At the start of the 2023/24 tax year, 5,070 people held ISA portfolios worth £1 million or more, according to an HMRC Freedom of Information request. A new Freedom of Information request by Rathbones for This is Money shows it is likely 17,600 investors will have reached ISA millionaire status by the end of the current tax year, which ends in two weeks. New analysis by Rathbones suggests the number of ISA millionaires will have risen to 17,600 by April 2026, assuming 8% annual investment growth and full use of the £20,000 ISA allowance each year. Angela Smith, senior investment director at Rathbones, said, "Our analysis of the data suggests the number of ISA millionaires is likely to have risen significantly over a relatively short period, even on modest assumptions."
Historically, the number of ISA millionaires has at least doubled every three years since 2016, and more than trebled during periods when MSCI World returns exceeded 15%, according to Rathbones. Global equities have delivered annualized returns of 17.4% since April 2023, the firm noted. Smith added, "This means many more investors are now benefiting from tax-free growth, income and dividends on seven-figure portfolios." The specific factors driving this rapid growth beyond general investment returns, such as economic conditions or policy changes, remain unclear.
Our analysis of the data suggests the number of ISA millionaires is likely to have risen significantly over a relatively short period, even on modest assumptions.
Even if savers stopped contributing to their ISAs altogether after April 2023, an 8% annual return could still lift the number of ISA millionaires from 5,070 to around 7,100 by April 2024, nearly 9,510 by April 2025, and almost 13,100 by April 2026, according to Rathbones analysis. Smith emphasized, "Our experience with clients shows that the not-so-secret ingredients behind building an ISA millionaire portfolio are patience, time, consistently using allowances, and avoiding interruptions to the power of compounding." How this growth rate compares to other investment or savings account millionaires, such as pension accounts, over the same period is not detailed in the analysis.
In Sweden, a similar trend is unfolding with Investment Savings Accounts (ISKs). In 2023, nearly 3.8 million Swedes had an ISK, according to reports. Last year, a historic milestone was passed: for the first time, more than 4 million Swedes, exactly 4,218,556 people, have an ISK, as reported. The number of Swedes with an ISK increased by over 450,000 people in just two years, according to data. Demographic trends characterizing these new account holders, such as age or income level, are not specified.
This means many more investors are now benefiting from tax-free growth, income and dividends on seven-figure portfolios.
An Investment Savings Account is a so-called standard-taxed account, meaning you do not need to tax each time you sell your assets at a profit, unlike a regular fund account, according to sources. Starting in January 2026, the first 300,000 kronor in an ISK is projected to be completely tax-free, which would be a doubling compared to 2025 when the tax-free allowance was 150,000 kronor, as reported. According to TV4 Nyheterna, Christina Sahlberg, a savings economist at Skandia, described the ISK as simple because it avoids declaration requirements. Potential risks for investors relying heavily on these accounts, given assumptions about continuous growth and tax benefits, are not addressed in the reports.
Today, over 211,000 children under 16 years old have their own Investment Savings Account in Sweden, according to reports. According to TV4 Nyheterna, Christina Sahlberg described that parents can open ISKs in their own names to save for children or in the children's names to take advantage of the tax-free allowance per person, but noted it is legally the children's money in the latter case. Future changes in tax policies or investment returns could impact projected growth in both countries, though such effects are not quantified. Smith concluded, "Even after investment gains, £1 million is no longer what it used to be."
Our experience with clients shows that the not-so-secret ingredients behind building an ISA millionaire portfolio are patience, time, consistently using allowances, and avoiding interruptions to the power of compounding.
Even after investment gains, £1 million is no longer what it used to be.
It's simple. You avoid declaring. It's a simple way you tax on.
You can either have an ISK that you open yourself in your own name and save for your children. Then you have full control over this money and can give it to your children at any time. Or you can open an ISK in the children's names. Then you can take advantage of this tax-free allowance because it applies per person. But then it's very important to remember that it is the children's money legally.
The absolute most important thing is not to save for your children. It is to teach your children about money.