How stocks and shares ISAs work

A stocks and shares ISA isn't an investment. It's a box you put investments in. The box has one job: to keep the taxman's hands off whatever happens inside it.

That's worth knowing up front, because "is a stocks and shares ISA a good idea?" is really two questions. Is investing right for you? And if it is, do you want to pay tax on it? The second one has an easy answer.

What goes in the box

GOV.UK lists what a stocks and shares ISA can hold: shares in companies, unit trusts and investment funds, corporate bonds, government bonds and long-term asset funds.

In practice, most people hold funds, which spread money across lots of companies at once. You open the ISA with a provider, put money in, and then choose what to buy with it. Money sitting in the ISA that you haven't invested yet is just cash waiting to be used.

The tax it saves

Inside an ISA, you don't pay tax on income or capital gains from investments. That covers the two ways investments make money.

Dividends

Dividends are the share of profits companies pay out to shareholders. Outside an ISA, you get a £500 dividend allowance each year. Above that, dividends are taxed at 10.75% for basic-rate taxpayers, 35.75% at the higher rate and 39.35% at the additional rate. GOV.UK is clear that you don't pay tax on dividends from shares in an ISA.

Gains

If you sell an investment for more than you paid, the profit is a capital gain. Outside an ISA, the tax-free allowance for gains is £3,000 a year. Shares you've put into an ISA are on GOV.UK's list of things you don't pay Capital Gains Tax on.

£500 and £3,000 sound like plenty when you're starting out. They stop sounding like plenty once a pot has grown for twenty years. The ISA means you never have to do that maths, and never have to fill in a tax return for it.

How much you can put in

In the 2026 to 2027 tax year, the most you can save in ISAs is £20,000. That's across all your ISAs together, and you can put it in one account or split it across several. The tax year runs from 6 April to 5 April.

Use it or lose it. Your ISAs don't close when the tax year ends, but there's no carry-forward of allowance you didn't use.

From 6 April 2027, a change is coming for cash. People under 65 will be able to put no more than £12,000 a year into cash ISAs. The overall £20,000 limit stays, so the rest can still go into a stocks and shares ISA. People aged 65 and over keep a £20,000 cash limit. The same GOV.UK document says there will be restrictions on moving money from stocks and shares ISAs into cash ISAs, so the lower limit can't be dodged with a transfer.

You must be 18 or over and UK resident to open one, with some exceptions for Crown servants and the armed forces. You can't hold an ISA jointly with someone else.

Taking money out

You can take money out of an ISA at any time without losing any tax benefits on what's left. The provider may have its own rules or charges, so check the terms.

The catch is putting it back. Unless your ISA is "flexible", money you put back counts as a new payment and uses up allowance again. GOV.UK's own example: pay in £10,000, take out £3,000, and you can only pay in another £10,000 that year, not £13,000. If the ISA is flexible, you can take cash out and put it back in the same tax year without it counting again. Not every provider offers this.

With investments, "taking money out" usually means selling first. If the market is down that week, you sell low. That's the real cost of using an investment ISA as a rainy-day fund.

Moving your ISA

You can move an ISA to another provider. The rule that matters: contact the provider you want to move to and fill in their transfer form. Don't withdraw the money and pay it in yourself. If you do, you can't put that part of your allowance back, and money that was tax-free becomes ordinary money.

Transfers between providers, other than cash ISA to cash ISA, should take no more than 30 calendar days. You can transfer money from this tax year or earlier ones.

When comparing providers, look at how they charge. Some take a percentage of your pot each year, some a flat monthly fee, and the funds have their own charges too. The FCA warns that charges can mount up over time and eat into your returns. A charge that looks tiny on a statement compounds every year, just like returns do.

What the ISA doesn't protect you from

The Financial Services Compensation Scheme can pay up to £85,000 per person, per firm if an authorised investment firm fails and you have a valid claim. It says plainly that it can't accept claims for poor investment performance, because investments can go down as well as up.

That's why the FCA suggests investing over at least five years, and spreading your money across different companies, types of investment and countries. Time and spread don't remove the risk. They give it room to even out.

Stocks and shares ISA or cash ISA?

They do different jobs. A cash ISA is for money you might need soon, or can't afford to see fall: it pays interest and the balance doesn't drop. A stocks and shares ISA is for money you can leave alone for years, in exchange for the chance of higher growth and the certainty of some bumpy years.

Plenty of people use both: cash for the near term, investments for the long term, and the £20,000 allowance split between them. From April 2027, anyone under 65 who wants to use the full £20,000 will need to put at least £8,000 of it into ISAs other than cash ISAs.