How I plan to build a £1 million ISA account

Being able to make a million pounds in the stock market and retire comfortably, is a dream for many investors and it really is possible.

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.

Being able to make a million pounds in the stock market and retire comfortably, is a dream for many investors. 

However, most investors give up before they even start, because they think they face an uphill struggle to reach this life-changing amount of money.

But in reality, it is not impossible to make a million if you follow a strict savings plan and invest your money sensibly. 

A stocks and shares ISA is a great tool to help you achieve this goal. Capital gains and income on investments in an ISA are tax-free, and you don’t even need to declare the gains or dividend income on your tax return. The benefit of this is that you can keep more of the money you earn, and over time, the extra benefits of not having to pay tax really add up.

The power of compounding

The best tool investors have to help them make money in the stock market is compound interest. Albert Einstein once called compound interest the eighth wonder of the world, and it is easy to see why.

Compound interest is effectively the process of your money earning money. For example, if you save £100 and put it in a high-interest savings account paying 5% per annum every month, with no further contributions, the value of your funds will grow into £105.12 over the space of 12 months. That’s £5 interest on your initial investment and an extra 12p interest on the interest you earned throughout the year.

Over the long term, compound interest becomes exceptionally powerful. Over the past 10 years, the FTSE 250 has produced an average annualised return for investors of 9%. According to my calculations, if you took the same £100 from the example above, and invested it in the FTSE 250 at an average annual rate of return of 9%, after one decade it would be worth £241.20 — that’s an increase of 141.2% with absolutely no effort on your part whatsoever.

The road to a million

Compound interest is the primary tool I plan to use to build a £1m ISA account. I am planning on using a combination of the FTSE 250 and FTSE 100 in my ISA because they offer the best of both worlds. The Footsie 250 is mainly comprised of fast-growing mid-caps, while the FTSE 100 is full of blue-chip income stocks. 

According to my calculations, a portfolio comprised 50/50 of these two leading indexes would have produced an average annual total return of around 7% over the past decade.

So, how long will it take me to make a million pounds at this rate of return? 

As I have already filled up my stocks and shares ISA for this year, I am going to use this balance as a starting point for my calculations. Assuming I make the most of my allowance every year going forward, I will be contributing £1,666 a month to my savings pot. My number crunching shows that if I can maintain this rate of saving every year, assuming an average annual rate of return of 7% and no taxes on my money, I reckon I will have a £1m ISA account with 21 years.

It might not be the most exciting investment strategy around, but who needs excitement when you can build a £1m ISA account?

Rupert Hargreaves owns no share mentioned. The Motley Fool UK has no 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

UK financial background: share prices and stock graph overlaid on an image of the Union Jack
Investing Articles

New to investing in the stock market? Here’s how to try to beat the Martin Lewis method!

Martin Lewis is now talking about stock market investing. Index funds are great, but going beyond them can yield amazing…

Read more »

Passive income text with pin graph chart on business table
Investing Articles

This superb passive income star now has a dividend yield of 10.4%!

This standout passive income gem now generates an annual dividend return higher than the ‘magic’ 10% figure, and consensus forecasts…

Read more »

Young woman working at modern office. Technical price graph and indicator, red and green candlestick chart and stock trading computer screen background.
Investing Articles

£5,000 invested in Tesco shares on 1 January 2025 is now worth…

Tesco shares proved a spectacular investment this year, rising 18.3% since New Year's Day. And the FTSE 100 stock isn't…

Read more »

This way, That way, The other way - pointing in different directions
Investing Articles

With 55% earnings growth forecast, here’s where Vodafone’s share price ‘should’ be trading…

Consensus forecasts point to 55% annual earnings growth to 2028. With a strategic shift ongoing, how undervalued is Vodafone’s share…

Read more »

A pastel colored growing graph with rising rocket.
Investing Articles

Here’s how I’m targeting £12,959 a year in my retirement from £20,000 in this ultra-high yielding FTSE 100 income share…

Analysts forecast this high-yield FTSE 100 income share will deliver rising dividends and capital gains, making it a powerful long-term…

Read more »

A senior man using hiking poles, on a hike on a coastal path along the coastline of Cornwall. He is looking away from the camera at the view.
Investing Articles

Is Diageo quietly turning into a top dividend share like British American Tobacco?

Smoking may be dying out but British American Tobacco remains a top dividend share. Harvey Jones wonders if ailing spirits…

Read more »

Young woman holding up three fingers
Investing Articles

Just released: our 3 top income-focused stocks to consider buying in December [PREMIUM PICKS]

Our goal here is to highlight some of our past recommendations that we think are of particular interest today, due…

Read more »

Person holding magnifying glass over important document, reading the small print
Investing Articles

Tesco’s share price: is boring brilliant?

Tesco delivers steady profits, dividends, and market share gains. So is its share price undervaluing the resilience of Britain’s biggest…

Read more »