Turning 18: What Happens to a Junior ISA in 2026/27

What actually happens on the birthday

A Junior ISA is a tax-free wrapper that anyone (parents, grandparents, the child themselves once working) can pay into up to the annual JISA limit, but which the child cannot touch until 18. On the 18th birthday there is no transfer, no new account number in most cases, and no tax event — the same wrapper simply becomes an adult ISA of the equivalent type (cash JISA → cash ISA; Stocks & Shares JISA → Stocks & Shares ISA).

From that point:

• The account holder is the only person with access — parents who were named as registered contact lose that role.
• The money can be withdrawn, spent, or moved to another provider at any time.
• The adult £20,000 annual ISA allowance applies from the start of that tax year, separate from what's already in the account.

The decision points at 18

1. Leave it invested and keep contributing

If the JISA was a Stocks & Shares JISA and the saver doesn't need the cash immediately, the simplest option is to do nothing and keep contributing toward a longer-term goal (house deposit, general wealth building). Growth inside the ISA stays entirely tax-free — no income tax on dividends or interest, no Capital Gains Tax on withdrawal.

2. Split toward a Lifetime ISA for a house deposit

From 18, a saver can open a Lifetime ISA (LISA) and get a 25% government bonus on up to £4,000 paid in per tax year — worth up to £1,000 a year — provided the money is eventually used for a first home (up to £450,000) or left until 60. Moving JISA money into a LISA doesn't earn a bonus retroactively; only new contributions from 18 onward qualify.

3. Spend some, save some

There's no rule against spending JISA money — it belongs to the saver outright. Many 18-year-olds use part of it for university costs, a first car, or a deposit on a rental flat, and preserve the rest. Splitting a converted JISA between "spend now" and "leave invested" is a reasonable middle path rather than an all-or-nothing choice.

Why the £20,000 allowance timing matters

Because the adult allowance applies from the tax year containing the 18th birthday (not from the exact birthday date), someone who turns 18 in, say, November 2026 gets the full £20,000 2026/27 allowance for the whole tax year — they don't need to wait until April.

What if the JISA provider doesn't offer a good adult ISA rate

JISA providers sometimes roll converted accounts onto an uncompetitive "legacy" adult ISA rate. It's worth transferring to a better-rate cash ISA or a low-cost Stocks & Shares ISA platform using the formal ISA transfer process (never withdraw-and-reopen, which loses the tax-free status of that year's contribution).

Sources

• gov.uk: Junior Individual Savings Accounts (ISA)
• gov.uk: Individual Savings Accounts (ISA)
• gov.uk: Lifetime ISA
• MoneyHelper: Junior ISAs explained