Grandparents love putting money into a Junior ISA. What far fewer of them clock is that the moment the child turns 18, the account stops being anyone else's business — no strings, no staged release, no way for a parent to say "actually, let's wait until you've finished university." Every penny becomes the child's, in cash or in shares, to spend on a car, a gap year, or a deposit on a flat. For some families that is exactly the point. For others, it is a surprise they only discover when the birthday has already passed.
Junior ISAs (JISAs) were introduced in November 2011 to replace Child Trust Funds, and they remain the most widely used tax-free wrapper for children's savings in the UK. Any UK-resident child under 18 who doesn't already hold a Child Trust Fund can have one opened by a parent or legal guardian, who then acts as the "registered contact" — the person who manages the account, even though the money legally belongs to the child from day one. Grandparents, aunts, uncles, family friends, anyone at all can pay into an existing JISA. They just can't be the one who opens it.
The £9,000 Allowance, and Who's Actually Using It
The Junior ISA allowance sits at £9,000 per tax year, split however you like between a Cash JISA and a Stocks & Shares JISA, and it has stayed at that level since April 2020 — no inflation uplift, no political noise, just a flat figure carried forward year after year. Compare that with the adult ISA allowance of £20,000 and it looks generous relative to what most families can actually afford to put aside for a child. HMRC's savings statistics have consistently shown that only a small minority of eligible children have a JISA subscription in any given tax year, and average contributions run closer to four figures than to the full £9,000 ceiling. Most parents are putting in birthday and Christmas money, not maxing out the allowance on day one of the tax year.
Unused allowance doesn't roll over. If you pay in £2,000 this tax year and nothing next year, that unused £7,000 is simply gone — there's no carry-forward mechanism the way there sometimes is with pension annual allowances. Set up a standing order the month the account opens rather than relying on remembering to top it up before the 5 April deadline; £150 a month gets you to £1,800 a year without anyone having to think about it again.
Cash JISA or Stocks & Shares JISA
A Cash JISA behaves exactly like a normal savings account, just tax-free and locked to the child until 18. Rates from providers such as Nationwide, Halifax and Coventry Building Society have typically sat in the 3.5%–4.5% range through 2026, and the money is protected up to £85,000 under the Financial Services Compensation Scheme. That security comes at a cost: over a horizon of ten, fifteen, eighteen years, cash returns rarely outpace inflation by much, and a newborn's JISA has exactly that kind of horizon built in.
A Stocks & Shares JISA holds funds, investment trusts or individual shares inside the same tax-free wrapper, through providers like Hargreaves Lansdown, AJ Bell, Fidelity, interactive investor or Moneybox. Over an 18-year window, a globally diversified equity fund has historically outperformed cash by a wide margin, even accounting for the 2008 and 2020 drawdowns along the way — and for a young child's account, that time horizon is precisely the argument in favour of taking the risk. Choose the Stocks & Shares route for a child under ten. There is no realistic case for parking a newborn's ISA entirely in cash for the next eighteen years and watching inflation quietly erode it.
The Junior SIPP: A Pension for a Five-Year-Old
Fewer parents know that a Junior Self-Invested Personal Pension exists, and even fewer use one, but the tax mechanics are genuinely striking. A parent or guardian can pay in up to £2,880 net per tax year, and HMRC automatically tops it up with 20% basic-rate tax relief — turning that £2,880 into £3,600 inside the pension, even though the child has never paid a penny of income tax. Do that every year from birth to 18, and the contributions alone total £64,800, before a single pound of investment growth is added on top.
The catch is access. Junior SIPP money is locked until the normal minimum pension age, currently 55 and rising to 57 from 2028, with the government having signalled it intends to keep that age roughly ten years below the State Pension age going forward — meaning a child born today should assume they won't see the money until somewhere in their late fifties or early sixties. That is either the entire point (a genuinely un-raidable pot compounding for six decades) or a complete non-starter, depending on whether you're trying to fund a first car or a first pension.
The 18th Birthday Problem
Here's the part almost nobody plans for properly. On the child's 18th birthday, a Junior ISA converts automatically into an adult ISA in their name, and full control passes to them — the parent's registered-contact role simply ends. There is no vesting schedule, no phased handover, no way to say the money releases at 21 or 25 instead. A responsible, university-bound 18-year-old might use a £30,000 JISA sensibly. A different 18-year-old might not, and there is genuinely nothing a parent can do about it once the birthday arrives — no clause in the account terms, no override, no cooling-off period.
Families who want more control sometimes split the strategy: fund the JISA up to a level they're comfortable handing over unconditionally, and put anything beyond that into a bare trust or a parental GIA (General Investment Account) instead, where the parent retains legal control for longer even though the underlying asset is still the child's for tax purposes. It's more paperwork, and a GIA loses the JISA's tax-free wrapper, but for a family expecting to build a genuinely large pot, that trade-off is often worth making deliberately rather than discovering it by accident on the child's 18th birthday.
JISA, Junior SIPP, or Both
For most families, the Junior ISA should be the default and the Junior SIPP the add-on, not the other way round. A JISA gives the family flexibility — university costs, a first car, a deposit, whatever comes up at 18 — while a SIPP locks the money away for decades with no early-access route at all. Open both if the budget stretches to it: £150 a month into the JISA and £50 a month into the SIPP is a realistic split for many households, and the SIPP's 20% top-up means that £50 becomes £62.50 the moment it lands, without the child lifting a finger.
Skip the SIPP entirely if you're not confident you'll keep contributing for the long haul — a Junior SIPP opened and then abandoned after two years still locks that money away until the child's late fifties, for a relatively modest sum. The JISA has no such penalty for irregular contributions; pause it, restart it, top it up erratically, and none of that changes when the child gets access.
Opening One: What Actually Happens
Opening a JISA online with any of the major providers takes under fifteen minutes if you have the child's National Insurance number (issued automatically before their 16th birthday, but a temporary reference works before that) and your own ID. Transfers between providers are free by law, and cash-to-stocks-and-shares transfers within the JISA wrapper don't count against the annual allowance — only new money paid in does.
- Check whether the child already has a dormant Child Trust Fund, since roughly £1.7 billion sits in unclaimed CTFs across the UK and it needs transferring in before a JISA can be opened alongside it.
- Decide the Cash vs Stocks & Shares split before the first payment, not after — moving existing contributions later is possible but adds friction.
- Set the registered contact correctly; it can only be a parent or legal guardian, and changing it later requires paperwork most providers process in writing rather than online.
The account doesn't need six-monthly rebalancing or active management to be worth opening. A single low-cost global tracker fund, left alone for eighteen years, does most of the work — and the biggest single decision a parent makes is simply starting the standing order this month rather than next.