Project Junior ISA pot at age 18.
Pot at age 18
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A tax-free pot the child controls at 18
A Junior ISA is the most efficient way to build a meaningful sum for a child in the UK. You can pay in up to £9,000 each tax year, every penny of growth and income is free of UK income tax and capital gains tax, and the money is locked away until the child turns 18, when the account automatically becomes an adult ISA in their name. The lock is the point. Because no one can dip in for 18 years, the pot gets the full benefit of long-run compounding. This calculator projects where regular contributions land by the child's eighteenth birthday.
The power of starting at age three
Take the defaults: £3,000 a year from age three, with an assumed 6 percent annual return. That is 15 years of contributions. The tool treats each year's £3,000 as paid at the start of the year, so it compounds for a full extra year, and the projected pot at 18 is about £74,018. You will have put in £45,000 of your own money, and growth adds roughly £29,018 on top. Almost two-fifths of the final figure is investment return you never contributed, which is what an 18-year runway buys you.
Cash or stocks, and the £9,000 ceiling
The £9,000 limit is per child per tax year and is shared across both types of Junior ISA, so a child can hold a Cash Junior ISA and a Stocks and Shares Junior ISA at once, but the combined contributions cannot exceed £9,000. Over an 18-year horizon a Stocks and Shares Junior ISA almost always wins, because equity returns have historically outpaced cash and inflation by a wide margin, and the long lock-in rides out short-term volatility. A Cash Junior ISA only makes sense if the child is already a teenager and you want certainty over the last couple of years. Note that the Junior ISA allowance is entirely separate from your own £20,000 adult ISA allowance, so funding a child's account does not eat into your own tax-free room.
Who should open one, and what to watch
This tool is for parents, grandparents, and guardians planning ahead for university costs, a first car, or a house deposit. Anyone can pay into a child's Junior ISA once it is open, though only a person with parental responsibility can open it and manage it. A practical tip worth knowing: gifts into a Junior ISA reduce your own estate and can use your annual inheritance tax gifting exemptions, which makes grandparent contributions doubly efficient. The honest caveat that surprises many families is control. At 16 the child can take over managing the account, and at 18 the money is legally theirs to spend as they wish. If you want a say over how an 18-year-old uses a five-figure sum, a Junior ISA may not be the right wrapper, and a trust or a pension started for the child could suit better. Junior ISA rules are identical across the whole UK.
Can I withdraw money before the child turns 18?
No, other than in narrow circumstances such as the child becoming terminally ill or, sadly, dying. The account is designed to be untouchable until 18, which is exactly what gives it the long compounding advantage, but it also means you should only commit money you are sure you will not need back.
What happens to the account at 18?
On the child's eighteenth birthday the Junior ISA automatically rolls into a standard adult ISA in their name, keeping its tax-free status, and the full balance becomes theirs to access or reinvest. It does not count against the £9,000 junior limit any longer, and from that point the adult £20,000 annual ISA allowance applies to any new contributions they make.