What Is an ISA? A Plain Guide to the UK Tax-Free Wrapper

An Individual Savings Account (ISA) is a tax-free wrapper provided by the UK government. Any interest, dividends, or capital gains earned inside an ISA are completely free from income tax and capital gains tax. You do not even declare ISA income on a tax return.

For the 2026-27 tax year, every UK resident aged 18 or over can contribute up to £20,000 across all their ISAs. The allowance resets each April 6 and cannot be carried forward, use it or lose it. From 6 April 2027 no more than £12,000 of it may go into cash ISAs each year if you are under 65, a change announced at the Autumn Budget 2025; the overall limit is unchanged.

There are four main types. A Cash ISA works like a savings account but the interest is tax-free. A Stocks and Shares ISA lets you hold funds, shares, and bonds, with growth and income sheltered from tax. An Innovative Finance ISA wraps peer-to-peer lending returns. A Lifetime ISA pays a 25% government bonus for first-time buyers and retirement savers, with contributions accepted up to age 50.

You can split your £20,000 allowance across multiple types in the same tax year, and since April 2024 you can open and pay into more than one ISA of the same type at once.

The rule that catches people out is how withdrawals work. Some providers offer flexible ISAs, which let you replace money you take out in the same tax year without eating into your annual limit. Non-flexible ISAs treat any withdrawal as lost allowance for that year. Check which type you hold before you move money around.

A Stocks and Shares ISA suits long-term savings you will not need for several years. A Cash ISA suits short-term savings or an emergency buffer you want guaranteed and accessible. A Lifetime ISA suits a first home or retirement, but withdrawing for any other reason triggers a 25% penalty, so it is the wrong home for money you might need early.