How do interest rates and mortgages work, explained simply

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For most people a mortgage is the biggest loan they will ever take on, and interest is the price of borrowing it. The jargon can make it feel complicated, but the core ideas are simple. This guide explains them without assuming any financial background. It is general information: mortgage products, rules and taxes differ between countries, so check the details where you live.

Interest is rent on money

When you borrow money, the lender wants paying for letting you use it. That payment is interest, usually expressed as a percentage of the amount borrowed per year.

Borrow more, or for longer, and you pay more interest in total.
A higher rate means more interest on the same amount.
Lenders charge more to riskier borrowers, because they are more likely not to be paid back.

Where the rate comes from

Central banks, such as the Bank of England, the European Central Bank or the US Federal Reserve, set a key policy rate to steer inflation. When they raise it, borrowing generally becomes more expensive across the economy; when they cut it, cheaper.
Your mortgage rate is not the same as that rate. Lenders add their own margin, and the rate you are offered also depends on the loan size compared with the property's value, your income, your credit history and the type of deal.

What a mortgage is

A mortgage is a loan secured on a property. If you stop paying, the lender can ultimately take and sell the home to recover the money. That security is why mortgages usually cost less than unsecured loans.

The deposit is the part of the price you pay yourself. A bigger deposit usually unlocks better rates because the lender is taking less risk.
Loan to value is the loan as a share of the property's price. A smaller share generally means a better rate.
The term is how long you have to repay, often decades. A longer term lowers the monthly payment but usually means paying more interest overall.

How repayments work

On a typical repayment mortgage, each monthly payment covers that month's interest plus a slice of the original loan.

Early on, the balance is large, so most of each payment is interest and only a little reduces the debt.
As the balance shrinks, less interest is due each month, so more of the same payment goes towards the loan itself.
By the end, the loan is fully repaid.

This gradual paying down is called amortisation. An interest-only mortgage is different: you pay just the interest, and the whole loan is still owed at the end, so you need a credible plan to repay it.

Fixed or variable

Fixed rate. The rate stays the same for a set period, so your payment is predictable. If rates fall, you do not benefit until the deal ends, and leaving early can trigger a charge.
Variable or tracker rate. The rate moves, often following the central bank's rate or the lender's own standard rate. Payments can fall or rise.
When a deal ends, many loans move on to a higher default rate, so it is worth reviewing your options before then.

Customs vary by country: in some places fixing for the full life of the loan is common, while in others short fixed periods are the norm.

A simple example of why the rate matters

Imagine two loans of the same size and term, one with a rate one percentage point higher than the other. That single point raises every monthly payment and, over a long term, can add up to a substantial sum. Comparing rates and fees together, rather than the headline rate alone, gives the clearest picture.

Sensible habits

Look at the total cost, including arrangement fees, not just the monthly figure.
Ask whether you could cope if rates rose at the end of a fixed deal.
Use your lender's or a regulator's calculators, and consider an independent, regulated adviser for big decisions.
Talk to your lender early if you are struggling. Most have options, and debt advice charities can help free of charge.

Have a question about mortgages or how rates feed through? Ask it in the comments.