Patient investing has driven the number of ISA millionaires – those with £1 million or more held in their ISAs – to a record high of 7,730 in the latest tax year.
The figures, revealed in a Freedom of Information (FOI) request sent to HMRC by savings and investment app Plum, mark an increase of more than 50% in the number of ISA millionaires in the 2023/24 tax year, compared to 5,070 in the tax year prior.
The average ISA millionaire now has a pot worth £1,348,000, virtually the same as the average in the 2022/23 tax year despite over 5,000 more individuals becoming ISA millionaires.
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“A jump of more than 50% in a single year is really telling,” said Will Bryant, director of wealth strategy at Plum. “These aren’t people who suddenly saved their way to £1 million. It’s the result of years of patient investing, where the growth on your growth starts doing the heavy lifting. That’s the bit people underestimate.”
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The number of ISA multi-millionaires has also increased, with 320 individuals sitting on ISA pots worth between £2 million and £3 million, 40 with pots between £3 million and £4 million, and 60 with accounts worth over £4 million.
Among those 40 with pots worth more than £4 million, the average account value was £7,708,000. This figure balloons to just under £12 million when looking at only the top 25 ISA investors in the UK.
As any money held in an ISA is shielded from capital gains tax and dividend tax, returns from these portfolios will be protected from a hefty tax bill. For example, a portfolio of £1 million which grew by 15% – the average return from the S&P 500 index over the last 10 years – will have brought tax-free returns of £150,000.
Bryant added: “These investors didn’t reach millionaires’ row by selling every time things got scary. They’ve sat through financial crises, Covid, rising interest rates and tariff worries, all of it.
“Staying put is harder than it sounds, but it’s time in the market, not trying to time the market, that works. And this data is proof of that.”
Are there any cash ISA millionaires?
While it is theoretically possible for someone who put their full £20,000 ISA allowance into cash each year since 1999 to have become an ISA millionaire, it is incredibly unlikely.
The vast majority of ISA millionaires joined the club by putting their ISA contributions into the stock market.
A separate FOI request sent to HMRC by Murphy Wealth in 2025 found that in the 2021/22 tax year, not a single ISA millionaire managed to reach the figure through cash ISA holdings alone.
The request found that 94% of the UK’s ISA millionaires got there exclusively through stocks and shares ISAs while the remaining 6% held money in a combination of cash and stocks and shares ISAs.
How can you become an ISA millionaire?
While joining the ISA millionaire’s club may seem a distant dream, diligent and patient investors could get there sooner than you may think.
Data from Plum shows that someone starting from scratch today and putting their full £20,000 ISA allowance into a stocks and shares ISA could reasonably expect to become an ISA millionaire in around 22 years, assuming annualised returns of 7% after fees.
Any investors who want to reach £1 million in their ISA should remember that patience is key.
Charlene Young, head of technical at AJ Bell: “ISA millionaires paint a great picture of what can happen when investors combine time, regular contributions, patience and perhaps a bit of good fortune.”
She said that those who want to build up £1 million in their ISAs will need to adopt a ‘get rich slow’ mindset and start as early as possible.
“There will be younger investors with a high-risk appetite who have achieved huge returns, but ordinary investors are normally best served by a diversified portfolio held for the long term.”
As for what you should invest in, Young says there isn’t a single route to becoming an ISA millionaire.
“Analysis of AJ Bell’s ISA millionaire investors has shown that shares and [investment] trusts are especially popular, but there are plenty using funds too. The important thing is to invest in what you feel comfortable with and understand the level of risk you are taking in return for the potential reward.”
