Junior ISA projector
The Junior ISA annual limit for 2026/27 is £9,000, which works out at £750 a month, under gov.uk's rules for Junior Individual Savings Accounts. This calculator projects what a Junior ISA could be worth by age 18 from a monthly contribution and an assumed growth rate, and compares a cautious cash assumption against a stocks and shares one.
That is over the £9,000 a year limit, so the monthly amount has been capped at £750.
How does the Junior ISA projection work?
The tool grows the starting balance and each monthly payment at the growth rate chosen, compounding month by month until the child turns 18.
It applies the £9,000 a year Junior ISA limit set out on gov.uk automatically, so a monthly figure that would exceed it is capped at £750.
The result is an estimate of the pot the child would hold on their 18th birthday, when the account becomes theirs and converts to an adult ISA, under gov.uk's Junior Individual Savings Accounts rules.
The cash and stocks figures beside the main number use fixed assumptions of 3% and 6% a year so the spread can be compared. Real returns are never this smooth. Cash is steadier but tends to trail inflation, while a stocks and shares JISA can grow more over a long stretch and can also fall, so the gap shown is a guide to the trade-off rather than a forecast.
What would a Junior ISA be worth in a worked example?
Starting at age 3 with nothing saved and paying in £100 a month at 5% a year means £18,000 is contributed over 15 years. Steady growth lifts the pot to about £26,482 by age 18, so roughly £8,482 of that is growth rather than money paid in. At a cautious 3% the same payments would reach about £22,624, and at 6% about £28,691, which shows how much a few percentage points of growth matter across a childhood.
Common questions
How much can I pay into a Junior ISA?
The Junior ISA limit is £9,000 a tax year, which is £750 a month. That allowance covers a cash JISA and a stocks and shares JISA together, so paying into both still shares the same £9,000.
When can the money be taken out?
The child cannot access the money until they turn 18, and neither can you once it is paid in. At 18 the account becomes theirs and an adult ISA, and they decide what happens to it. That lock is the point of the account, but it is worth being sure before you commit.
Cash or stocks and shares Junior ISA?
Over a long run to age 18, a stocks and shares JISA has usually grown faster than cash, but it can fall in value and is not guaranteed. Cash is steadier but often loses ground to inflation. The comparison here shows the gap a few percentage points of growth make over many years.
Who can pay into a Junior ISA?
A parent or guardian opens it, but anyone can contribute, so grandparents and family can add money too. Everything paid in still counts towards the single £9,000 yearly limit for that child.
Does a Junior ISA affect my own ISA allowance?
No. The £9,000 Junior ISA limit is separate from your own £20,000 adult ISA allowance, so paying into a child’s JISA does not reduce what you can save yourself.
How does the Junior ISA projection work?
The projector compounds the starting balance and each monthly payment at the growth rate entered, month by month, until the child turns 18. It applies the £9,000 a year Junior ISA limit automatically, capping the monthly figure at £750 where a higher contribution would exceed it. The figure shown is the pot the child would receive on their 18th birthday.
What would a Junior ISA be worth in a worked example?
Starting at age 3 with nothing saved and paying £100 a month at a 5% assumed growth rate gives a projected pot of about £26,482 by age 18, of which roughly £8,482 is growth rather than money paid in. At a cautious 3% a year the same payments would reach about £22,624, and at 6% about £28,691. These are illustrative figures based on steady, unbroken growth, and an actual return would vary from year to year.
Sources & Rate Verification
Rates verified against official statutory guidance on 6 September 2026.