The 5 biggest ISA mistakes you need to avoid

Here’s how to become a winning ISA investor.

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.

It’s that magic day of 5 April, and our ISA allowance is rolling round to the new 2017-18 limit of £20,000. Whether you’re starting out with your first ISA or looking forward to adding a new year’s worth of investing to your existing total, there are some key mistakes you should avoid.

Shares, not cash

Around 75% of ISAs taken out each year are cash ISAs. Sure, it’s good to not pay tax on your savings interest, but in these days of super-low interest rates, the tax you’re saving is tiny compared to what you could be losing by not investing in shares. 

If you invest in top FTSE 100 dividend-paying shares, it’s not hard to get yourself income of 4% to 5% or better from dividends alone, and over the long term you’re very likely to enjoy share price appreciation too — an investment in the FTSE 100 at inception in 1984 would have grown nearly sevenfold (plus dividends).

Do it now

Do you think “I’ve got all year to do it“? Or “I’m young, I can leave that ISA lark until I’m older“? Let’s assume a 40-year working life. Thanks to the miracle of compounding, £1,000 invested in your first year at an annual return of 6% would end up worth more than £10,000. But £1,000 invested five years before you retire would get you only £1,340. Early years of investing are worth far more than later years.

And if you keep putting off your start, you’ll be surprised how quickly the year comes round again, and you won’t have time (or the money) to make the most of your allowance.

Don’t over-trade

Charges for buying and selling shares are pretty low these days, but on a transaction of around £1,000 they can still amount to a couple of percent — proportionally less the bigger your trade. That might not sound like much, but it soon adds up, and if you spend the year making multiple buys and sells, especially at relatively low volumes, you’re likely to wipe out any benefits from investing in a Stocks & Shares ISA.

Warren Buffett famously said that if you wouldn’t hold a share for 10 years, you shouldn’t hold it for 10 minutes — and the fact that the vast majority of short-term traders lose money over the long term shows he’s right.

Get rich quick?

The biggest cause of over-trading is probably the desire to get rich quick, and that can be a fatal strategy when it comes to investing in shares. “What’s the next big flyer going to be?“, people often ask me when they find out what my job is, but the simple answer is that I have no idea. And neither does anyone else, beginner and expert alike.

No, if you follow the gambler’s mentality of always looking for a big win, you’ll almost certainly fail. The way to go is to see investing as becoming a part owner of a handful of great business, and seek out shares with great long-term potential.

Reinvest your dividends

I’ll finish with one of my favourite investing statistics. According to the Barclays Equity-Gilt study, if you’d invested £100 in the UK stock market in 1945 it would have grown to around £9,000 after adjusting for inflation — more than 90 times your original investment. But if you’d reinvested all your dividends in new shares too, you be sitting on an inflation-adjusted pot of around £180,000.

Alan Oscroft has no position in any shares mentioned. The Motley Fool UK has recommended Barclays. 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

Santa Clara offices of NVIDIA
Investing Articles

£5,000 invested in Nvidia stock 6 months ago is now worth…

Nvidia stock's taking a breather at the moment. But it could be getting ready for its next move higher, says…

Read more »

British coins and bank notes scattered on a surface
Investing Articles

I hold Lloyds. Is it madness to buy Barclays shares too?

Harvey Jones is keen to buy Barclays shares but wonders whether he's simply doubling down, given that he already holds…

Read more »

Asian man looking concerned while studying paperwork at his desk in an office
Investing Articles

It’s time we all took a long, cold look at the Lloyds share price

The Lloyds share price has been good to Harvey Jones, making him a huge fan of the FTSE 100 bank.…

Read more »

Warren Buffett at a Berkshire Hathaway AGM
Investing Articles

Warren Buffett didn’t retire early. But could his investing wisdom help you do so?

Warren Buffett's wisdom from decades of stock market investing is actionable even for a modest investor who simply aims to…

Read more »

Young female hand showing five fingers.
Investing Articles

5 compelling investment ideas for a Stocks and Shares ISA in 2026

Edward Sheldon discusses some ideas to consider for a Stocks and Shares ISA and highlights a UK stock that could…

Read more »

Man writing 'now' having crossed out 'later', 'tomorrow' and 'next week'
Investing Articles

Is this the best time to buy shares in a long time?

Earlier this week, Bill Ackman stated on X that this is the best time to buy shares in a long…

Read more »

A senior man and his wife holding hands walking up a hill on a footpath looking away from the camera at the view. The fishing village of Polperro is behind them.
Investing Articles

£1,000 buys 35 shares in an incredibly reliable FTSE 100 dividend stock

Despite falling 72% from their highs, shares in this FTSE 100 company have been an incredibly reliable source of dividend…

Read more »

Warren Buffett at a Berkshire Hathaway AGM
Investing Articles

This is what Warren Buffett has to say about passive income — and I’m listening!

While searching for new ways to earn passive income, our writer takes to heart sage advice from the Oracle of…

Read more »