ISA vs. Savings Account: Which Should You Use?

ISAs and standard savings accounts both let your money grow, but the key difference is tax treatment — and for most savers below the Personal Savings Allowance, that difference matters less than people often assume.

What an ISA actually does

A Cash ISA shelters interest earned from Income Tax entirely, regardless of how much interest you earn within it. You can contribute up to the annual ISA allowance (£20,000 across all ISA types combined for most adults) each tax year, and unused allowance doesn't carry forward.

A Major Change Is Coming: Cash ISA Allowance Cut From April 2027

Confirmed at the Autumn Budget 2025 and detailed further by HMRC and gov.uk through 2026: from 6 April 2027, savers under 65 will only be able to put up to £12,000 of their £20,000 total ISA allowance into a Cash ISA specifically — the remaining £8,000 must go into a Stocks & Shares ISA, Innovative Finance ISA, or Lifetime ISA if you want to use your full allowance. The overall £20,000 ISA limit itself isn't changing, only how much of it can sit in cash. Savers aged 65 and over are exempt and keep the full £20,000 Cash ISA allowance. For the current 2025/26 and 2026/27 tax years, the full £20,000 Cash ISA allowance remains available to everyone — this is a genuine "use it while you can" window if a large Cash ISA balance is part of your plan.

Separately, from 6 April 2026, tax on savings interest held outside an ISA is rising by 2 percentage points across the board, while the Personal Savings Allowance itself stays frozen at £1,000/£500 — making the case for using your ISA allowance somewhat stronger going forward, even before the 2027 cash-specific restriction takes effect.

The Personal Savings Allowance changes the calculus

Most savers already get some tax-free interest outside an ISA: basic-rate taxpayers can earn £1,000/year in savings interest tax-free, higher-rate taxpayers £500/year, and additional-rate taxpayers get no allowance at all. For many basic-rate taxpayers with modest savings, a standard savings account may generate no taxable interest anyway — making the ISA's tax shelter less immediately valuable than it sounds, at least until the 2026 savings-tax-rate increase and 2027 Cash ISA cap changes described above take effect.

When an ISA clearly wins

Higher earners (higher or additional rate taxpayers) with meaningful savings balances benefit more directly, since their Personal Savings Allowance is smaller or nonexistent. Anyone with savings large enough that the interest would exceed their allowance in a standard account benefits from moving that interest into a tax-free ISA wrapper instead.

Rate differences matter too

ISA rates and standard savings rates move independently — sometimes standard easy-access accounts offer better headline rates than comparable ISAs, and sometimes the reverse. Comparing the actual rate on offer matters as much as the tax treatment, especially for savers who wouldn't owe tax on the interest either way.

A Lifetime ISA is a different product entirely

Don't confuse a standard Cash ISA with a Lifetime ISA (LISA), which adds a 25% government bonus specifically for first-time home purchase or retirement savings, with its own separate £4,000/year contribution limit and withdrawal restrictions. The LISA itself is also being phased out: the government has confirmed it will be replaced by a new, simpler first-time-buyer-focused product from April 2028, following a consultation published in early 2026 — if a LISA is part of your plan, it's worth watching this transition closely rather than assuming the current product and rules will remain unchanged.

Model how your savings grow at a given rate with the Savings Calculator, or compare current rates with Bank Interest Rates.