The number of Isa millionaires who invest with stockbroker AJ Bell has jumped 74 per cent in a year, it has revealed.

In the year between December 2024 and December 2025, AJ Bell saw the number of Isa millionaires on its platform balloon - although it wouldn't give exact numbers on how many people are now in this exclusive club.

Isas have exploded in popularity in recent years and there are now at least 5,100 Isa millionaires in the UK - although it is likely this number has grown, as the most up-to-date data takes us to April 2023.

Almost £500billion is stashed by investors in stocks and shares Isas and recent data suggests around 2.5million people now fully use the £20,000 annual limit.

AJ Bell has revealed what its most successful investors have in common, from how old they were when they became an Isa millionaire to how many investments they hold.  

What do they invest in?

Something all Isa millionaires have in common is that they are far likely to hold individual shares than the everyday investor.

Funds and ETFs are less popular with Isa millionaires. This is because many are experienced investors and expert stock pickers who have conviction in their own ability to choose winning stocks, AJ Bell says.

Isa millionaires on AJ Bell's platform hold, on average, 83 per cent of their portfolios in shares, including investment trusts, with most of the rest in funds. 

By comparison, this figure is 58 per cent in stocks across other Isa holders.

Oil giant Shell is the single most popular stock among the biggest Isa investors, taking the top spot in the list of most popular holdings for the last two years running.

Isa millionaires are also drawn to blue chip names on the UK stock market, including household names which have been around for decades like banking group Lloyds and life insurer Legal & General. 

Income-seeking investors also tend to look to FTSE100 companies for the high yields on offer. 

Investment trusts also have a place in Isa millionaires portfolios, according to AJ Bell. 

The most popular investment trusts held by Isa millionaires are Scottish Mortgage, Alliance Witan and JPMorgan Global Growth & Income. 

'A preference to back mature, established businesses over start-ups might reflect the typical older age of an Isa millionaire,' says Dan Coatsworth, head of markets at AJ Bell.

Isa millionaires hold, on average, 23 different positions within their portfolios, although this differs dramatically depending on the investor. 

Some hold over 150 different investments, while a handful have just a single investment in their portfolio.

How old are they?

It can take decades of dedication to become an Isa millionaire, reflected by the fact that the majority of Isa millionaires investing with AJ Bell are in their 60s and 70s. 

The average age of an Isa millionaire with AJ Bell is 70.

Dan adds: 'With an average age of 70, many stocks and shares Isa super investors will have built their portfolio over decades and may have originally held investments in PEPs (Personal Equity Plans) before the introduction of Isas over a quarter of a century ago.'

But this does not mean no younger investors have hit the £1million milestone.

Some successful Isa investors managed to get to their first Isa million before turning 40. While the youngest Isa millionaire on AJ Bell's platform is just 33 years old.

The most successful Isa investors have racked up their second Isa million before they turned 50.

Mr Coatsworth says: 'It's worth pointing out those with a sizeable portfolio at such a young age often tend to pursue a high conviction strategy focused on specific stocks, which won't be for everyone.'

On the other end of the scale, some of AJ Bell's Isa millionaires are in their 90s. The oldest Isa millionaire investing with AJ Bell is a centenarian of 100 years old.