How I’d invest £20k in a Stocks and Shares ISA today to make £1m

Rupert Hargreaves looks at the stocks and funds he’d pick for his ISA today with the goal of making £1m over the long term.

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.

The government’s decision to increase the annual Stocks and Shares ISA allowance to £20,000 was a boon for savers. That’s a substantial sum of money to be able to invest on a tax-free basis. Indeed, I believe if it’s invested correctly, this lump sum could help you become a millionaire investor.

The road to a million

I believe the best way to invest your money in a Stocks and Shares ISA is with funds and investment trusts.

Picking stocks is a tough business. Even the professionals regularly get it wrong. If you have £20,000 to work with, it might be better to avoid picking stocks altogether and pick collective investment vehicles instead. These will offer better diversification with much less time and effort required on your part.

According to my calculations, to be able to turn £20,000 into £1m, an investor will need to achieve an annual rate of return of 10% for 40 years. There are a variety of different investments you can use to hit this target.

For example, the FTSE 250 has produced an average annual return of around 9% for investors over the past decade. So you could buy the FTSE 250 and leave it at that. At an annual rate of 9%, I estimate it would take 45 years to turn £20k into a million.

However, I think a combination of funds and trusts would be a better investment strategy.

Equity income

For a start, I would use a low-cost income index tracker fund, such as Vanguard’s FTSE UK Equity Income Index Fund, to build the foundations of my portfolio.

Over the past decade, this fund has returned around 10% per annum by owning the UK Equity Index benchmark. It currently holds 128 of the UK’s top income stocks. I would allocate around a third of my portfolio to this investment.

Global growth

Another fund I would buy is a low-cost S&P 500 index tracker. The S&P 500 is an American index, but because the US equity market is by far the largest in the world, I think every investor should have some exposure to this leading stock market. It has returned around 9% per annum for the past 100 years and would be a perfect complement to the UK equity income investment in an ISA portfolio. This would be another one-third allocation.

Small-cap profits

My third and final pick would be a small-cap focused investment trust. According to fund rating agency Morningstar, over the past decade the Morningstar IT UK Smaller Companies index has produced an annualised return of 14.7%.

This market-beating performance is highly impressive, but the one downside of small-cap investing is volatility. That’s why I think the holding should be limited to just a third of a Stocks and Shares ISA portfolio.

The bottom line

So, that’s how I would invest £20,000 in a Stocks and Shares ISA today. As my figures above show, it looks as these three investments have the potential to achieve the double-digit returns required to create a fund worth £1m.

Rupert Hargreaves owns the Vanguard FTSE U.K. Equity Income Index Fund. 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

Sunrise over Earth
Investing Articles

Meet the ex-penny share up 109% that has topped Rolls-Royce and Nvidia in 2025

The share price of this investment trust has gone from pennies to above £1 over the past couple of years.…

Read more »

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

1 of the FTSE 100’s most reliable dividend stocks for me to buy now?

With most dividend stocks with 6.5% yields, there's a problem with the underlying business. But LondonMetric Property is a rare…

Read more »

Investing Articles

Is 2026 the year to consider buying oil stocks?

The time to buy cyclical stocks is when they're out of fashion with investors. And that looks to be the…

Read more »

ISA coins
Investing Articles

3 reasons I’m skipping a Cash ISA in 2026

Putting money into a Cash ISA can feel safe. But in 2026 and beyond, that comfort could come at a…

Read more »

US Stock

I asked ChatGPT if the Tesla share price could outperform Nvidia in 2026, with this result!

Jon Smith considers the performance of the Tesla share price against Nvidia stock and compares his view for next year…

Read more »

Investing Articles

Greggs: is this FTSE 250 stock about to crash again in 2026?

After this FTSE 250 stock crashed in 2025, our writer wonders if it will do the same in 2026. Or…

Read more »

Investing Articles

7%+ yields! Here are 3 major UK dividend share forecasts for 2026 and beyond

Mark Hartley checks forecasts and considers the long-term passive income potential of three of the UK's most popular dividend shares.

Read more »

Hand is turning a dice and changes the direction of an arrow symbolizing that the value of an ETF (Exchange Traded Fund) is going up (or vice versa)
Investing Articles

2 top ETFs to consider for an ISA in 2026

Here are two very different ETFs -- one set to ride the global robotics boom, the other offering a juicy…

Read more »