Stocks and shares ISA explained
An ISA isn't an investment — it's a wrapper that removes UK tax on whatever you put inside it. Here's the 2026/27 allowance, the cash ISA change arriving in April 2027, and the rules people trip over.
What it actually is
A stocks and shares ISA is not an investment. It is a wrapper you put investments inside, and the wrapper does one job: it removes UK tax on what happens within it. No capital gains tax on growth, no further tax on dividends, and nothing to declare on a tax return.
Inside it you can hold shares, funds, investment trusts, ETFs, corporate and government bonds. The same investment held inside and outside the wrapper behaves identically, except one is taxed and the other isn't.
The allowance
The ISA allowance for the 2026/27 tax year is £20,000 per person, running from 6 April 2026 to 5 April 2027. That is the total across all ISA types — cash, stocks and shares, innovative finance and lifetime — not £20,000 each. The Lifetime ISA has its own £4,000 sub-limit that counts within the overall figure, and the Junior ISA allowance is £9,000.
Unused allowance does not roll forward. Anything not used by 5 April is gone permanently. Since April 2024 you have been able to pay into more than one ISA of the same type in a tax year, provided the combined total stays within the allowance.
What the tax saving is actually worth
On small balances, not much — the annual capital gains exemption and dividend allowance already cover modest amounts held outside a wrapper. The value compounds with size and time. A portfolio built up over twenty years inside an ISA can be sold entirely with no capital gains tax at all, which is the point at which the wrapper stops being a marginal benefit and becomes a large one.
The counter-consideration is that the allowance is use-it-or-lose-it. Every April that passes without using it removes capacity you cannot get back, which is why people front-load contributions even when the immediate saving looks small.
Practical points that catch people out
Transfers don't use the allowance
Moving an existing ISA between providers, or between ISA types, doesn't count against your £20,000. Only new money does. Always use the provider's transfer process rather than withdrawing and re-depositing, which would consume allowance.
Losses aren't relievable
Because gains inside an ISA are untaxed, losses inside one can't be offset against gains elsewhere. A symmetrical consequence people rarely think about in advance.
Platform fees still apply
The wrapper is free of tax, not free of charges. Compare the platform's annual fee structure — percentage-based fees suit small balances, flat fees suit large ones.
US dividends are still taxed at source
An ISA shelters you from UK tax, not from foreign withholding tax. US dividends typically suffer withholding regardless, though completing a W-8BEN with your broker usually reduces the rate.
Flexible versus non-flexible
Some ISAs let you withdraw and replace money in the same tax year without it counting twice against the allowance. Many don't. Check before withdrawing.
Cash ISA or stocks and shares ISA?
Different jobs. Cash protects the nominal amount and pays interest — appropriate for money you'll need within a few years. A stocks and shares ISA can fall in value and is appropriate for money you won't need for at least five years, in exchange for the possibility of growth ahead of inflation over long periods. Neither is a better product; they answer different questions about when you need the money.
What goes inside it is the separate and larger decision — a broad index fund, individual companies you've valued, or some combination.
Deciding what to hold inside it
Oak Growth estimates intrinsic value and margin of safety across roughly 1,000 companies in nine markets, scored on moat, management, economics and value.
Explore Oak GrowthCommon questions
What is the ISA allowance for 2026/27?
£20,000 per person for the tax year running from 6 April 2026 to 5 April 2027. That total covers all ISA types combined rather than each one separately, with the Lifetime ISA capped at £4,000 within it and the Junior ISA allowance set at £9,000.
Is a stocks and shares ISA worth it?
The wrapper removes UK capital gains and dividend tax on everything inside it. On small balances the saving is limited because allowances outside a wrapper already cover modest amounts, but it compounds with size and time, and unused allowance is lost permanently each 5 April.
What is changing with cash ISAs in 2027?
From 6 April 2027, the annual cash ISA limit for under-65s falls from £20,000 to £12,000, with the remaining £8,000 of the allowance available for investment-type ISAs. The overall £20,000 allowance is unchanged, the stocks and shares limit stays at £20,000, and those aged 65 and over are unaffected.
Does transferring an ISA use my allowance?
No. Moving an existing ISA between providers or between ISA types doesn't count against the annual limit — only new contributions do. Use the provider's formal transfer process, because withdrawing and re-depositing would consume allowance.
Also see: Is £1,000 enough to start investing? → · What is an ETF? → · What if you invest £1,000 a month? →