Junior ISA Calculator
Tax-free growth for a child to 18 — JISA allowance, who controls the money and the 18th-birthday handover.
Formula
Disclaimer: Assumes constant returns; market investments fluctuate and tax rules change — verify current-year limits. Educational math only, not financial or tax advice.
Need junior isa calculator results fast? Skip the spreadsheet and get a clear, defensible answer in one step — free, private and instant, recalculating live as you change any input.
About Junior ISA Calculator
A Junior ISA gives a child the one asset adults can't buy: decades of runway. £200 a month from age 3 at 7% hands over roughly £63,000 at 18 — and if left untouched in the adult ISA it becomes at 18, that same pot compounds toward £480,000 by age 47 without another penny added. The allowance (around £9,000 per tax year) is generous enough that few families cap it. Structure: anyone can contribute (grandparents love JISAs — gifts out of income can also be IHT-efficient), but the money is irrevocably the CHILD's — parents manage investments until 16, the child can take control of decisions at 16, and at 18 the money is legally theirs to spend on index funds or a motorcycle. That handover risk is the JISA's only real drawback; financial education is the hedge, and it starts years before 18. Investment choice matters more here than anywhere: an 18-year horizon is the textbook case for equity index funds over cash — cash JISAs, still nearly half the market, have historically cost children five figures of outcome versus equity at these durations. Fee drag compounds against the same long runway; cheap global trackers are the default answer.
How to use Junior ISA Calculator
- 1Enter Monthly contribution, Expected annual return (%), Years until 18 (years) into the Junior ISA Calculator.
- 2The result is computed automatically using Monthly compounding inside the tax-free wrapper until the child turns 18, when the JISA becomes their adult ISA — there is no button to press; it updates live as you type.
- 3Change any input to model a different scenario, then use “Copy result link” to share the exact numbers.
Why use Junior ISA Calculator?
- ✓Computes junior isa calculator instantly with the correct formula — no spreadsheet needed
- ✓100% free and unlimited, with no sign-up, login or paywall
- ✓Runs entirely in your browser, so the figures you enter are never uploaded or stored
- ✓Shows the formula, a live worked example and references so you can defend the number
Frequently asked questions
Who can open and pay into a Junior ISA?+
A parent/guardian opens it; ANYONE can then contribute — grandparents, godparents, family friends — within the child's annual allowance. One cash + one stocks JISA may exist simultaneously (allowance shared). Children with Child Trust Funds must transfer the CTF in rather than opening a JISA alongside.
Can we get the money back if we need it?+
No — contributions are gifts to the child, locked until 18 except in terminal-illness/death cases. That's a feature (the money survives family financial storms) and a planning constraint: keep the family emergency fund OUTSIDE JISAs. If access-flexibility matters more than the child's legal ownership, a parent's own ISA earmarked mentally for the child is the alternative.
What ACTUALLY happens at 18?+
The JISA converts automatically into an adult ISA in the child's name with full control and the standard adult allowance opening on top. No tax event, no forms for the child beyond ID. The real event is behavioral — an 18-year-old with £60,000. Families that involve teens in the account's decisions from ~14 report better outcomes than those who reveal it as a surprise.
Cash JISA ya stocks JISA — bachhe ke liye kya sahi?+
15+ saal ke horizon par equity index funds ka case overwhelming hai: cash 2-4% deta hai, equity historically ~7%+ — 15 saal me yeh farak pot ko lagbhag dugna kar deta hai. Cash JISA sirf tab jab 18 ke kareeb ho (2-3 saal) aur paisa university fees jaisi pakki zaroorat ke liye ho. Default: sasta global tracker, set-and-forget.
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