An Individual Savings Account — or ISA — is one of the most valuable savings tools available to UK residents. The key benefit is straightforward: any interest, dividends or capital gains you earn within an ISA are completely free from UK tax. You do not need to declare ISA income on a tax return.
There are several types of ISA available, but this guide focuses on the Cash ISA — the simplest and most widely used form.
What is a Cash ISA?
A Cash ISA is a savings account that works like a standard savings account, except the interest you earn is tax-free. You deposit cash, the account earns interest, and you pay no tax on that interest regardless of how much you earn or save.
Cash ISAs are available from banks, building societies and other savings providers. They come in two main forms: easy-access Cash ISAs, which allow you to withdraw money at any time, and fixed-rate Cash ISAs, which lock your money away for a set term (typically one to five years) in exchange for a higher interest rate.
The ISA allowance
Each tax year (which runs from 6 April to 5 April), every UK resident aged 18 or over can save up to the annual ISA allowance across all their ISAs. The current ISA allowance is £20,000 per tax year — check gov.uk for the current figure as this can change.
This allowance is per person, not per account. You can split the allowance across different types of ISA in the same tax year — for example, some in a Cash ISA and some in a Stocks and Shares ISA — as long as the total does not exceed £20,000.
You cannot carry unused ISA allowance from one tax year to the next. If you only use £5,000 of your £20,000 allowance this year, you cannot add the remaining £15,000 to next year's allowance.
Who can open a Cash ISA?
To open a Cash ISA, you must be:
- Aged 18 or over
- A UK resident
There is also a Junior ISA (JISA) for children under 18, which has a separate, lower annual allowance.
Do you actually need an ISA?
Since 2016, most UK savers have also been entitled to a Personal Savings Allowance (PSA). This allows basic rate taxpayers to earn £1,000 in savings interest per year tax-free (outside of an ISA), and higher rate taxpayers to earn £500. Additional rate taxpayers receive no PSA.
For many people with modest savings, the PSA means they will not pay tax on their savings interest regardless of whether they use an ISA. However, if you have significant savings, earn a higher income, or want to protect future returns from tax — particularly if interest rates rise or your savings grow — an ISA offers a valuable tax shelter.
An ISA is also useful if you are saving for the long term. Money inside an ISA retains its tax-free status indefinitely, meaning gains compound without tax drag over many years.
Easy-access vs fixed-rate Cash ISAs
Easy-access Cash ISA
Allows you to deposit and withdraw money freely. Interest rates are variable, meaning they can change at any time. This is the most flexible option and works well for emergency funds or money you may need at short notice.
Fixed-rate Cash ISA
Locks your money in for a fixed term — typically one, two or five years — in exchange for a guaranteed interest rate that will not change during the term. Withdrawals are restricted or penalised before the term ends. This option works best for money you are confident you will not need for the duration of the term.
Can you transfer a Cash ISA?
Yes. You can transfer your Cash ISA to a different provider at any time without losing your tax-free status or counting against your annual allowance. You must use the official ISA transfer process — withdrawing money and depositing it in a new account does not count as a transfer and may lose you the tax benefit.
You can also transfer from a Cash ISA to a Stocks and Shares ISA, or vice versa. Transfers can include money saved in previous tax years as well as the current year.
What about other types of ISA?
Beyond the Cash ISA, there are several other ISA types:
- Stocks and Shares ISA — invests your money in the stock market rather than holding it as cash. Potentially higher returns but with investment risk.
- Lifetime ISA (LISA) — for people aged 18 to 39, designed for buying a first home or retirement. The government adds a 25% bonus on contributions up to £4,000 per year. There are penalties for withdrawing for other purposes.
- Innovative Finance ISA — invests in peer-to-peer lending. Higher risk than Cash ISAs.
- Junior ISA — for children under 18. Parents or guardians can open one on their behalf.
All ISA types share the same overall annual allowance of £20,000 per tax year.