Understanding loan repayments and interest

The basic promise of a loan

When you borrow, a lender gives you a lump sum now in exchange for scheduled repayments later. Part of each payment covers the cost of borrowing-the interest-and part reduces what you still owe, called the principal. The lender's business model depends on charging enough interest to cover their funding costs, risk, and operations. Your job as a borrower is to understand how much you will pay in total, how flexible the contract is, and what happens if you pay faster than required.

Amortisation in plain language

Most consumer loans and mortgages use an amortising schedule. Early in the term, a larger slice of each payment goes to interest because interest is calculated on the outstanding balance, which is still high. As the balance shrinks, more of each payment goes to principal. That is why the first few years of a long mortgage can feel as if you are "hardly paying it off" even though your monthly payment is large-the mechanics are normal, not a trick.

Our loan and mortgage calculator lets you plug in amount, rate, and term to see a representative monthly payment. Remember that variable rates, fees, introductory deals, and insurance bundled into payments can all change the real cost compared with a simple model.

Why extra payments reduce total interest

Overpayments shrink the principal sooner than the original schedule, so future interest accrues on a smaller balance. Even modest regular overpayments can shorten the term and cut the total interest noticeably on long-lived debt. Not every loan allows free overpayments; some fixed-rate products charge early repayment fees or cap how much you can overpay each year. Always read your agreement or ask the lender before relying on this strategy.

Explore scenarios with the extra payment impact tool, which illustrates how lump sums or higher monthly amounts change interest and term in a simplified setup.

APR and comparing offers

The Annual Percentage Rate (APR) is designed to express the yearly cost of borrowing in a comparable way, often including some fees as well as the interest rate. Comparing APRs across similar products and terms is usually more informative than comparing headline interest rates alone. For savings products, you may see AER instead, which is the analogous idea for interest you earn.

Multiple debts: order of attack

If you have several balances, two common strategies are the avalanche (highest interest first) and snowball (smallest balance first) methods. Avalanche often minimises total interest paid; snowball can help motivation by clearing accounts quickly. Our debt payoff calculator compares simplified timelines side by side so you can see the trade-off in numbers.