The magic of compound interest

By - Ciaran
07.12.23 04:05 PM
Compound Interest

The magic of compound interest

Saving your first £1m
Have you ever heard of compound interest? It's basically the interest you earn on your interest, and it can grow at an ever-increasing rate. Let me give you an example: If you invest £10,000 at 5% per year (compounded annually), you'll have £10,500 at the end of year 1, £11,025 at the end of year 2, and £11,576.25 at the end of year 3. This means that the interest accrued increases year-on-year, with year 1 generating £500 in interest, year 2 generating £525, and year 3 generating £551.25.

The key to compound growth is getting started and staying invested for the long-term. The longer you remain invested, the greater the potential returns on what you've already invested. Here's another example to show you the power of compound interest: Let's say you invest £10,000 per year at 7% interest. The longer you remain invested, the quicker your money grows. 


For example, your first £100k would take 7.44 years to save, but the final £100k (going from £900k to £1million) would only take 1.34 years. This is due to the interest you earn on interest, which helps your portfolio grow at an increasing rate year to year.

Years to achieve £1m

It's important to consider your return assumptions when thinking about compound interest. As your returns increase, the time it takes to save the next £100k will decrease. For example, starting from £0 at 2% per year, it would take 9.04 years to save the first £100k. But if you assume a return of 12% per year, the time taken to save the first £100k falls to 6.43 years.


Another thing to consider is your portfolio size. If you assume a return of 2% per year, starting from £0, the first £100k will take 9.04 years to save. However, if you started with £1 million, the first £100k would only take 3.24 years to save.


I hope this helps you understand the power of compound interest and how it can help you grow your investments over time.

Compound Interest Table

Sam, Startup. ‘Compound the Pound, Blog Post’. EBI Evidence Based Investing, 24 March 2023. https://ebi.co.uk/blog/compound-the-pound/.


The value of units can fall as well as rise, and you may not get back all of your original investment.