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

Synthetic ETFs

An ETF that that reproduces the return of an index through the use of swaps.
Read more

Accounting standards

The rules a company follows when preparing financial statements.
Read more

Equity

The amount of money a company would be left with by subtracting its liabilities from the value of its assets.
Read more

W-8BEN Form

Non-US individuals and businesses may have to file this form for the Internal Revenue Service (IRS), the US tax authority.
Read more

United States Dollar (USD)

The famous greenback our friends in the US use as currency.
Read more

Venture Capital

A type of financing that investors provide to startups, who sometimes announce getting said financing in TechCrunch, to big fanfare.
Read more

Yield curve

A graphical representation of interest rates over time
Read more

Net Income (NI)

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

Exchange-Traded Fund (ETF)

A collection of investments, pooled into a single fund that can be bought and sold on a stock exchange.
Read more

You’re just minutes away from commission-free investing

When you invest, your capital is at risk