A Cash ISA is a savings account where you pay no UK income tax on the interest earned. Unlike a standard savings account, where interest above your Personal Savings Allowance is taxable, interest in a Cash ISA is tax-free for life — regardless of how large the account grows.
How a Cash ISA differs from a standard savings account
In a standard savings account, interest is tax-free up to your Personal Savings Allowance — £500 per year for basic rate taxpayers, £1,000 for those earning below the higher rate threshold. Above this, interest is taxed at your marginal rate. For most people with modest savings, this allowance means they pay no tax on savings interest anyway — making the immediate tax advantage of a Cash ISA less dramatic than it sounds.
The advantage of a Cash ISA becomes more significant over time as savings grow. If you build £30,000, £50,000 or more in savings, the interest earned will exceed the Personal Savings Allowance and a Cash ISA provides meaningful tax protection. For younger savers with smaller amounts, the priority is often a higher interest rate rather than the ISA wrapper itself.
How to open a Cash ISA
Cash ISAs are available from most UK banks and building societies. You can open one online, by phone or in branch. You will need your National Insurance number and standard identity documents. The process typically takes less than 20 minutes online.
The annual ISA allowance is £20,000. You can deposit up to this amount across all your ISAs combined in each tax year (6 April to 5 April). You cannot deposit more than this into ISAs in a single year — the unused allowance does not carry forward.
Fixed rate vs easy access Cash ISAs
- Easy-access Cash ISAs: money available within 1-3 working days, interest rate can change, typically lower rate than fixed
- Fixed-rate Cash ISAs (Fixed Rate Bonds): money locked for a set period (1, 2, or 3 years typically), higher rate guaranteed for the term, early withdrawal usually incurs a penalty
- For emergency funds: easy-access only — locked savings cannot serve as an emergency fund
- For money you can leave untouched: fixed rate ISAs typically offer the best rates
Is a Cash ISA worth it?
For most people with savings below £20,000, the choice between a Cash ISA and a standard savings account often comes down to interest rate rather than tax wrapper. Compare current rates on FCA-regulated comparison sites and choose whichever offers the best AER. If rates are similar, the ISA offers better long-term protection as savings grow.
General guidance only — not regulated financial advice.