The number of Britons with more than £1mn tucked away in individual savings accounts has surged by 52 per cent in a year, exposing the extraordinary wealth that can accumulate inside the UK’s tax-free savings system as ministers prepare to restrict the cash Isa allowance.
An estimated 7,730 people held Isa portfolios worth at least £1mn as of April 5 2024, up from 5,070 a year earlier, according to figures obtained from HM Revenue & Customs by money app Plum through a freedom of information request.
The increase added 2,660 people to the Isa millionaires club in just 12 months, highlighting how years of investment growth can turn tax-efficient savings into substantial fortunes.
The average Isa millionaire held a portfolio worth approximately £1.348mn, while the mean value of the 25 largest holdings was almost £11.93mn. Around 7,300 people had Isa balances between £1mn and £2mn, while about 60 held more than £4mn. This wealthiest group had average holdings of approximately £7.71mn.
The figures offer a striking illustration of the potential benefits of sheltering investments from tax. Unlike ordinary taxable investment accounts, Isas allow eligible returns and gains to accumulate without UK income tax or capital gains tax on the investments held within them.
But the numbers also underline the long-term advantage available to those with enough money to invest consistently and remain exposed to rising markets.
Will Bryant, director of wealth strategy at Plum, said the jump was revealing, arguing that Isa millionaires were not people who had simply saved their way to seven figures overnight.
“It’s the result of years of patient investing, where the growth on your growth starts doing the heavy lifting,” he said, pointing to the power of compounding and the performance of global markets, particularly US equities.
The figures should nevertheless be treated as estimates. HMRC cautioned that data supplied annually by Isa managers can contain errors or omissions, meaning the totals provide a guide rather than a definitive count.
The growing importance of Isas comes as the government prepares to change the rules. From April 2027, the annual cash Isa limit is due to fall from £20,000 to £12,000 for savers under 65, while the overall annual Isa allowance will remain at £20,000. Those aged 65 and over will retain the £20,000 cash Isa allowance.
The changes could encourage more savers to consider stocks and shares Isas, although investing exposes money to market risk and is not suitable for every household.
Bryant warned that many people might not understand the forthcoming changes. PensionBee vice-president of personal finance Maike Currie said Isas had become a valuable way for ordinary savers to build financial security, warning that restrictions risked making a straightforward product more complicated.
“Their beauty lies in their simplicity,” she said, adding that people did not need to become Isa millionaires to benefit.
The scale of money flowing into Isas suggests the accounts remain popular. HMRC figures show that adult Isa subscriptions reached £135.7bn in the 2024-25 tax year, an annual increase of £32.7bn. Cash Isa subscriptions rose by 37.5 per cent, accounting for £26.1bn of that increase, while subscriptions to stocks and shares Isas climbed by 19.7 per cent.
The challenge for policymakers is to preserve the appeal of tax-efficient saving while ensuring that changes do not discourage households from building financial resilience. The millionaire figures show what sustained investing can achieve over time — but they do not reveal how wealth is distributed among all Isa holders, or how many households lack the spare income to invest at all.
For most savers, the lesson is not that a million-pound Isa is within easy reach. It is that time, market performance and the ability to keep investing can make a significant difference — and that the rules governing tax-free savings matter long before a portfolio reaches seven figures.
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