UK ISA Allowance & Returns Calculator

ISA Guide 2026/27

What do I need to know about ISA Types and Allowances 2026/27?

Annual ISA allowance: £20,000 per person per tax year (unchanged since 2017/18). Types: Cash ISA — deposit account, FSCS protected, currently 4.5-5.0% AER for best buys. Stocks and Shares ISA — invest in funds, shares, investment trusts, ETFs. Junior ISA — £9,000 allowance per child per year. Lifetime ISA — up to £4,000/year with 25% government bonus (max £1,000/year bonus), for first home purchase or retirement (from age 60). Help to Buy ISA (closed to new applicants 2019). All ISA income and growth is entirely tax-free, regardless of which type or combination of ISAs you hold.

What's the difference between Cash ISA and Stocks and Shares ISA?

Cash ISA: protected up to FSCS limits to capital, returns currently 4.5-5.0% AER (best buy easy access 2024). Returns taxable outside ISA wrapper. Stocks and Shares ISA: historical long-term average returns approximately 7-10% per year (for a globally diversified index fund). Volatile in the short term — falls of 30-50% can occur. For money needed within 5 years: Cash ISA (capital security matters). For money not needed for 5+ years: Stocks and Shares ISA typically produces significantly higher long-term returns than cash, despite short-term volatility along the way.

What's the key thing to understand about The Lifetime ISA (LISA)?

LISA key rules: must open between ages 18-39. Contribute up to £4,000/year. Government adds 25% bonus (up to £1,000/year). Use for: first home purchase (property up to £450,000) or retirement (access from age 60). Penalty for other withdrawals: 25% charge on the whole withdrawal, which recovers the bonus and a portion of your own contributions (effectively a 6.25% exit penalty on your own money). For first-time buyers: the LISA beats the Help to Save for property up to £450,000 because the 25% bonus effectively boosts every pound saved by a quarter, on top of whatever investment growth the account achieves.

What should I know about Maximising Your ISA?

Key strategies: use your full allowance each year if possible — unused allowance cannot be carried forward. Use the full £20,000 at the start of the tax year (6 April) to maximise the full year's growth. Couple: £40,000/year combined allowance — maximise both. Children: £9,000/year Junior ISA — investing from birth is powerful. HMRC's new rules (effective 2024): multiple Cash ISAs are now permitted in the same tax year (previously only one of each type per year). Transfers: you can transfer between ISA providers or between ISA types without it counting against your annual allowance, as long as it's a proper ISA-to-ISA transfer rather than withdrawing and re-depositing the cash yourself.

You Can Split the Allowance, But the Total Is a Hard Cap

The annual ISA allowance is a single combined limit that can be split across different ISA types in any tax year — for example, part in a cash ISA and part in a stocks and shares ISA — but the sum across all of them can never exceed the overall annual limit, regardless of how many separate ISA accounts or providers you use. Since the 2024 rule change allowing multiple ISAs of the same type to be opened and funded within a single tax year, the key constraint to track isn't "how many accounts" but simply "how much total has gone in across everything" against the single annual ceiling, which this calculator is built to track for exactly that reason.

Why Unused Allowance Never Rolls Forward

Unlike pension carry-forward rules, the ISA allowance is strictly use-it-or-lose-it each tax year: any portion not contributed by the deadline is gone permanently and cannot be added to a future year's allowance. This makes the final weeks before the tax year-end deadline a common rush period for savers trying to "top up" before losing that year's allowance entirely, and it's also why financial advisers often recommend contributing early in the tax year rather than waiting, both to capture a full year of potential tax-free growth and to avoid the risk of missing the deadline altogether due to processing times near the cut-off.

Inheriting ISAs: The Additional Permitted Subscription for Spouses

When an ISA holder dies, their spouse or civil partner can benefit from a rule that doesn't apply to any other ISA scenario: the Additional Permitted Subscription (APS). The APS gives the surviving spouse an extra ISA allowance equal to the value of the deceased's ISA at the point of death, on top of their own normal annual allowance, so the tax-advantaged status of that money isn't lost on transfer. This differs from simply inheriting the cash or investments as part of the estate, which would otherwise mean the funds lose their ISA wrapper and any future growth becomes taxable. The APS can generally be used with the same ISA provider the deceased held the account with, or in some cases a different provider that accepts APS transfers, and it must usually be used within a set window after the estate is settled or the account closed. For couples with substantial combined ISA holdings, understanding the APS matters for estate and tax planning, since without claiming it, a surviving spouse inheriting a large ISA could otherwise only shelter it from future tax using their own standard annual allowance, spread over several years.

ISA Allowance Usage Scenarios (Reference Table)

The £20,000 annual ISA allowance can be split across different ISA types in the same tax year, as long as the combined total across all of them does not exceed the overall cap. The Lifetime ISA has its own separate £4,000 sub-limit that counts toward, not on top of, the main allowance.

Worked Example: Maximising a £20,000 Allowance With a LISA Bonus Suppose a 28-year-old saving for a first home puts the maximum £4,000 into a Lifetime ISA. The government adds a 25% bonus on LISA contributions, worth £4,000 x 25% = £1,000 in this case, paid directly into the account (subject to the usual LISA rules on eligible withdrawals). The remaining £16,000 of the £20,000 allowance goes into a Cash ISA, using up the full annual allowance. The combined effect is £20,000 of personal deposits plus a £1,000 government bonus, meaning £21,000 has been added to tax-free savings for an outlay of £20,000 — a return that's hard to beat anywhere else, provided the LISA funds are eventually used for an eligible first home purchase or after age 60, since early withdrawal for other reasons carries a 25% government charge that can leave you with less than you paid in.

What Happens If You Accidentally Exceed the Allowance

Occasionally someone opens more than one ISA of the same type in a tax year, or miscounts contributions across providers, and ends up depositing more than the £20,000 annual allowance in total. HMRC does track ISA subscriptions across providers via data each ISA manager reports, and an over-subscription is usually identified automatically rather than requiring the saver to notice it themselves — HMRC typically writes to the saver explaining the breach and, in most cases, instructs one of the ISA providers to remove the excess amount (plus any growth on it) and treat it as if it were never an ISA subscription, meaning any interest or gains on the excess portion become taxable in the ordinary way. The saver doesn't usually face a direct penalty for a genuine, accidental breach, but the administrative correction can take months to resolve and the excess funds lose their ISA tax-free status for the period involved. The most common cause is subscribing to two Cash ISAs, or two Stocks and Shares ISAs, with different providers in the same tax year without realising only one of each type (plus one Innovative Finance ISA and the Lifetime ISA) is normally allowed per tax year — always check a provider's rules and keep a simple running total of what's gone into each ISA type before opening a new one mid-year.