The £20,000 ISA allowance: how it works, and what actually counts

The ISA allowance is the single most valuable thing in UK personal finance that most people only half understand. It is worth £20,000 a year, it resets every April, and it cannot be recovered once the tax year ends.

The confusion is rarely about the number. It is about what uses it up.

One allowance, several accounts

You have one £20,000 allowance for the 2026/27 tax year, not one per account. It can be spread across the different ISA types — cash, stocks and shares, innovative finance, and Lifetime ISA (which has its own £4,000 cap counting toward the same total) — in whatever combination you choose.

So £12,000 into a cash ISA and £8,000 into a stocks and shares ISA uses the full allowance. So does £20,000 into either one alone.

What counts, and what doesn't

This is where money quietly disappears.

Counts against your allowance:

• New money paid in from your bank account
• Regular monthly contributions
• Money moved from a general investment account into an ISA (the "Bed and ISA" manoeuvre)

Does not count:

• Transfers between ISAs. Moving an existing ISA from one provider to another does not touch this year's allowance — provided you use the official transfer process. Withdrawing the money yourself and paying it back in does, which is the single most expensive mistake in this area.
• Growth inside the ISA. If £20,000 becomes £24,000, the extra £4,000 has not used anything.
• Dividends and interest paid inside the wrapper and left there.

The flexible ISA question

Some ISAs are flexible. With a flexible ISA, money you withdraw can be replaced in the same tax year without using fresh allowance. Withdraw £5,000 in June, put it back by 5 April, and your allowance is untouched.

With a non-flexible ISA, that same £5,000 replacement consumes £5,000 of allowance. The rules are identical in law; the difference is entirely whether your provider offers flexibility. It is a single line in the terms, and it materially changes how the account behaves.

Worth checking before you withdraw, not after.

Multiple ISAs of the same type

Rules introduced in recent years allow paying into more than one ISA of the same type within a tax year, subject to the overall £20,000 limit. Not every provider supports this, and some still operate on the older one-per-type assumption in their systems.

The practical effect is more freedom to open a better account mid-year — but also more places to lose track of how much allowance you have actually used.

Why the tracking is the hard part

The allowance rules are not complicated. Knowing where you stand against them is.

If you have a cash ISA with your bank, a stocks and shares ISA on a platform, and a Lifetime ISA somewhere else, no single institution can tell you how much of the £20,000 you have used. Each one sees only its own slice. HMRC reconciles it after the year ends — which is the wrong time to discover an overpayment.

That is a straightforward data problem, and it is one of the first things Neo-Invest.AI is being built to solve: one figure, all providers, all year.

For scale: HMRC's Annual Savings Statistics show around 15 million people contributed to an ISA in 2023/24, the highest participation since 2010/11, with cash ISA contributions rising notably over the same period. HMRC publishes this data roughly eighteen months in arrears, so the most recent year available always lags the one you are in.

What changes in April 2027

The overall £20,000 allowance stays where it is, but the way it can be used changes. From 6 April 2027, the amount that can go into a cash ISA is capped at £12,000 for savers under 65, with the remaining £8,000 available only through stocks and shares, innovative finance or a Lifetime ISA. Savers aged 65 and over keep the full £20,000 in cash. The Junior ISA limit of £9,000 is unchanged.

The government has been explicit about the intent: to move money that is sitting in cash toward investment. Whether that is the right move for any individual is a separate question — but 2026/27 is the last full tax year under the current rules, which makes it the last year to use a full £20,000 cash allowance if that is what you want.

The deadline that matters

Midnight on 5 April. Unused allowance is not carried forward, not banked, not recoverable. Each tax year is a separate window that closes completely.

For anyone contributing regularly, the useful habit is a mid-year check — around October — rather than a scramble in the final week, when platform processing times start to matter and transfers can take longer than expected.

Related: ISA vs general investment account explains what sits outside the wrapper — and what that costs.

Sources

• HM Revenue & Customs — Individual Savings Accounts (ISAs), accessed August 2026.
• HM Revenue & Customs — Manage ISA subscriptions for your investors, accessed August 2026.
• HM Treasury — Autumn Budget 2025, accessed August 2026.
• UK Parliament, Treasury Committee — Cash ISA: Government Response, accessed August 2026.
• HM Revenue & Customs — Annual Savings Statistics 2025, accessed August 2026.

Last reviewed: 2 August 2026 · Figures reflect the 2026/27 UK tax year.

This article is general educational information about UK tax and investing rules. It is not personal advice or a recommendation, and it does not take account of your circumstances. Tax treatment depends on individual circumstances and may change. Figures reflect our understanding of the rules for the 2026/27 tax year at the date of publication. If you are unsure, consider speaking to an adviser authorised by the FCA.