2027 ISA Rules Set New £12,000 Cash ISA Limit

The driest documents sometimes matter most. A Treasury regulation made on 10 September 2026, laid before the House of Commons on 14 September 2026 and due to take effect on 6 April 2027 quietly rewrites part of how ISAs work, especially if you are under 65 and use cash savings as your main shelter from tax. Read past the legal wording and three changes stand out. The new rules create a £12,000 annual limit on cash ISA subscriptions for people aged 64 or under at the end of the tax year, bring money market funds more clearly into the ISA rulebook, and change the tax treatment of interest earned on cash sitting inside some non-cash ISAs.

Before we get lost in regulation numbers, it helps to reset what an ISA is for. In simple terms, an ISA is a tax wrapper. You put savings or investments inside it, and the returns are usually protected from the normal tax bill. Cash ISAs are built around deposits. Stocks and shares ISAs are for investments. Innovative Finance ISAs cover certain alternative finance products. **What this means:** the government is not scrapping ISAs. It is changing the rules inside them. According to the note attached to the legislation on legislation.gov.uk, the main focus is cash limits, money market funds, and the way some interest is taxed and reported.

The biggest headline change is the new cash ISA ceiling. From 6 April 2027, if you are 64 or under at the end of the tax year, the total you can subscribe across your cash ISA accounts in that year will be £12,000. That wording matters. It is an aggregate cap, so it follows you across providers and across multiple cash ISA accounts. It is also age-tested at the end of the tax year, not on the day you pay the money in. If you are 65 or over at the end of the year, this new cash-only ceiling does not apply.

This does not mean younger savers are banned from using cash ISAs, and it does not mean every ISA contribution above £12,000 suddenly breaks the rules. What the regulation does is add a separate cash-account limit alongside the wider ISA subscription rules that already sit in the background. The legal drafting then updates the repair rules and the flexible-account rules so providers can deal with cases where someone breaches either limit. **What it means for you:** if you are under 65 and you like spreading emergency savings, house-deposit money or other short-term cash across several ISA accounts, you will need to track the combined total much more carefully from the 2027/28 tax year onwards. The cap is about the overall amount, not the number of accounts.

The next change looks technical but is actually quite teachable. The regulations add a formal definition of a money market fund and then let these funds count as qualifying ISA investments. Money market funds are usually sold as cash-like investment funds. They tend to hold very short-term, lower-risk debt rather than ordinary shares, which is why many savers see them as somewhere between cash and investing. From April 2027, money market funds can sit inside a cash ISA, and they can also appear inside a stocks and shares ISA. But there is a catch in the stocks and shares rules. The plain-English reading is that a stocks and shares ISA cannot be made up entirely of money market funds as its non-cash holdings. You can think of that as a line between a temporary cash-like holding and a full investment account.

The tax change is where many readers will need to slow down. New regulation 22A says that when interest, or an alternative finance return, is paid on cash deposits held inside a stocks and shares ISA or an Innovative Finance ISA, that return will no longer get normal ISA tax relief. Instead, the account manager must pay HMRC a flat-rate charge on that interest or return, using the savings basic rate for that year. The saver does not get a repayment. In practice, this draws a sharper line between cash left sitting on a platform as a deposit and money placed into qualifying investments such as a fund.

There is also an age split in the transfer rules. The legislation says current-year and previous-years' subscriptions in a stocks and shares ISA or Innovative Finance ISA may be transferred into a cash ISA only if the account holder is 65 or over at the end of the year. That is a strong policy choice. Younger adults are still being allowed to use the ISA system, but the rules seem designed to make it harder to keep shifting large tax-sheltered balances back into plain cash. Older savers are treated differently. Whether you see that as sensible caution or unnecessary state steering, it is clearly written into the text.

Some of the other amendments are housekeeping, but they matter because they make the main changes enforceable. Application forms will need to reflect the new cash limit. Reporting rules will need to capture money market fund holdings and any tax charge due under regulation 22A. The account manager, not the individual saver, is the person who must account to HMRC for those sums. The regulations also strip out some obsolete wording, including old references tied to the age an account holder needs to be to open an account. That kind of editing rarely makes headlines, but it helps show that this is not one isolated tweak. It is a full tidy-up around a new set of boundaries inside the ISA system.

This is one of those tax measures that arrives dressed as administration but changes behaviour in the real world. The Treasury's own note says the instrument makes related changes to subscriptions, transfers, tax liabilities and reporting. Put simply, the rules are trying to separate cash, cash-like funds and investment ISAs more clearly than before. **What to watch now:** if you are a saver, the date to remember is 6 April 2027. If you are a teacher, adviser or student of current affairs, the useful question is not just 'what changed?' but 'where will people get caught out?'. The likely pressure points are under-65 cash savers, people treating platform cash like a tax-free waiting room, and anyone who assumes a money market fund is always the same thing as a bank deposit.