The **cash ISA limit cut to £12,000** takes effect on 6 April 2027 and applies to everyone under the age of 65. The overall ISA allowance does not change: you can still shelter £20,000 a year. What changes is where that £20,000 is allowed to sit. Only £12,000 of it may go into a cash ISA, and the remaining £8,000 must go into a stocks and shares ISA, an innovative finance ISA or a Lifetime ISA — or not be sheltered at all. Savers aged 65 and over keep the full £20,000 cash entitlement.
HMRC published the draft Individual Savings Account (Amendment) Regulations 2026 for technical consultation in July 2026, with comments closing at 11:59pm on 2 August 2026. The draft goes further than the headline number, adding a 22% charge on interest paid on cash held inside a stocks and shares ISA, a ban on transferring from a stocks and shares ISA into a cash ISA, and a rule that a portfolio made up entirely of cash-like assets stops qualifying at all. For US citizens and Green Card holders living in Britain there is a separate point that the mainstream coverage will not make: the tax break being reduced was never available to you in the first place.
What the cash ISA limit cut to £12,000 actually does
The mechanics are simpler than the commentary suggests. Today an adult can subscribe up to £20,000 across their ISAs in a tax year and can choose to put all of it into cash. From 6 April 2027, an under-65 saver faces a sub-limit: a maximum of £12,000 of that £20,000 can be new cash ISA subscriptions. The £8,000 balance remains available, but only through a stocks and shares ISA, an innovative finance ISA or a Lifetime ISA within its own £4,000 annual cap.
Money already inside a cash ISA is untouched. The lower limit bites on new subscriptions only, so a saver with £200,000 accumulated across previous years' cash ISAs keeps every penny of that shelter and continues to receive the interest free of UK tax. Nothing is clawed back, nothing has to be moved, and there is no requirement to convert existing holdings into investments. This is the single most misunderstood point in the coverage, and the one that causes the most unnecessary panic.
The 22% charge on cash held inside a stocks and shares ISA
The Treasury anticipated the obvious workaround. If under-65s can only put £12,000 into a cash ISA, the natural response is to open a stocks and shares ISA, subscribe the other £8,000, and simply leave it in the account's cash facility earning interest — a cash ISA in all but name. The draft regulations shut that down with a flat-rate 22% charge on any interest or alternative finance return paid on cash held inside a stocks and shares ISA or innovative finance ISA. The charge is collected from the ISA manager, who pays it to HMRC, rather than being assessed on the investor directly.
The rate is deliberately blunt. It sits above the 20% basic rate, which removes the incentive for a basic-rate saver to game the rules, and below the 40% and 45% rates, which means a higher or additional-rate taxpayer with cash sitting idle in a stocks and shares ISA is still marginally better off than holding the same cash in an ordinary savings account. It is a friction charge, not a penalty — designed to make parking cash inside an investment wrapper unattractive rather than impossible.
The transfer ban and the cash-like asset rule
Two further anti-circumvention rules complete the package. First, transfers from a stocks and shares ISA or an innovative finance ISA into a cash ISA will not be permitted for account holders under 65. Transfers in the other direction — from cash into stocks and shares — remain allowed, as does the ability of a saver who turns 65 to move freely again. The asymmetry is intentional: the government wants the flow of money to run from deposits into investment, not back.
Second, an ISA portfolio made up entirely of cash-like assets becomes a non-qualifying investment. The draft defines the category narrowly: money market funds are treated as cash-like, while shares, bonds, investment trusts and exchange-traded funds are not. A stocks and shares ISA holding 100% money market funds therefore falls foul of the rule, whereas one holding a short-dated gilt fund does not. Anyone whose strategy involves sitting in a money market fund for extended periods should read the final regulations carefully when they are laid.
What to do before 5 April 2027
There is a genuine, time-limited planning window here, and it is one of the rare cases where the obvious action is also the correct one. The current £20,000 cash entitlement survives for the 2026/27 tax year in full. An under-65 saver who wants to maximise permanently sheltered cash has until 5 April 2027 to subscribe up to £20,000 into a cash ISA under the old rules — and that money stays sheltered indefinitely once it is inside.
For a couple, that is £40,000 of cash moved permanently out of the UK tax net before the limit falls, against £24,000 in the following year. If you were going to hold the cash anyway, using this year's full allowance costs nothing and locks in eight thousand pounds of extra shelter per person that will not be available again. That is the whole of the planning point, and it does not require any change to your investment strategy.
- Subscribe up to £20,000 to a cash ISA before 5 April 2027 if you hold the cash and are under 65 — the shelter is permanent.
- Existing cash ISA balances are unaffected; there is no need to move or restructure anything already held.
- From 6 April 2027, plan on £12,000 cash plus £8,000 into a stocks and shares, innovative finance or Lifetime ISA.
- Do not park the £8,000 as cash inside a stocks and shares ISA — the 22% charge is designed to remove that option.
- If you are 65 or over, or will turn 65 in the relevant tax year, nothing changes: the full £20,000 cash entitlement continues.
Why this matters less if you hold a US passport
Here is where the British commentary stops being useful. An ISA is a creature of UK law. The United States does not recognise it, has no treaty provision protecting it, and taxes its citizens on worldwide income regardless of residence. To the IRS, a cash ISA is an ordinary foreign bank account and a stocks and shares ISA is an ordinary foreign brokerage account. The wrapper is invisible.
That means interest credited to your cash ISA is taxable on your Form 1040 as ordinary income in the year it arises, at your marginal US rate, whether or not you withdraw it. The UK gives you a tax-free return; the US taxes the same return. If you are a US person, the £8,000 of cash shelter being withdrawn in 2027 was, from a whole-of-life tax perspective, worth considerably less to you than it was to your British colleagues — because half of the benefit was already being taxed away on the other side of the Atlantic.
The stocks and shares ISA problem is much worse than the cash one
The reform pushes savers towards stocks and shares ISAs. For an American in the UK that is precisely the wrong direction, and it is worth understanding why before you follow the crowd. Most UK funds and investment trusts held inside a stocks and shares ISA are Passive Foreign Investment Companies under US law. The PFIC regime applies a punitive default calculation — the excess distribution method — that spreads gains back over your holding period, taxes them at the highest ordinary rate for each year, and adds a non-deductible interest charge on top. It also requires Form 8621, often one per fund per year.
The practical result is that the £8,000 the government wants you to redirect from cash into a stocks and shares ISA is the most US-tax-toxic place you could put it. We set out the full mechanics in PFIC rules and UK ISAs. For most US persons in Britain, the sensible response to the 2027 reform is not to move £8,000 into funds inside an ISA but to hold US-domiciled investments in a taxable account, or to use a UK pension, which the treaty does protect.
Does the 22% ISA manager charge create a US credit?
This is the technical question a well-advised American will ask, and the answer matters. The 22% charge is levied on the ISA manager in respect of interest paid on cash within a stocks and shares ISA. It is not an income tax assessed on you personally. A foreign levy generally has to be an income tax, and has to be your legal liability, before it becomes creditable against US tax under the foreign tax credit rules.
A charge collected from the account provider sits awkwardly against both tests. The prudent working assumption, until the final regulations and any HMRC guidance clarify the point, is that the 22% will reduce the interest credited to your account without generating a corresponding US foreign tax credit — an economic cost with no US offset. That is a strong practical argument for a US person to avoid holding meaningful cash inside a stocks and shares ISA at all from April 2027, quite apart from the PFIC issue.
What happens to cash held outside an ISA
If the reform pushes £8,000 a year of your cash out of the shelter, the question becomes how that interest is taxed in ordinary savings. For 2026/27, the Personal Savings Allowance gives basic-rate taxpayers £1,000 of interest tax-free, higher-rate taxpayers £500, and additional-rate taxpayers nothing at all. Above that, interest is taxed at your marginal rate — 20%, 40% or 45%.
There is also the starting rate for savings, a £5,000 band taxed at 0% that sits above the £12,570 personal allowance, giving a threshold of £17,570. It is withdrawn pound for pound as non-savings income rises, so it is genuinely useful only to those with low earned income — a non-working spouse, someone between roles, or a retiree living on capital. You can model the outcome with our UK savings interest tax calculator, and size the effect of the new limit itself with the cash ISA limit calculator.
The reporting obligations nobody mentions
Whatever you decide about the wrapper, the US reporting follows the account. A cash ISA is a foreign financial account for FBAR purposes, so it counts towards the $10,000 aggregate high-balance threshold that triggers FinCEN Form 114. A stocks and shares ISA counts too, and each fund inside it is potentially a separate PFIC on Form 8621. Depending on your totals, Form 8938 under FATCA may also apply, with thresholds that are considerably higher for taxpayers living abroad than for those in the States.
None of this is discretionary and none of it depends on whether the account produced income. The IRS guidance on FBAR filing requirements sets out the aggregate test, and the GOV.UK draft ISA regulations consultation documents the UK side of the change. If you have been holding ISAs for years without reporting them, that is a fixable problem — see FBAR versus FATCA for UK expats for how the two regimes differ.
How the 2027 change interacts with the rest of the UK's tax rises
The ISA reform does not arrive in isolation. Dividend rates rose from April 2026, capital gains rates have been climbing, and Business Asset Disposal Relief moved to 18% for disposals on or after 6 April 2026. Read together, the direction of travel is a steadily narrower set of shelters for UK-resident wealth, with the ISA the last major one available without professional structuring.
For an American in Britain the cumulative effect is different again, because each UK rise generally increases the foreign tax credit available against your US liability rather than adding to your total burden. Higher UK rates on dividends, covered in the UK dividend tax rise from April 2026, often mean more creditable tax rather than more tax overall. The ISA is the exception: it is the one place where a UK tax break produces no US benefit, so its reduction costs you proportionately less.
Common mistakes we expect to see in 2027
The first is panic-moving existing cash ISA balances, on the mistaken belief that the £12,000 limit applies to holdings rather than subscriptions. It does not. The second is opening a stocks and shares ISA purely to absorb the extra £8,000 in cash, which the 22% charge exists to punish. The third, specific to US persons, is buying UK-domiciled funds inside that new stocks and shares ISA and discovering the PFIC consequences three years later when the accountant asks what is inside the wrapper.
The fourth is a timing error: assuming the change applies from April 2026. It does not. The 2026/27 tax year runs under the current rules, and the full £20,000 cash entitlement is available until 5 April 2027. Acting a year early achieves nothing; acting a year late loses the window permanently.
- Do not move existing cash ISA balances — the limit applies to new subscriptions only.
- Do not park cash in a stocks and shares ISA to absorb the £8,000 — the 22% charge removes the benefit.
- US persons: do not buy UK funds inside an ISA without understanding PFIC and Form 8621 first.
- Do not assume the change starts in April 2026 — it starts on 6 April 2027.
- Do not assume the ISA shelters anything on your US return. It does not, and never has.
How TaxStone approaches ISAs for US persons
At TaxStone we start from the position that an ISA is a UK-only benefit and should be sized to the UK-only part of your position. For a dual filer, that usually means using the cash ISA to the extent it is genuinely useful, keeping investments out of the wrapper unless they are individual shares or US-domiciled holdings, and pushing long-term savings towards the UK pension route that the US–UK treaty actually protects.
We also look at the sequencing. If you expect to leave the UK, or to renounce, or to move back to the States, the right ISA strategy today is different from the right strategy for someone staying permanently. If you would like that mapped for your own circumstances, contact us or book a free consultation and we will run both systems side by side rather than one at a time: /get-started.
The short version
From 6 April 2027, under-65s can subscribe a maximum of £12,000 a year to a cash ISA, out of an unchanged £20,000 overall allowance. Savers aged 65 and over keep the full £20,000 in cash. Existing balances are unaffected. A 22% charge applies to interest on cash held in a stocks and shares or innovative finance ISA, transfers from those wrappers into a cash ISA are blocked for under-65s, and an all-cash-like portfolio ceases to qualify. The draft regulations were consulted on until 2 August 2026.
The action point for everyone is the same: if you are under 65 and hold the cash, use the full £20,000 cash allowance before 5 April 2027, because that shelter is permanent and will not be available again. The action point for Americans in the UK is different: the benefit you are losing was largely notional on your US return anyway, and the wrapper the government is steering you towards is the one most likely to create a PFIC problem. Plan the US side first and the UK side second.
