Cash ISA vs Savings Account: Is Tax-Free Worth It?

The Personal Savings Allowance changed everything

Before 2016, Cash ISAs were essential for anyone earning interest on savings. Then the Personal Savings Allowance (PSA) arrived and made them unnecessary for millions of people.

Basic rate taxpayers can earn up to £1,000 in savings interest per year tax-free through the PSA. Higher rate taxpayers get £500. Additional rate taxpayers get nothing.

At a 4.5% interest rate, a basic rate taxpayer would need over £22,000 in savings before they earn more than £1,000 in interest and start paying tax. Most people don’t hit that threshold.

When a Cash ISA makes sense

Higher rate taxpayers. With only £500 of PSA, a higher rate taxpayer with £12,000+ in savings at 4.5% is already paying tax on their interest. Moving cash into a Cash ISA eliminates that.

Additional rate taxpayers. No PSA at all. Every pound of interest is taxed at 45%. A Cash ISA is worth it from the first penny.

Large emergency funds. If you keep £30,000-£50,000 in cash (perhaps saving for a home deposit while maintaining an emergency fund), even basic rate taxpayers will exceed their PSA. A Cash ISA shelters the excess.

Rate drops. If savings rates fall below 3%, the PSA covers a larger balance before tax kicks in. But the Cash ISA rates also tend to be lower in that environment, so the benefit is smaller.

When a regular savings account wins

Most basic rate taxpayers. If your total savings earn under £1,000 in interest annually, a Cash ISA gives you zero tax benefit. Meanwhile, regular savings accounts and fixed-rate bonds often pay 0.25-0.50% more than the best Cash ISA equivalents.

That rate difference matters. On £15,000, an extra 0.5% is £75 per year — money you’d keep because you’re not paying tax on either option.

Bonus accounts. Some regular savings accounts offer introductory rates of 5-6% for 12 months (usually capped at £250-£500 per month in deposits). These beat most Cash ISAs during the bonus period.

The real cost: wasting your ISA allowance

This is the argument most people miss. Your £20,000 annual ISA allowance is shared across all ISA types — Cash, Stocks & Shares, and Lifetime. Every pound in a Cash ISA is a pound not in a Stocks & Shares ISA.

Over 20 years, a Stocks & Shares ISA invested in a global index fund has historically returned 7-10% annually (before inflation). A Cash ISA at 4% doesn’t come close to that over the long term. The tax-free shelter is far more valuable on investment growth — where you’d otherwise pay capital gains tax and dividend tax — than on cash interest, which the PSA already covers.

If you need a Cash ISA for large short-term balances, consider splitting your ISA allowance: keep enough in a Cash ISA to stay under the PSA on your non-ISA savings, and put the rest into Stocks & Shares.

The numbers for 2025-26

Here’s the break-even point — the savings balance where your interest exceeds the PSA and a Cash ISA starts saving you tax:

Tax band	PSA	Break-even at 4.5% rate
Basic rate (20%)	£1,000	~£22,200
Higher rate (40%)	£500	~£11,100
Additional rate (45%)	£0	£0 (any interest is taxed)

If your savings are below your break-even, a Cash ISA provides no tax advantage. Pick whichever account — ISA or regular — offers the best rate.

The bottom line

For basic rate taxpayers with modest savings, skip the Cash ISA and use a higher-paying regular account. Save your ISA allowance for investments where the tax shelter is worth far more. For higher earners or people with significant cash holdings, a Cash ISA remains a useful part of the toolkit — just be aware of what it costs you in lost investment ISA space.