ISAs Explained: The Complete UK Guide to Tax-Free Saving and Investing

An ISA explained in one sentence: it is a wrapper that shelters your savings and investments from UK tax, and every adult gets a fresh allowance to fill each year. No tax on the interest, no tax on dividends, no capital gains tax when your investments grow. That is the whole appeal, and for most people it is the first place money should go before any taxable account.

This guide covers how ISAs actually work in the 2026/27 tax year, the four main types, the significant change coming in April 2027, and how to use the wrapper sensibly rather than just parking cash and forgetting it.

What an ISA is (and isn’t)

An ISA (Individual Savings Account) is not an investment in itself. It is a tax-free container you put savings or investments inside. Think of it as a box: the box is the tax shelter, and what you fill it with (cash, funds, shares) is up to you. Everything held inside grows free of income tax and capital gains tax, and you never have to declare it on a tax return.

Two rules underpin everything else:

• You get one allowance per tax year, and it runs from 6 April to 5 April.
• Use it or lose it. Unused allowance does not carry over. On 6 April a new allowance starts and last year’s is gone.

The 2026/27 ISA allowance

For the 2026/27 tax year, the total ISA allowance is £20,000. You can pay that in across the different ISA types in any split you like, as long as the combined total does not exceed £20,000. You can confirm the current figure on GOV.UK.

Since April 2024, you can also pay into more than one ISA of the same type in a single tax year, so you are no longer locked to one cash ISA and one stocks and shares ISA provider per year. The £20,000 ceiling still applies across all of them together.

The four main ISA types

Cash ISA. A savings account inside the tax wrapper. Interest is tax-free. Best for money you cannot afford to see fall, such as an emergency fund or a deposit you need within a few years.

Stocks and Shares ISA. Holds investments (funds, ETFs, individual shares) with all growth and dividends tax-free. Suited to money you can leave invested for the long term, typically five years or more. Our guides to the best stocks and shares ISA and the cheapest platforms go deeper.

Lifetime ISA (LISA). For a first home or retirement. You can pay in up to £4,000 a year (which counts toward your £20,000 total), and the government adds a 25% bonus. You must open it before age 40 and make the first payment before then. The catch: withdraw for anything other than a first home or after age 60 and you pay a withdrawal charge that can leave you with less than you put in.

Innovative Finance ISA. Holds peer-to-peer loans. Higher risk and far less common, and not where most people should start.

There is also the Junior ISA for under-18s, which has its own separate allowance.

The big change coming in April 2027

This is the part worth acting on. In the Autumn 2025 Budget, the Chancellor announced that from 6 April 2027 the cash ISA allowance for people under 65 will fall from £20,000 to £12,000. The overall £20,000 ISA allowance stays, but the portion you can hold in cash drops, with the balance intended to be used for stocks and shares ISAs instead. If you are 65 or over, your cash ISA limit stays at £20,000.

What this means in practice: if you rely heavily on cash ISAs and are under 65, the 2026/27 year is the last with the full £20,000 cash allowance. It is worth thinking now about whether more of your long-term money belongs in a stocks and shares ISA, where the allowance is unaffected.

Flexible ISAs and transfers

Some ISAs are “flexible”, meaning you can withdraw money and pay it back within the same tax year without it counting twice against your allowance. Not all providers offer this, so check before you rely on it.

If you want to move an existing ISA to a better rate or a cheaper platform, never simply withdraw and re-deposit, as that uses up fresh allowance and loses the tax protection on older years. Always use the official ISA transfer process, which your new provider arranges. Our guide on how to transfer a stocks and shares ISA walks through it.

How to use your ISA well

• Match the type to the timeframe. Short-term money and emergency funds belong in a cash ISA; long-term money belongs in a stocks and shares ISA where it has years to grow.
• Fill the wrapper before taxable accounts. With dividend and capital gains tax allowances now small, sheltering investments inside an ISA matters more than it used to.
• Automate contributions. Regular monthly payments spread your investing across the year and stop you scrambling to use the allowance in March.
• Do not chase the LISA bonus blindly. The 25% bonus is generous, but the withdrawal charge makes it the wrong home for money you might need for anything other than a first home or retirement.

Frequently asked questions

What is an ISA in simple terms? An ISA is a tax-free wrapper for your savings or investments. Any interest, dividends or growth inside it is free of UK tax, and you never declare it on a tax return. Each adult gets one allowance per tax year to fill.

How much can I put in an ISA in 2026/27? The total ISA allowance for 2026/27 is £20,000, which you can split across cash, stocks and shares, and innovative finance ISAs, plus up to £4,000 in a Lifetime ISA, as long as the combined total stays within £20,000.

Is the cash ISA allowance changing? Yes. From 6 April 2027, the cash ISA allowance for under-65s falls from £20,000 to £12,000, while the overall £20,000 ISA allowance remains. Those aged 65 and over keep the £20,000 cash limit.

Can I have more than one ISA? Yes. Since April 2024 you can pay into multiple ISAs of the same type in one tax year, across different providers. The single £20,000 total allowance still applies across all of them combined.

What happens if I don’t use my ISA allowance? You lose it. The allowance does not carry over to the next year. On 6 April a fresh allowance begins and any unused amount from the previous year is gone for good.

The bottom line

With ISAs explained, the strategy is simple: use the £20,000 allowance each year, put short-term money in a cash ISA and long-term money in a stocks and shares ISA, and transfer rather than withdraw when you switch. Keep an eye on the April 2027 cash ISA cut if you are under 65, because it changes where your long-term savings are best held. The wrapper is one of the few genuinely tax-free options UK savers get, so it pays to fill it deliberately.