Junior ISA calculator (JISA)
See how a Junior ISA grows tax-free until a child turns 18, and how much of the £9,000 annual Junior ISA allowance a given contribution uses.
Balance at 18 (in 13 years)
£52,894
£3,000 a year is 33% of the £9,000 annual Junior ISA allowance.
Where the balance comes from
Total contributed
£40,000
Tax-free interest earned
£12,894
Balance over time
Move across the chart to inspect any point.
Assumes a fixed interest/growth rate and consistent monthly contributions, compounding monthly, staying within the annual Junior ISA allowance each tax year. Not financial advice.
How a Junior ISA works
A Junior ISA is opened by a parent or guardian for a child under 18, but anyone — grandparents, other family, friends — can contribute towards the £9,000 annual allowance, which is entirely separate from the adult £20,000 ISA allowance. Growth and interest inside the account are tax-free, just like an adult ISA.
The money is locked away until the child turns 18 — at 16, the child can take over managing the account, but still can't withdraw anything until their 18th birthday, when it automatically converts into a regular adult ISA fully under their own control.
Frequently asked questions
Related calculators
Lifetime ISA
Saving for your own retirement or first home? See the Lifetime ISA's 25% bonus.
Cash ISA
This is the child's own separate allowance — see the adult ISA rules here.
Compound interest
The same tax-free growth math, for savings without a JISA's age lock.