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What Is Compound Interest?

Explained: Compound interest is the eighth wonder of the world. It's interest paid on interest.

In this financial guide:

Explained: Compound interest is the eighth wonder of the world. It’s interest paid on interest.

Albert Einstein famously said that compound interest is the eighth wonder of the world.

Basically, compound interest means ‘interest on interest’.

For example, let’s imagine you have $100 today and you decide to put it in the bank, where it earns 10% interest in one year.

After one year, you still have your original $100. But you also have 10% in interest, which works out to be $10.

So in total, you have $110 after one year.

Let’s say that you put all of the $110 back into the bank, who promises to pay you another 10% after a year.

This time, the bank will pay you 10% interest on your $110.

So at the end of the second year, you will have your $110 plus an extra 10% interest. Which works out to be $11.

In total, you have $121.

After two years, you have earned $21 in interest, with $1 of interest paid on the interest you earned in year one. That is interest on interest.  

This might sound like a small amount of money but if you invest your money in the bank year…after year…after year…for a very long time, you will eventually have a huge amount of money.

That’s because your original $100 is earning $10 interest each year, but your interest is also earning more and more of its own interest year.

Mortgages and credit cards are compound interest in reverse. Meaning, the bank gives you some money now, which you must repay. Then, you pay interest over many years.

That’s why Albert Einstein also said, “The person who understands compound interest, earns it – the person who doesn’t, pays it.

Try our Compound Interest Calculator!

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Owen Raszkiewicz

Owen is the Chief Investment Officer of Rask Invest and Founder of Rask. Since founding The Rask Group in 2017 in the hillside suburb of Upwey, Victoria, Owen has overseen the growth of the Rask platform to over 200,000 investor followers. Today, Owen oversees the Rask Analyst team, which helps more than 4,000 Aussies build core portfolios from ETFs and shares, he hosts Australia's biggest investing podcast, The Australian Investors Podcast, appears on Rask's other channels, covering Property, Business and Finance; and leads Rask Education - our education platform which has enrolled over 25,000 Australians into free finance courses. Prior to founding Rask, Owen was an investment analyst at the highly regarded managed funds research business and a writer/analyst for one of the most well-known share market publications. Owen’s formal qualifications include a Master of Applied Finance and Master of Financial Planning from Kaplan Professional, Bachelor of Technology (Information Systems) from Swinburne University of Technology, Advanced Diploma of Financial Services (Financial Planning) and Diploma of Mortgage Broking Management. He's also completed level 1 of the Chartered Financial Analyst (CFA) program.

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