TL;DR
- A cash ISA is a UK savings account on which all interest is exempt from income tax.
- The 2025-26 annual subscription limit is 20,000 pounds, shared with other adult ISA types.
- FSCS protects eligible deposits up to 85,000 pounds per person per authorised institution.
- Open to UK-resident individuals aged 18 or over (16+ for Help to Buy and now-closed legacy products).
Last reviewed: May 2026 | Sources: HMRC ISA Manual, ISA Regulations 1998, FSCS
A cash ISA is one of the most widely used UK savings products, yet rules around eligibility, allowance, FSCS treatment and the 2024-25 reform are commonly misunderstood. This guide sets out what a cash ISA actually is in law, how it differs from a standard savings account, who can open one and how the tax-free wrapper interacts with the wider Personal Savings Allowance regime.
What a cash ISA is in law
A cash ISA is a savings deposit held inside the Individual Savings Account tax wrapper established by the Individual Savings Account Regulations 1998 and administered by HMRC. The wrapper exempts interest credited inside the account from UK income tax, with no obligation on the saver to declare it on a self-assessment return. The underlying account is a deposit at an authorised bank, building society or credit union, or held under safeguarding arrangements at an e-money institution authorised by the Financial Conduct Authority.
The legal source is the 1998 regulations as amended, with operational rules set out in the HMRC ISA Manual. For a survey of the current rate landscape on variable-rate accounts, the easy access cash ISA guide on Kael Tripton breaks down provider mechanics and access terms in detail.
Cash ISA vs standard savings account
A standard savings account pays interest into the saver name, and that interest counts towards taxable income for the year. The Personal Savings Allowance of 1,000 pounds (basic rate), 500 pounds (higher rate) and nil (additional rate) shields some of that interest, but anything beyond the PSA is taxed at marginal rates.
A cash ISA bypasses this entirely. Every pound of interest inside the wrapper is tax-free regardless of the saver overall income, and the FSCS limit is identical at 85,000 pounds per authorised institution. The trade-off is the 20,000 pound annual subscription cap. For balances above the PSA threshold and certainly for any higher-rate or additional-rate taxpayer, the ISA wrapper is almost always the more tax-efficient location for cash savings.
RELATED GUIDES: ISA and Savings Guides
- How Many ISAs Can I Have? UK Rules Explained
- How Much Can You Put in an ISA?
- ISA vs Fixed Rate Bond: Key Differences
- ISA Accounts UK: All Types Compared
- Easy Access Savings Accounts UK 2026
- Premium Bonds UK 2026 Guide
Who can open a cash ISA
Adult cash ISAs are open to UK residents aged 18 or over. Crown servants posted overseas and their spouses or civil partners may also subscribe under specific HMRC rules. A National Insurance number is required at account opening, and the account must be held in a single name (joint cash ISAs are not permitted).
Under-18s are not eligible for an adult cash ISA, although they may hold a Junior cash ISA with a separate 9,000 pound annual allowance. Non-UK residents cannot open a new ISA, although existing ISAs remain open and continue to grow tax-free during non-residency.
RELATED GUIDES: Related ISA guides
- Best easy access cash ISA UK rates and providers
- How many ISAs a saver can hold at once
- How much can be paid into an ISA each tax year
- Transferring an ISA between providers
Types of cash ISA available in 2026
Easy access cash ISAs allow withdrawals and additions at any time without penalty, with rates set by the provider on a variable basis. Fixed rate cash ISAs lock the rate in for a defined term (typically 1, 2, 3 or 5 years) and usually restrict withdrawals or charge an interest penalty for early exit. Notice cash ISAs sit between the two, requiring a defined notice period (often 30, 60 or 90 days) before funds are released.
Flexible cash ISAs are a feature, not a separate product type: any of the above can be designated flexible by the provider, allowing withdrawn funds to be replaced in the same tax year without using fresh allowance. Provider participation in the flexible regime is optional.
The 2024-25 reform and FSCS treatment
From 6 April 2024 a saver can subscribe to more than one cash ISA at different providers in the same tax year, provided total subscriptions stay within 20,000 pounds. Before 2024-25 only one cash ISA could be opened or subscribed to per tax year.
FSCS protection is 85,000 pounds per eligible person per authorised institution. Banks sharing a banking licence share a single FSCS limit even when they trade under different brand names. The FSCS register at fscs.org.uk lists each banking licence and the brands it covers, which is essential reading before a saver spreads larger balances. The easy access cash ISA shortlist typically includes FSCS-protected providers only.
Cash ISA vs Premium Bonds
Premium Bonds are issued by NS&I and are backed by HM Treasury rather than the FSCS. Prizes (rather than interest) are tax-free, but there is no guaranteed return: the prize fund rate is a notional headline figure, and individual holders may win nothing in a given month. A cash ISA pays predictable, contractually defined interest within the ISA wrapper. NS&I products do not count against the 20,000 pound ISA allowance.
Disclaimer: This guide is general information about UK cash ISA rules and is not personal financial advice. Tax treatment depends on individual circumstances and may change. Anyone unsure about how the rules apply to their position should speak to a regulated financial adviser or check gov.uk directly.
Frequently Asked Questions
Is cash ISA interest taxable in any circumstances?
Interest credited inside a properly subscribed cash ISA is exempt from UK income tax. The exception is if HMRC voids the ISA for a breach of subscription rules, in which case interest may be subject to tax.
Can a cash ISA be opened jointly with a spouse?
No. Cash ISAs are single-name accounts under the ISA Regulations 1998. Each spouse must hold their own ISA in their own name, with their own 20,000 pound allowance.
Does the Personal Savings Allowance apply inside an ISA?
The PSA applies to non-ISA savings interest. ISA interest is fully tax-free and does not consume any of the PSA, so the PSA remains available for any taxable savings held outside the wrapper.
Is a cash ISA the same as a savings bond?
No. A cash ISA is a tax-free wrapper that can hold easy access, fixed rate or notice savings. A standard fixed rate savings bond is taxable unless held inside an ISA wrapper.
What happens to a cash ISA when the holder dies?
Most ISAs remain tax-advantaged as a Continuing ISA for up to three years after death. A surviving spouse or civil partner gains an Additional Permitted Subscription equal to the value of the ISA at the date of death.
How This Guide Was Verified
This guide is sourced from the Individual Savings Account Regulations 1998 on legislation.gov.uk, the HMRC ISA Manual on gov.uk, the FSCS protected amounts page on fscs.org.uk and the FCA Conduct of Business Sourcebook chapter on retail savings products. All linked sources were checked against the current published version as of May 2026.
