Junior ISA Calculator

Every number on this page assumes the money stays invested until the child turns 18. What happens next is worth knowing before you commit a single pound: the account converts automatically into an adult ISA, and from that day the child has complete legal ownership and control. You don't get a say in whether they use it for university, a deposit, a car, or a holiday with friends. Parental access ends the moment they turn 18, by law, with no mechanism to attach conditions.

This isn't a loophole or an edge case; it's the entire design of a Junior ISA. If you want money whose use you can influence for longer, a Junior ISA is the wrong vehicle for that specific goal. If you're comfortable with genuinely unconditional giving, a Junior ISA does exactly what it says on the tin: it becomes theirs, fully, at 18, no strings attached.

The larger number on this page, the projected value in future pounds, is the one that's easiest to get excited about, and the least useful for actually planning anything. £30,000 in eighteen years' time doesn't buy what £30,000 buys today. Prices have historically roughly doubled over a period that long, so a headline figure like that needs to be mentally halved to understand what it's really worth by the time your child can spend it.

The inflation-adjusted figure does that halving for you, using a standard 2% assumption, the same rate financial regulators use for their own illustrations, and the Bank of England's own inflation target. It answers the actual question most parents are asking, which isn't “what will the account statement say” but “what will this actually be worth to my child when they need it.” Treat the two figures as answering different questions: the nominal figure is what the provider will show; the real figure is what it can buy.

As a concrete example: £1,000 in today plus £100 a month, growing at 5% for the full 18 years, projects to roughly £36,900 in future pounds, but only around £25,900 once adjusted back to today's prices. Both numbers are “the projection”; only one of them tells you what that money will actually feel like to spend.

Every projection on this page runs on a single assumed annual growth rate, held constant for the entire period. Real investment returns don't work that way. They vary from year to year, sometimes sharply, and for a stocks-and-shares JISA in particular, some years will be negative. A market fall isn't a remote possibility over an 18-year window; it's something that has happened multiple times in most 18-year periods on record.

The default rates on this page (5% for stocks-and-shares, 3% for cash) are standard illustrative assumptions used across the industry, not predictions specific to your child's account or any promise from us. Changing the number changes the projection, but it doesn't change reality. The actual outcome will be higher or lower than any single-rate projection can show, and won't be smooth from year to year even if the average roughly matches over time. Use this tool to understand the shape of compounding, not to bank on an exact figure eighteen years from now.

The current Junior ISA allowance is £9,000 a year, combined across a cash JISA and a stocks-and-shares JISA if the child has both, not £9,000 for each. A child can hold at most one of each type, ever. Unlike adult ISAs, which since April 2024 can be split across multiple accounts of the same type, Junior ISAs were specifically excluded from that change, so this one-of-each-type limit isn't going away.

Only a parent or legal guardian can open the account, but anyone can pay into it once it exists: grandparents, other family, friends all count toward the same £9,000 cap, so it's worth checking with everyone contributing rather than assuming your own payments are the only ones being counted. At 16, the child can take over managing the account themselves, though they still can't withdraw anything until 18. That's the one meaningful milestone between opening the account and it becoming fully theirs to control.

Choosing between the two account types comes down largely to time horizon. Cash JISAs don't fall in value, which matters if the child is close to 18 and you'd be uncomfortable seeing the balance drop right before they need it. Stocks-and-shares JISAs can fall in value, sometimes sharply, but have historically tended to outpace cash and inflation over long periods, which is more relevant the younger the child is, since there's more time for a bad year or two to be offset by better ones. There's no rule against holding both at once, split however suits your circumstances, as long as combined contributions stay within the single £9,000 allowance.