What’s compound interest?

Understand what compound interest means and how it's calculated

When you take out a loan, you usually have to pay off the sum you borrowed - the principal - and a percentage of that amount as interest. This is normally done via one or several payments made over a pre-set timescale.

Compound interest works slightly differently. Instead of paying the same amount of money at regular intervals, you’ll have to pay an ever-increasing amount of money on each payment date.

The reason for this is that your interest payment will be based on the principal plus the prior interest payment you made. This is easy to understand when you see it in an example.

Let’s say someone borrowed £10,000 that had to be paid back at the end of ten years, with an annual interest rate of 2 per cent per.

With a normal loan that would mean the borrower would have to pay interest of £200 for each of those ten years. Add that to the principal and, at the end of ten year period, the borrower would have to pay back £12,000.

If someone took the same loan but had to pay compound interest, things would look slightly different:

Calculating compound interest on borrowing £10K for 10 years with 2% annual rate

As you can see, the borrower will end up having to pay £12,189.94, slightly more than the regular loan which would have ended up costing £12,000.

A difference of £189.94 isn’t too bad but if a loan has a higher and more frequent interest rate, it can make borrowing very, very expensive.

Learn more:

Investing 101

How to invest in stocks and shares

More terms

Forward pricing

Mutual funds are traded on a forward pricing basis, meaning the price you see will be different to the price you may trade at.
Read more

Margin call

Learn what a margin call stands for in financial terms.
Read more

Real Estate Investment Trust (REIT)

An investment trust specialised in investing in commercial property such as parking garages or GP offices.
Read more

Balance sheet

A summary of a company's finances, including its assets, liabilities and shareholder equity.
Read more

Stock Exchange

A physical/digital place where stockbrokers and traders can buy and sell securities.
Read more

Net asset value

Mutual funds and investment trusts are priced on their net asset value (NAV).
Read more

Dirty price

The total price payable on the purchase of a gilt. It’s calculated as the clean price plus accrued interest.
Read more

Net Income (NI)

The money a firm is left with from sales after subtracting taxes and different business costs.
Read more

Leverage

A method of trading using borrowed money that usually involves a very high level of risk.
Read more

You’re just minutes away from commission-free investing

When you invest, your capital is at risk