Is an ISA worth it?

Is an ISA worth it?

An ISA is worth what the tax it removes is worth, set against what it costs in flexibility. gov.uk says you do not pay tax on interest on cash in an ISA, or on income or capital gains from investments in one, and that if you complete a tax return you do not need to declare any of it. Whether that is worth having depends on the saver’s own balance, tax band and plans, so this page is general information, not advice.

For many savers the tax involved is small or nil in 2026/27. HM Treasury’s policy explainer says “Over 90% of UK taxpayers do not pay savings tax”. Outside an ISA, interest within your allowances is not taxed, so an ISA only saves tax on the interest above them.

The numbers behind the answer

Personal Savings Allowance, 2026/27

£1,000 / £500 / £0

Basic, higher and additional rate taxpayers, on interest outside an ISA

Starting rate for savings

Up to £5,000

If other taxable income is under £17,570

Dividend allowance outside an ISA

£500

On dividends outside an ISA

Capital Gains Tax annual exempt amount

£3,000

Gains above it can be taxed outside an ISA

ISA allowance, 2026/27

£20,000

Across all your ISAs

Cash ISA limit from 6 April 2027

£20,000

Planned cut to £12,000 cancelled

Who gets the most from an ISA?

An ISA saves the tax that would otherwise be due, so the saving is biggest where that tax is biggest:

• Larger balances. More savings earn more interest, and tax starts once the interest passes the allowance.
• Higher and additional rate taxpayers. The Personal Savings Allowance falls from £1,000 for a basic rate taxpayer to £500 for a higher rate taxpayer and £0 for an additional rate taxpayer, so more of the interest can be taxed.
• Investors. Outside an ISA, dividends above the £500 dividend allowance and gains above the £3,000 Capital Gains Tax annual exempt amount can be taxed. Inside one, gov.uk says there is no tax on income or capital gains from investments.
• From 6 April 2027. The Budget documents of 28 October 2026 say savings tax rates rise to 24%, 44% and 49% from April 2027, so interest above the allowance costs more tax outside an ISA.

How much tax could an ISA save?

A worked example. This is an illustration, not a forecast, and the 4% is an example rate, not a rate on offer. It takes £30,000 held outside an ISA for a year, which at 4% earns £1,200 of interest. It assumes no other savings interest, and no Personal Allowance or starting rate for savings left to cover it, so only the Personal Savings Allowance covers the interest. The rest is taxed at the rate for the saver’s band.

In a Cash ISA the same £1,200 is tax-free, so the tax in each row is what the ISA would save in a year. The saving depends on the rate, the balance and any other savings interest. Tax treatment depends on your circumstances and may change. The savings tax calculator works out the tax on your own interest.

When does an ISA add little?

When interest stays inside the allowances, there is no tax for an ISA to remove. £10,000 earning an example 4% is £400 a year. If that were a saver’s only savings interest, it would sit inside both the £1,000 basic rate allowance and the £500 higher rate allowance. The starting rate for savings can cover more: up to £5,000 of interest if other taxable income is under £17,570.

That can change. The allowance depends on the tax band, so it falls if income rises into a higher band. A larger balance or a higher rate means more interest, and from 6 April 2027 the tax on interest above the allowance rises. See the Personal Savings Allowance and do you pay tax on ISA interest.

What do you give up with an ISA?

• Fixed terms. Fixed rate ISAs usually charge for early access. The fixed rate ISA penalty calculator works out what a charge could cost.
• Putting money back. gov.uk says that if you withdraw from a non-flexible ISA, you cannot put the money back without using allowance. See flexible ISAs.
• A limit on what goes in. It is £20,000 a year across all ISAs in 2026/27. The Cash ISA limit stays £20,000, so all of it can go into cash. Savings above the limit stay outside an ISA, where the allowances above apply.
• A better rate elsewhere. An ISA is only better if its rate after tax beats the alternative after tax.

A taxable savings account can pay a higher rate than an ISA, and if its interest stays inside the allowances there is no tax to take off. On the £30,000 example, an ISA paying 4% earns £1,200 tax-free. A taxable account would need to pay about 4.17% to leave a basic rate taxpayer with the same amount after tax in 2026/27, and about 5.56% for a higher rate taxpayer. The ISA vs savings account calculator compares two rates after tax.

What about investment ISAs?

A Stocks and Shares ISA holds investments instead of cash. The tax rule is the same: gov.uk says you do not pay tax on income or capital gains from investments in an ISA. Outside one, dividends above the £500 dividend allowance and gains above the £3,000 Capital Gains Tax annual exempt amount can be taxed, so the saving can grow with the investments.

Tax is only part of the picture. The value of investments can fall as well as rise, and you may get back less than you paid in. An ISA removes tax on income and gains, not the risk of loss. Cash ISA or Stocks and Shares ISA compares the two on risk, access and protection.

What changes on 6 April 2027?

Two changes matter for this question.

Savings tax rates rise. The Budget documents of 28 October 2026 say savings tax rates rise to 24%, 44% and 49% from April 2027, up from 20%, 40% and 45% in 2026/27. That applies to interest outside an ISA. In the worked example, the tax on £1,200 of interest rises from £40 to £48 for a basic rate taxpayer, from £280 to £308 for a higher rate taxpayer and from £540 to £588 for an additional rate taxpayer. See savings tax 2027.

The Cash ISA limit stays. A planned cut to £12,000 for savers aged 64 or under was cancelled in the Budget on 28 October 2026, so the limit stays £20,000. See the Cash ISA limit.

Tax rules can change at a Budget, and the most recent was on 28 October 2026. Tax treatment depends on your circumstances and may change.

How can you check your own numbers?

The ISA vs savings account calculator compares an ISA with a taxable account at rates you choose, after tax. The savings tax calculator works out the tax on your own interest. For the rules, see do you pay tax on ISA interest and the Personal Savings Allowance.