Free UK investment projection
Junior ISA calculator: how much could it be worth?
See the value at 18, when it becomes theirs — and what it could grow to if they keep it invested.
Your plan
Growth compounds monthly at your chosen rate — 6% is a deliberately conservative default for a diversified global index fund. Contributions stop at 18; from there it's their money and their choice. Education, not financial advice — investments can go down as well as up.
Theirs at 18
£12,283
after 8 years of contributions — tax-free, and theirs to keep
£25,189
if they leave it invested until 30
Contributions stop at 18 — the growing doesn't
Child's age
At 18
£12,283
At 25
£18,674
At 30
£25,189
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Help them understand what they're building
Squids-In teaches your child how money grows, with short lessons and a friendly investing game. You stay in charge of the real thing.
Thinking longer term?
A Junior SIPP gets a 25% top-up on every contribution and grows until retirement. See what that could become — many families use both accounts together.
What the numbers are built on
01
Compound growth
A conservative 6% a year (typical for diversified index funds), compounded monthly — so growth earns growth.
02
Contributions stop at 18
A Junior ISA becomes theirs at 18. The projection keeps going, because leaving it invested gives it longer to grow.
03
Tax-free all the way
No income tax or capital gains tax inside a Junior ISA — and it rolls into an adult ISA at 18, still tax-free.
Frequently asked questions
How much can I pay into a Junior ISA each year?
The Junior ISA allowance is £9,000 per tax year (2026/27). Parents open the account, but anyone — grandparents, family, friends — can pay in, and all growth is completely tax-free.
What happens to a Junior ISA when my child turns 18?
At 18 the Junior ISA automatically becomes an adult ISA in your child's name, and the money is theirs. They can withdraw it — or keep it invested, where it keeps growing tax-free. Our calculator shows both moments: the value at 18, and what it could become if they leave it alone.
Is 6% a realistic growth rate?
Yes, 6% is a conservative estimate for a diversified global index fund over 10+ years. Global index funds have historically averaged more than this over long periods, before inflation — but past returns aren't a promise, so we use 6% to be careful.
What's the difference between a Junior ISA and a Junior SIPP?
The short version is access: a Junior ISA hands over at 18, a Junior SIPP is locked until pension age. Many families use both. Our full Junior ISA vs Junior SIPP guide walks through the limits, the tax relief and who each one suits. Read our full comparison.
Cash Junior ISA or stocks & shares Junior ISA?
This calculator models a stocks & shares Junior ISA, because over a whole childhood investment growth has historically beaten cash interest by a wide margin. Cash Junior ISAs suit short horizons; most children have the longest horizon there is.
Learn more about Junior ISAs
What is a Junior ISA?
Complete guide to Junior ISAs — how they work, contribution limits, and who can open one.
Read more →Junior ISA vs Junior SIPP
The two accounts compared — access ages, limits, tax treatment, and how families combine them.
Read more →One-off gift calculator
Birthday money or a grandparent’s lump sum — see what a single gift could become.
Read more →