FTSE 100 investing: are you making this key mistake?

Investing in FTSE 100 (INDEXFTSE: UKX) stocks? Be careful not to make this mistake as it could hurt your returns.

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.

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.

When it comes to investing in the FTSE 100, there are plenty of common mistakes a lot of investors make on a regular basis. For example, buying high and selling low, panicking when the market falls, and not diversifying are three of the most typical.

Yet another mistake that could be just as dangerous is putting too much focus on price-to-earnings (P/E) ratios when picking stocks. Could this be hurting your performance?

The P/E ratio

The P/E ratio is widely-used in stock market analysis. A simple ratio which shows the price of a stock per £1 of earnings, the ratio gives an indication of whether value is on offer. The general idea is that the lower the P/E ratio, the more value that’s on offer.

The P/E ratio does have several things going for it. For starters, it allows investors to compare valuations for different companies. Secondly, it’s very easy to calculate (share price divided by earnings per share). However, the ratio is not perfect and it’s important to realise a stock with a low P/E isn’t necessarily a bargain. Similarly, a stock with a high P/E ratio shouldn’t necessarily be avoided.

Focus on quality

One problem with the P/E ratio is that it doesn’t tell you anything about a stock’s ‘quality.’ For example, it tells you nothing about revenue or earnings growth, or the company’s financial health. And, like many things in life, when it comes to stocks, sometimes you’re better off paying a little more for a higher-quality stock than investing in a low-quality stock simply because it’s cheap. As Warren Buffett says: “It’s far better to buy a wonderful company at a fair price than a fair company at a wonderful price.”

Cheap stocks can stay cheap

The problem with cheap stocks that have low P/E ratios is that they’re often cheap for a reason. Perhaps earnings are declining or a dividend cut is on the horizon. And cheap stocks can often stay cheap (and get even cheaper) for a long time, which can really hurt your returns.

At the same time, stocks with high P/E ratios can sometimes deliver amazing returns for investors, despite their high valuations. Yes, a high P/E leaves less margin for error, but ignoring a stock just because it’s expensive could be a mistake.

For example, look at FTSE 100 stocks Diageo and Unilever which have been expensive on the basis of their P/E ratio for years now. These two are up 25% and 19%, respectively, over the last year.

By contrast, look at British American Tobacco and ITV. These two have been cheap for years, yet both have performed terribly over the last 12 months returning -20% and -37%, respectively.

The takeaway here is that while the P/E ratio can be useful, it’s not perfect, and putting too much focus on it could be a mistake. When it comes to stock picking, it’s important to look at a broad range of factors and not just valuation.

Edward Sheldon owns shares in Diageo, Unilever and ITV. The Motley Fool UK owns shares of and has recommended Unilever. The Motley Fool UK has recommended Diageo and ITV. 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

Warren Buffett at a Berkshire Hathaway AGM
Investing Articles

Can someone invest like Warren Buffett with a spare £500?

Christopher Ruane explains why an investor without the resources of billionaire Warren Buffett could still learn from his stock market…

Read more »

Investing Articles

Can these 2 incredible FTSE 250 dividend stocks fly even higher in 2026?

Mark Hartley examines the potential in two FTSE 250 shares that have had an excellent year and considers what 2026…

Read more »

Thoughtful man using his phone while riding on a train and looking through the window
Investing Articles

Is 45 too late to start investing?

Investing at different life stages can come with its own challenges -- and rewards. Our writer considers why a 45-year-old…

Read more »

Hand of person putting wood cube block with word VALUE on wooden table
Investing Articles

UK shares look cheap — but the market might be about to take notice

UK shares have traded at a persistent discount to their US counterparts. This can create huge opportunities, but investors need…

Read more »

Investing Articles

This FTSE 100 growth machine is showing positive signs for a 2026 recovery

FTSE 100 distributor Bunzl is already the second-largest holding in Stephen Wright’s Stocks and Shares ISA. What should his next…

Read more »

Investing Articles

I asked ChatGPT for the best FTSE 100 stocks to buy for passive income in 2026 and it said…

Paul Summers wanted to learn which dividend stocks an AI bot thinks might be worth buying for 2026. Its response…

Read more »

ISA Individual Savings Account
Investing Articles

Stop missing out! A Stocks and Shares ISA could help you retire early

Investors who don't use a Stocks and Shares ISA get all the risks that come with investing but with less…

Read more »

Investing Articles

Will Greggs shares crash again in 2026?

After a horrible 2025, Paul Summers takes a look at whether Greggs shares could sink even further in price next…

Read more »