credit file.
• Overdrafts. Arranged overdraft pricing is often higher than people assume. Work out the annual cost in pounds before deciding it's your cheapest debt.
• Loan early repayment charges. Check your credit agreement before overpaying a personal loan. Some allow it freely, some charge.
• Priority debts first. Rent or mortgage, council tax, energy, water and court fines come before credit cards and catalogue accounts. Ordering tricks are for non-priority debt.
• Free, impartial help. StepChange, National Debtline, Citizens Advice and MoneyHelper all offer free guidance. If your repayments are genuinely unaffordable, that conversation matters far more than the order in which you pay. For anything involving your home or a court order, take regulated professional advice.

Which clears balances faster — and what to do next

If you keep your total monthly payment the same and stick to the plan, the avalanche clears your debt in the same number of months or fewer, and costs less interest. That's the honest answer on speed. The snowball rarely wins the race on paper, but it wins on completion, and an unfinished plan is the most expensive option of all.

So decide this week:

1. Write down every balance, rate and minimum payment. Check your credit report with Experian, Equifax or TransUnion to make sure nothing is missing.
2. Work out your spare monthly amount, then add a realistic buffer so you're not derailed by a normal life event.
3. Pick your target and set a standing order for the day after payday.
4. Review every three months. When a balance clears, move the whole payment to the next target.
5. Send windfalls — a bonus, a tax rebate, money from selling something — straight to the target before it becomes spending money.

Either method will get you out. The one you'll still be running in month nine is the one that gets you out soonest.

Photo: RDNE Stock project / Pexels