Cash ISAs explained: how does a cash ISA work, and what changes in 2027?

By FastBuySale Newsroom · 5 Nov 2026 · 42m ago

How a cash ISA works

Cash ISAs explained simply: a cash ISA is a savings account from a bank, building society or National Savings and Investments where the interest is completely free of UK tax. In the 2026 to 2027 tax year you can put up to £20,000 into ISAs in total, and all of it can go into cash ISAs.

That will change. From 6 April 2027 the government is cutting the annual cash ISA limit to £12,000 for savers under 65, while keeping the overall ISA allowance at £20,000 and the full £20,000 cash limit for people 65 and over, according to HM Revenue and Customs (HMRC).

official UK government guidance says you do not pay tax on interest on cash in an ISA, and if you complete a Self Assessment tax return you do not need to declare it. Your ISA does not close at the end of the tax year: money stays tax-free for as long as you keep it in the account.

There are four types of ISA: cash, stocks and shares, innovative finance and Lifetime ISA. Cash ISAs can hold savings in bank and building society accounts and some National Savings and Investments products.

Who can open one: you must be 18 or over, and resident in the UK, or a Crown servant or armed forces member (or their spouse or civil partner) if you live abroad. You cannot hold an ISA jointly with someone else. Children under 18 can have a Junior ISA instead.

The tax year runs from 6 April to 5 April, so each new allowance starts on 6 April. Any allowance you do not use by 5 April is lost; it cannot be carried forward to the next tax year, so savers with spare cash often top up before the deadline.

Readers evaluating Cash ISA should separate marketing claims from the actual rule text that governs their account or product. When two summaries disagree, the governing document or statute wins. If a rule depends on your age, filing status, or income band, re-check it when any of those facts change. Life events quietly move people across thresholds they last reviewed years earlier.

Educational explainers like this one cannot replace personalized advice for complex situations such as divorce orders, inherited accounts, or cross-border tax residency. Escalate those cases to a qualified professional. When in doubt about a number that changes every year, describe your plan qualitatively first, then look up the current official figure for the tax year you care about before you act.

The £20,000 allowance and how to split it

Every tax year you can save up to £20,000 in one account or split the allowance across several, official UK government guidance says. You can pay into more than one cash ISA in the same year.

official UK government guidance's own examples: you could save £15,000 in a cash ISA, £2,000 in a stocks and shares ISA and £3,000 in an innovative finance ISA; or £10,000 in one cash ISA, £3,000 in another cash ISA and £7,000 in a stocks and shares ISA.

A Lifetime ISA has its own £4,000 yearly cap that counts inside the £20,000, and you can only pay into one Lifetime ISA each tax year.

Withdrawals: with an ordinary cash ISA, money you take out still counts towards that year's allowance. Some providers offer 'flexible' ISAs, where you can withdraw and replace cash in the same tax year without using extra allowance. Check whether your account is flexible before withdrawing.

A useful habit is to write down your goal, time horizon, and cash buffer before you change any election related to Cash ISA. Decisions made during a stressful week are the ones people reverse later at a cost. Educational explainers like this one cannot replace personalized advice for complex situations such as divorce orders, inherited accounts, or cross-border tax residency. Escalate those cases to a qualified professional.

Types of cash ISA and transfers

Easy-access cash ISAs let you withdraw at any time, usually at a variable rate. Notice cash ISAs need advance notice. Fixed-rate cash ISAs lock your money for a set term, often one to five years, in return for a fixed rate, with a penalty for early access.

Transfers: you can move ISA savings between providers without losing the tax-free status. Use the new provider's ISA transfer process; if you withdraw the money yourself, it loses its ISA wrapper and counts as a new subscription when paid back in.

Safety: deposits with a UK-authorised bank or building society are protected by the Financial Services Compensation Scheme (FSCS) up to its limit per person per banking licence, and National Savings and Investments is backed by HM Treasury. The FSCS says eligible deposits are automatically protected up to £120,000 per person, per bank, building society or credit union, so savers with more than that may spread money across separately licensed providers.

Comparing rates: work out what a rate is worth with the and check whether it beats inflation using the

Keep digital and paper copies of confirmations after every change. Screenshots of election pages, email receipts, and year-end statements make tax season and job changes far less chaotic. Compare fees the same way you would compare two similar listings before you buy: look at what you pay each year, what you get, and whether a simpler option meets the same need.

What changes from 6 April 2027

At Autumn Budget 2025 the government announced that the annual cash ISA limit will fall to £12,000 for people under 65 from 6 April 2027, within the unchanged £20,000 overall limit. HMRC's policy paper says people aged 65 and over keep a £20,000 cash ISA limit, from the start of the tax year in which they turn 65.

To stop people getting round the cap, savers under 65 will not be able to transfer money from stocks and shares or innovative finance ISAs into cash ISAs, and interest paid on cash held in a stocks and shares ISA will face a flat charge of 22%. Money you already hold in cash ISAs is not affected.

Worked example: Sophie, 34, wants to save £20,000 in 2027 to 2028. She can put up to £12,000 into cash ISAs and the remaining £8,000 into a stocks and shares or innovative finance ISA. Her father, 66, can still put the full £20,000 into cash ISAs.

Who a cash ISA suits: savers building an emergency fund, people saving for a goal within a few years, and anyone whose interest could exceed the Personal Savings Allowance. official UK government guidance sets that allowance by tax band: £1,000 of interest a year for basic-rate taxpayers, £500 for higher-rate taxpayers and £0 for additional-rate taxpayers. official UK government guidance gives the example of a basic-rate taxpayer earning £1,300 of interest outside an ISA: the first £1,000 is tax-free and the remaining £300 is taxed at 20%, or £60. Inside a cash ISA, none of that interest would be taxed. For other UK savings options, read and and browse more money guides at

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If a rule depends on your age, filing status, or income band, re-check it when any of those facts change. Life events quietly move people across thresholds they last reviewed years earlier. Automation helps. Calendar reminders for annual reviews, automatic transfers, and beneficiary checkups reduce the chance that a good plan dies from neglect.

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