A Junior ISA has one unusual advantage over almost every other financial decision a parent makes: time.
Money can go in when a child is born and remains there until they turn 18. There are very few circumstances in which it can come out sooner. Yet HMRC says that, in 2023-24, more than a third of the £1.8 billion paid into Junior ISAs went into cash.
That’s £655 million being put aside for children – often for many years – without being invested.
Martin Lewis recently made the obvious case in a MoneySavingExpert email. If money is genuinely being locked away until 18, he argued, investing rather than saving deserves serious consideration. Junior ISAs, as he put it, can “hit the sweet spot for when to invest”.
In my view, what’s even more interesting is why so many parents still end up doing something else.
A long horizon with an odd set of incentives
Parents – or legal guardians – can put up to £9,000 into a Junior ISA each tax year. The money grows free of UK Income Tax and Capital Gains Tax and the child normally can’t withdraw it until 18. So far, so sensible.
But then you try to choose one.
MoneySavingExpert’s best-buy tables illustrate a peculiarity of the market. At the time of writing, the highest-paying Junior Cash ISAs include Leek Building Society at 3.85%, Skipton at 3.8%, Stafford at 3.76% and Coventry at 3.75% – all requiring post or a branch. The leading digital option, NS&I, pays 3.7%.
The investment market looks rather different. Hargreaves Lansdown, IG and Fidelity currently charge no platform fee for a Junior ISA, whereas Vanguard charges 0.15% a year. Managed products can cost 0.6-0.7% before fund charges.
Now, suppose a family uses the full £9,000 allowance each year for eighteen years. Assuming a flat 6% gross investment return, the difference between a platform costing 0.15% a year and one costing 0.7% can run to around £16,000 over the period.
By comparison, the difference between earning 3.85% and 3.7% on cash is worth roughly £4,000 on the same pattern of contributions.
While these are just illustrations and the value of investments may rise or fall, the useful point is one of scale. Parents can spend a lot of effort optimising decisions that matter less than the one sitting immediately above them: whether an 18-year pot should be held in cash or invested in the first place.
The cash habit is hard to break
According to HMRC, there were 1.37 million Junior ISAs subscribed to in 2023-24 – up from 1.25 million the year before. Contributions reached £1.8 billion, with cash accounting for 36.4% of the total (down from 42.2%).
That decline is encouraging, but £655 million is a lot of money to put into cash accounts designed for children.
Of course, there are perfectly reasonable reasons to do it. While some parents don’t want market risk attached to their children’s savings, others may be dealing with an older teenager whose 18th birthday is approaching, so moving some investments into cash can make sense. No investment rule should be applied mechanically.
An 18-year investment horizon can make market volatility easier to accommodate, but it doesn’t make the decision psychologically easier.
The financial industry hasn’t always helped either. Choice is often presented as a virtue in investing, but it can become a burden surprisingly quickly. Several thousand funds may be excellent for someone who knows precisely what they want. For a parent opening their first investment account at eleven o’clock at night after putting a child to bed, however, abundance can look rather like admin.
Why we built the new Prosper Junior ISA differently
All of these considerations have influenced the Junior Stocks & Shares ISA we’ve just launched at Prosper.
We wanted to build around the things that matter most over a long horizon: keeping costs low, making investing straightforward and avoiding incentives that reward people for leaving money idle or choosing a more expensive route.
There’s also something personal about launching this product now, with my own children already teenagers.
While I can’t go back and open the Prosper Junior ISA I would’ve wanted for them when they were born, I can make it available to the parents and legal guardians starting that journey today.
From one parent to another, that’s the point of it.
This article is for informational purposes only and does not constitute personal financial advice. If you are unsure whether an investment is right for you, please seek regulated financial advice.
Sources:
- MoneySavingExpert – Junior Cash ISA guide / best buys
- MoneySavingExpert – Junior Stocks & Shares ISA guide
- HMRC – Annual Savings Statistics, September 2025 commentary
- HMRC – full Annual Savings Statistics 2025 release and underlying tables
- GOV.UK – April 2027 ISA reforms
- GOV.UK – Find a lost Child Trust Fund