An Individual Savings Account, or ISA, is one of the simplest tax breaks the UK government offers. The idea is easy to grasp: any interest, dividends, or growth you earn inside an ISA is completely free of tax. No income tax, no capital gains tax, nothing. And every year on 6 April, your allowance resets.
For the 2026/27 tax year, that allowance is still £20,000. But with savings rates higher than they have been for over a decade, and persistent talk of reform, it is worth taking a fresh look at how to use yours. Here is a plain-English guide.
What Counts as Your £20,000 Allowance
The £20,000 is the total you can pay in across all your ISAs in a single tax year. You do not get £20,000 per ISA — it is one combined pot. You can split it however you like between the main types:
- Cash ISA: works like a normal savings account, but the interest is tax-free
- Stocks and shares ISA: you invest in funds or shares, and any growth or dividends are tax-free
- Lifetime ISA: for buying a first home or saving for retirement, with a 25% government bonus (subject to a separate £4,000 limit)
- Innovative finance ISA: for peer-to-peer lending, which carries more risk
Since April 2024, you have been able to pay into more than one ISA of the same type in a single year, which gives you more flexibility to chase the best rates without losing your tax shelter.
One point trips a lot of people up: the allowance is about money paid in, not the balance you hold. If you put in £20,000 and then withdraw £5,000, you cannot simply pay that £5,000 back unless your ISA is a 'flexible' one. Flexible ISAs let you take money out and replace it in the same tax year without it counting again towards your limit, which is handy if you dip into your savings now and then. It is worth checking whether yours is flexible before you move money around.
Why an ISA Matters More When Savings Rates Are High
A few years ago, when savings accounts paid almost nothing, the tax saving on a cash ISA felt trivial. That has changed. With easy-access accounts paying around 4% in 2026, the interest you earn can quickly use up your Personal Savings Allowance — the amount of savings interest you can earn tax-free outside an ISA.
The Personal Savings Allowance is £1,000 for basic-rate taxpayers and £500 for higher-rate taxpayers. Additional-rate taxpayers get nothing at all. At 4% interest, a basic-rate taxpayer only needs around £25,000 in ordinary savings before they start paying tax on the interest. Anything inside an ISA does not count towards that limit, so it stays tax-free no matter how much you hold.
You can see how your savings grow over time with our compound interest calculator, which shows the powerful effect of leaving your money to build year after year.
A worked example
Imagine you are a higher-rate taxpayer with £30,000 in an ordinary easy-access account paying 4%. That earns you £1,200 of interest in a year. Your Personal Savings Allowance as a higher-rate taxpayer is only £500, so £700 of that interest is taxable. At the 40% higher rate, that is a tax bill of £280 on money you barely had to lift a finger to earn. Move that same £20,000 of it into a cash ISA paying the same 4%, and the £800 of interest it produces is completely tax-free — wiping out most of that bill straight away. Over several years, that saving compounds into a meaningful sum.
Cash ISA or Stocks and Shares ISA?
This is the question most people wrestle with, and there is no single right answer. It depends on your timescale and how comfortable you are with risk.
Choose cash if
You might need the money within the next few years, or you simply cannot stomach the idea of the balance dropping. Cash is safe, predictable, and protected up to £85,000 per bank under the Financial Services Compensation Scheme. The downside is that, after inflation, your real return may be modest.
Choose stocks and shares if
You are investing for five years or more and can ride out the ups and downs of the market. Historically, shares have beaten cash and inflation over the long run, but there are no guarantees, and the value can fall as well as rise.
Many people sensibly use both: cash for their emergency fund and short-term goals, and a stocks and shares ISA for longer-term wealth building.
The cost of charges
One thing to watch with a stocks and shares ISA is fees. Providers charge a platform fee, and the funds you choose carry their own yearly charge. These sound small — often well under 1% — but over twenty or thirty years they can quietly eat into a chunk of your returns. It pays to compare providers and lean towards low-cost funds, especially if you are investing for the long haul. A cash ISA, by contrast, usually has no charges at all, so the headline rate is what you get.
The Rumoured Cash ISA Changes
There has been ongoing speculation that the government may cut the amount you can put into a cash ISA each year, while keeping the overall £20,000 limit. The thinking is to nudge savers towards investing in shares, which supports UK businesses.
Nothing has been confirmed for 2026/27, and the full £20,000 can still go into cash if you wish. But if you rely heavily on cash ISAs, it is worth keeping an eye on future Budget announcements. As ever, we would caution against making rushed decisions based on rumours — wait for the actual rules before changing your plans.
How an ISA Fits With the Rest of Your Money
An ISA is just one tool. Before filling yours, it is worth checking the bigger picture:
- If your employer matches pension contributions, that is usually the first place your money should go — our pension calculator shows the tax relief on offer
- If you hold investments outside an ISA, you may face capital gains tax when you sell, which an ISA avoids entirely
- Clearing expensive debt, such as credit cards, almost always beats saving, because the interest you pay is higher than what you can earn
Check that your tax code is correct too, so you are not overpaying tax elsewhere and leaving yourself less to save in the first place.
Common Mistakes to Avoid
An ISA is simple, but a few easy slips can cost you. Watch out for these:
- Leaving it to the last minute: the allowance vanishes at midnight on 5 April. If you are paying in near the deadline, do not rely on a transfer clearing in time
- Withdrawing then trying to repay in a non-flexible ISA: unless your ISA is flexible, money you put back counts again towards your £20,000
- Letting old cash ISAs languish on poor rates: you can transfer an old ISA to a better-paying one without using any new allowance, as long as you ask the new provider to handle the transfer rather than withdrawing the cash yourself
- Forgetting the Lifetime ISA £4,000 sits inside the £20,000: it is not extra on top
Transferring is the one that catches people out most. If you simply withdraw the money and pay it into a new ISA yourself, it loses its tax-free status and uses up fresh allowance. Always use the official transfer process instead.
The Bottom Line
The ISA allowance is a genuine, no-strings tax break, and in a world of higher savings rates it is more valuable than it has been for years. Use as much of your £20,000 as you reasonably can, split it between cash and investments to suit your goals, and remember that the allowance does not roll over — if you do not use it by 5 April, it is gone for good.