What happens to a Junior ISA at 18?

A Junior ISA does not end when the child grows up. It changes hands. On the child's 18th birthday the account automatically turns into an adult ISA, and the money inside it becomes theirs to control¹. Nothing is sold, nothing is cashed in and nothing is lost: the tax-free wrapper simply moves from a child's account to an adult one.

The practical effect is that the person who has been paying in, usually a parent or grandparent, loses any say over the money. Until that birthday, withdrawals are not allowed at all¹. From the 18th birthday, the account holder can take the money out, leave it invested, add to it within the annual ISA allowance, or move it to another provider².

There is a halfway stage worth knowing about. A child can take over management of their own Junior ISA from age 16, even though they still cannot touch the money until 18³. Providers write to the account holder before the change, so nobody should be caught out by it.

A Junior ISA becomes an adult ISA automatically at 18

The conversion is not something anyone applies for. Government guidance states plainly that Junior ISAs "automatically turn into an adult ISA when the child turns 18"¹. Providers describe the same event in their own terms: the account "automatically matures into an adult ISA"⁷, it "automatically becomes a regular ISA on the child's 18th birthday"⁸, and it "automatically rolls over into a normal adult ISA"⁹.

Because it happens automatically, there is no gap in which the money sits outside a tax wrapper. The account holder does not need to open anything, sign anything or make a choice on the day. The account they already have simply becomes an adult ISA in their name.

What does change is who is in charge. Before 18, a parent or guardian manages the account while the child is under 16, and from 16 the child can choose to manage it themselves³. At 18 the account holder has full control, and the money is theirs¹⁰.

Cash or stocks and shares: which type it turns into

A Junior ISA is opened as either a cash account or a stocks and shares account, and it converts into the matching adult version¹¹. A junior cash ISA becomes an adult cash ISA, and a junior stocks and shares ISA becomes an adult stocks and shares ISA.

Providers are consistent about this. Coventry Building Society says a junior cash ISA "will convert to an adult cash ISA" and calls the result a Matured Junior ISA¹². Interactive Investor says that on the date the child turns 18 "the JISA turns into a Stocks & Shares ISA"⁷. Moneybox describes its account maturing "into a standard Stocks & Shares ISA which they can access and manage"¹⁴. Royal Bank of Scotland says its Junior ISA "will change to an adult Stocks and Shares ISA"¹⁵.

The type matters because it decides what the money is doing when the account holder takes it over. Cash stays as cash. Investments stay invested, with the same funds or shares unless the new adult decides otherwise. Nothing is automatically switched from one to the other at 18.

Who controls the account from the 18th birthday

Control passes in two stages, and the first one often surprises families. A parent or guardian manages a Junior ISA while the child is under 16, but once the child reaches 16 they can choose to manage their own account³. NS&I puts it the same way: a parent or guardian can manage the ISA for a child while they are under 16, and once the child reaches 16 they can manage it themselves¹⁶. The legislation behind this treats a contract entered into by a child aged 16 or over as if they had been 18¹⁷.

Managing is not the same as spending. Even at 16, the money stays locked. As one official guide puts it, "you can control your account from 16, but you'll only be able to take out the money after you're 18"¹⁸.

At 18 the second stage arrives and control is complete. The account holder can give instructions, change investments, move provider or withdraw. Vanguard states that from that point "the ISA belongs to them, and they'll have full control over the account"¹⁰.

Can parents stop a child taking the money out at 18?

No. There is no mechanism for it. Withdrawals are barred until the child turns 18, and that is the whole of the protection¹. Once the birthday passes, the account is an adult ISA and the individual decides what happens to the money².

This is worth being clear-eyed about before the money builds up. A Junior ISA is a long-term savings account designed to build a nest egg, and the rules deliberately hand it over at 18 rather than at some later age¹⁶. A parent who wants the money used for university, a house deposit or anything else has no legal way to insist.

The one thing an adult can control is what they pay in. Contributions are voluntary, and stopping them is the only lever available. Once the money is in, the child's claim on it at 18 is absolute.

Withdrawing the money or keeping it invested

At 18 the account holder has a genuine choice, and doing nothing is one of the options. They can leave the money where it is, take some of it, take all of it, or carry on investing²¹. NFU Mutual describes the choice as continuing with the investment by converting the Junior ISA to an adult ISA, or taking out some or all of the money²².

Leaving it alone is often the least disruptive route. The account is already an adult ISA, so it keeps its tax-free status and can stay invested without any paperwork. The account holder can then add to it within the annual ISA allowance like any other adult.

Taking money out is straightforward once the account has converted. There is no tax to pay on withdrawals from an ISA, and no penalty for taking money out of the converted account. That is different from a Lifetime ISA, where withdrawals before 60 for anything other than a first home normally carry a charge.

Transferring the converted ISA to another provider

Once the account has become an adult ISA, it can be moved. The transfer rules allow a cash ISA or a stocks and shares ISA to move into any other type of ISA, with the exception of Junior ISAs²⁴. So an adult ISA that started life as a Junior ISA can go to a different provider, or into a different ISA type altogether.

The mechanics matter. Transfers between providers must go through the official transfer process rather than being withdrawn and paid back in²⁵. Withdrawing the money and reinvesting it elsewhere would use up the annual allowance and could leave the money outside a tax wrapper in the meantime.

Some providers ask for paperwork. Mansfield Building Society notes that funds can be transferred into an adult ISA at that point, but the account holder has to complete an ISA application²⁰. NS&I transfers the whole balance and asks the customer to contact the new provider to arrange it¹⁶.

Adult ISA eligibility starts at 18

Turning 18 opens up the adult ISA market properly. Adult cash ISAs are available to children from the age of 16, and eligible children can hold both a Junior cash ISA and an adult cash ISA at the same time²⁶. But children are only eligible for a full adult ISA when they turn 18²⁷.

That means a 16 or 17 year old can already hold a cash ISA in their own name alongside their Junior ISA, and can continue to open and save into a Junior ISA as well²⁸. From 18, the converted Junior ISA sits alongside whatever else they open, and the annual ISA allowance applies across everything they hold.

The account holder can also open a new adult ISA in the same year as the conversion. There is no rule preventing someone from holding the converted account and a freshly opened one. What they cannot do is pay more than the annual allowance across all of them combined.

What the provider does, and when

Providers are required to make contact before the change, and the timing varies. TSB writes at least 30 days before the 18th birthday to the Junior ISA account holder and to the registered contact if that is a different person⁴. NS&I contacts the person who looks after the Junior ISA about a month before the transfer into an adult cash ISA⁵.

The letter usually explains what the account is becoming, what the options are and whether any paperwork is needed. For most accounts, no action is required at all. Where the money is moving to a different provider, or where the provider wants a fresh application, the letter will say so.

If no letter arrives, the conversion still happens. The account becomes an adult ISA on the birthday regardless of whether the paperwork has been read.

Where the protection sits

The tax-free status of the money does not depend on the conversion being handled well. A Junior ISA becomes an adult ISA, and the adult ISA rules apply from that point: no tax on interest, dividends or capital gains within the wrapper.

If something goes wrong with the account, the usual protections apply. ISA providers are regulated, and complaints can go to the Financial Ombudsman Service if a provider does not resolve them. Cash held with a bank or building society is covered by the Financial Services Compensation Scheme up to its limit, and investments are covered under the scheme's investment rules, which work differently from the cash limit.

The protection that stops applying at 18 is the one that kept the money out of the child's hands. That protection is time-limited by design, and the 18th birthday is when it ends.