Junior ISA (JISA) Calculator
Estimate how much of a financial head start you can give your child. See how regular contributions to a tax-free Junior ISA grow over 18 years.
Last updated: May 2026
Max £750/mo (£9k/yr limit)
Fund Value at Age 18
You Contributed
£22,600
Tax-Free Growth
+£19,266
This entire amount will be legally transferred to your child when they turn 18. It is completely tax-free and will not count towards their adult ISA allowance for that year.
Reviewed by Anjali Mehta
•Personal Finance AnalystA seasoned financial journalist and analyst. Anjali focuses on making complex financial data accessible and ensuring our tools provide practical, real-world value to users. All mathematical models and regulatory data points have been verified for the current 2026 fiscal period.
What is a Junior ISA?
A Junior Individual Savings Account (JISA) is a tax-free savings and investment wrapper for children living in the UK.
Parents or guardians can open the account, and anyone (including grandparents and friends) can contribute to it, up to an annual limit of £9,000 per tax year. The money is locked away until the child's 18th birthday, at which point it legally belongs to them and automatically converts into a standard adult ISA.
How to use this calculator
- 1Child's Age — Enter your child's current age. The money must stay in the account until they turn 18.
- 2Plan Contributions — Input your monthly deposit. The maximum is £750/month to stay within the £9k annual limit.
- 3Estimate Return Rate — If you use a Cash JISA, use ~4%. If using a Stocks & Shares JISA, use 6-8%.
Formula & example
The 18-Year Compound Growth Rule
Example: Investing £100/month from birth to age 18 at a 7% return.
- Total Contributed: £21,600
- Tax-Free Growth: ~£20,000
- Fund at 18: ~£41,600 (A massive university fund or house deposit!)
Benefits
No Tax, Ever
No Capital Gains Tax and no Income Tax on the returns, forever.
Long-Term Compounding
Because the money is locked for up to 18 years, compound interest has maximum time to work its magic.
Separate Allowance
JISA contributions do NOT count towards the parents' own £20,000 adult ISA limit.
Use cases
University Fund
Ensuring your child graduates debt-free.
First House Deposit
Giving your child the ultimate head start on the property ladder at age 18.
Frequently asked questions
Can I take the money back?+
No. Once money is put into a Junior ISA, it belongs to the child. You cannot withdraw it, even in emergencies (except in cases of terminal illness).
What happens when they turn 18?+
The JISA automatically converts into a normal adult ISA. The child gets full legal control and can choose to withdraw the cash or keep it invested.
Can they have a Cash JISA and a Stocks & Shares JISA?+
Yes, a child can have one of each type, as long as the combined contributions don't exceed the £9,000 annual limit.