We have some exciting news to share! The Motley Fool UK has now become The Twelfth Magpie -- an independent, UK-owned company, led by our long-serving UK management team — Mark Rogers, Chris Nials and Heather Adlington. In practical terms, it’s the same team you know, now fully focused on serving our UK readers and members.

Just as importantly, our approach remains unchanged: long-term, jargon-free, and on your side. This site is our new home, and there will be extra tweaks made across the coming few days as we settle in. So if anything looks a little off, please bear with us!

The content of this article was relevant at the time of publishing. Circumstances change continuously and caution should therefore be exercised when relying upon any content contained within this article.

2 crucial pieces of investment advice to build your retirement portfolio

You absolutely need to understand compound interest to succeed as an investor.

You’re reading a free article with opinions that may differ from The Motley Fool’s Premium Investing Services. Become a Motley Fool member today to get instant access to our top analyst recommendations, in-depth research, investing resources, and more. Learn More.

Knowing what to invest in is of paramount importance. But it is also vitally important to know how to invest. Here are two things that I think you absolutely have to understand to succeed in the market.

Understand the power of compound interest

Albert Einstein once said: “Compound interest is the most powerful force in the universe”. He may have been right. The benefit of compound interest can be summarised as follows: the more money you have, the more money you will make in the future, assuming you deploy your capital correctly. This is a pretty simple idea, but one that many people seem to have trouble grasping. 

XXX

One key impact of compound interest is that those people who start to save earlier, and invest their savings earlier, will benefit disproportionately compared to those who don’t. An initial £10,000, invested at 5% per annum, will compound to £16,407.09 after 10 years, assuming no deposits or withdrawals – a gain of £6,407.09. 

However, investing that £10,000 for 20 years at the same interest rate will yield £27,126.40 for a gain of £17,126.40. You can see that doubling the savings period increased the overall gain by a factor of 2.67.

Investing that £10,000 for a period of thirty years at 5% will compound to £44,677.44 for a gain of £34,677.44. Tripling the saving period increased the final gain by a factor of 5.41.

So, it’s not just a case of the longer you save, the more money you will have, it’s that your money will compound faster and faster the longer you save. For this reason, it is advisable to start an ISA, and take advantage of pension matching schemes, as soon as possible.

Beware of people saying “this time it’s different”

In October 1929, Irving Fisher of Yale University, one of the most highly-respected economists of his day, declared that stock prices had “reached what looks like a permanently high plateau”. Nine days later, the stock market was hit by the most devastating crash in the history of the US in an event dubbed ‘Black Tuesday’. 

“This time it’s different” is one of the most dangerous phrases that an investor can hear. Some version of this statement will typically accompany the formation of a market top. It is supposed to mean that, although valuations may be expensive by historical standards, investors should buy anyway because a paradigm shift has made the old standards irrelevant.

In the dot.com bubble of the late 1990s, it was believed that new technologies were going to usher in an era of unprecedented economic expansion that would push valuations to brand new heights. 

Economists and commentators seem to have an uncanny ability to make such pronouncements right before the market breaks. In 1999, journalist James K. Glassman and economist Kevin Hassett co-authored a book titled Dow 36,000: The New Strategy From Profiting From The Coming Rise In The Stock Market.

Its core thesis was that stocks would soon be considered as risk-free as bonds and that the market would price them accordingly. When this happened, the fair value of the Dow would be around 36,000. Twenty years later, the all-time high for the Dow stands at 27,398 (set earlier this year).

When someone tells you that this time is different, assume it probably isn’t.

Neither Stepan nor The Motley Fool UK have a position in any of the shares mentioned. Views expressed on the companies mentioned in this article are those of the writer and therefore may differ from the official recommendations we make in our subscription services such as Share Advisor, Hidden Winners and Pro. Here at The Motley Fool we believe that considering a diverse range of insights makes us better investors.

More on Investing Articles

Friends and sisters exploring the outdoors together in Cornwall. They are standing with their arms around each other at the coast.
Investing Articles

£503 buys 14 shares in this FTSE 250 stock that returned 23.9% annually for the last 15 years

This FTSE 250 stock has averaged a huge return for 15 years. At today's price, £503 buys 14 shares. But…

Read more »

Black woman using loudspeaker to be heard
Investing Articles

£1,000 buys 25 shares in this FTSE 100 stock that’s returned 29.2% annually for the last 10 years

This FTSE 100 mining stock has returned close to 30% a year for a decade. At 3,995p, £1,000 buys 25…

Read more »

Female student sitting at the steps and using laptop
Investing Articles

Down 47%, is this growth stock finally worth buying in May?

With a £288m order book and a hidden pipeline of defence and nuclear contracts, is this growth stock now too…

Read more »

House models and one with REIT - standing for real estate investment trust - written on it.
Investing Articles

2 REITs yielding 7%+ to consider for passive income in 2026

A REIT backed by the NHS and another backed by Tesco and Sainsbury's with both yielding 7%+. Here's why I'm…

Read more »

Woman riding her old fashioned bicycle along the Beach Esplanade at Aberdeen, Scotland.
Investing Articles

Just 97 shares of this UK dividend stock generate £238 in passive income

A 5.7% yield, £238 in passive income from just 97 shares, and one of the most divisive dividend stocks on…

Read more »

ISA coins
Investing Articles

£10,000 in an ISA generates a second income of…

The London Stock Exchange is home to some of the world's most generous dividends. But how big a second income…

Read more »

Shot of a senior man drinking coffee and looking thoughtfully out of a window
Investing Articles

Expert recommendations: 2 top income stocks yielding 7%+!

With yields of 7.2% and 7.8% respectively, these two income stocks are catching the eyes of institutional analysts. Should investors…

Read more »

Illustration of flames over a black background
Investing Articles

3 top income-focused stocks to buy in May 2026, according to experts

Looking for a stock to buy for income in May 2026? Experts have flagged these three UK dividend shares as…

Read more »