Junior ISA Calculator: What Your Child Could Have at 18

By the Bureau of Wealth team Updated 15 September 2026

This calculator is general information, not financial advice. Check your own figures with the provider or a qualified adviser before acting on them.

Enter your child's age, what you save each month and any gifts from family to see what a Junior ISA could hold at 18, and what that is worth in today's money.

What this calculator assumes

Monthly saving and yearly gifts are paid in as 12 equal amounts at the end of each month, and stay the same every year until the child turns 18.
Growth or interest is a steady yearly rate after charges, converted to its monthly equivalent. Stocks and shares can fall as well as rise, and cash rates change, so real returns will differ.
No tax is deducted, because interest, growth and dividends inside a Junior ISA are tax-free.
The calculator warns you if the total paid in each year is over the £9,000 Junior ISA limit for 2026/27, but it still projects the full amount. It assumes the limit stays at £9,000.
The value in today's money divides the result by the inflation rate you enter for each year until 18. It does not model what the child does with the money afterwards.

Compound Interest Calculator
See how the same monthly saving grows over different periods and rates, which shows why starting early does so much of the work.
ISA Allowance Calculator 2026/27
If you would rather keep control of the money yourself, check how much of your own £20,000 ISA allowance is still free this tax year.

How the calculator works

The calculator works out how many years are left until your child turns 18. For each month it grows the balance at the monthly equivalent of your yearly rate, then adds that month's saving and a twelfth of the yearly gifts. At the end it shows the value at 18, how much was paid in, and how much came from growth.

Because a pound in 18 years will buy less than a pound today, it also shows the result in today's money, using the inflation rate you choose. That figure is a better guide to what the money might actually pay for.

A worked example

Say you save £100 a month from birth and assume 4% a year after charges and 2.5% inflation. After 18 years you have paid in £21,600, and the Junior ISA is worth about £31,335, so growth adds about £9,735. In today's money that is about £20,091.

If grandparents also give £200 a year, the value at 18 rises to about £36,557. If you start when your child is 5 instead of at birth, the same £100 a month grows to about £20,315 from £15,600 paid in.

What changes the result

Time and the growth rate make the biggest difference. At 2% a year, £100 a month from birth reaches about £25,929, against £31,335 at 4%. At 0%, you get back only the £21,600 you paid in, which is worth about £13,849 in today's money at 2.5% inflation.

There are two types of Junior ISA. A cash Junior ISA pays tax-free interest, and a stocks and shares Junior ISA has tax-free growth and dividends. The value of stocks and shares can go down as well as up, so use a lower rate if you want a cautious estimate.

The rules to know

In the 2026/27 tax year you can put up to £9,000 into a Junior ISA. That is £750 a month, and the calculator flags any plan that goes over it once gifts are added. The money belongs to the child. Parents or guardians with parental responsibility open and manage the account, the child can take control of it at 16, and they cannot withdraw the money until they turn 18.

That last point matters when you choose between a Junior ISA and saving in your own name. Once your child is 18, the money is theirs to use as they choose. If you would rather keep control, saving in your own ISA is an alternative, and the ISA allowance calculator shows how much of your own allowance you have left. A child cannot have a Junior ISA and a Child Trust Fund at the same time, but the trust fund can be transferred into a Junior ISA.

Frequently asked questions

How much can I put into a Junior ISA?

The limit is £9,000 for the 2026/27 tax year. The calculator adds your monthly saving and yearly gifts together and tells you if the total goes over.

Who owns the money in a Junior ISA?

The child does. A parent or guardian manages the account while the child is young, but the savings are the child's, and they can take control of the account at 16.

Can the money be taken out before 18?

Generally no. The child cannot withdraw the money until they turn 18. The one exception is if the child is terminally ill, when the registered contact can apply to HMRC to take money out early.

Should I choose a cash or stocks and shares Junior ISA?

Cash pays interest at a rate that can change. Stocks and shares can grow more over long periods but can also lose value. Run the calculator with a low and a higher rate to see the range.

My child has a Child Trust Fund. Can they have a Junior ISA too?

Not both at once. If you want a Junior ISA, you can ask the provider to transfer the Child Trust Fund into it.

Sources

Figures come from institutions millions of people rely on. How we keep calculators accurate.