What is an ISA (Individual Savings Account)?
An ISA (Individual Savings Account) is a UK tax-free savings and investment wrapper that lets each adult shelter up to GBP 20,000 of new contributions per tax year. All interest, dividends, capital gains, and withdrawals inside an ISA are completely free of UK income tax and CGT, at any age.
Detailed definition
ISAs were launched on 6 April 1999 by Gordon Brown's Treasury to replace the older PEP (Personal Equity Plan, 1986) and TESSA (Tax-Exempt Special Savings Account, 1991) regimes. The wrapper is administered by HMRC, but the accounts themselves are held with banks, building societies, fund platforms, robo-advisers, and peer-to-peer lenders. There is no tax to pay on income or gains inside an ISA, no Self Assessment reporting requirement, and no lifetime contribution cap, only the annual GBP 20,000 subscription limit.
The annual allowance has been GBP 20,000 since 6 April 2017 and is frozen there until at least April 2030 under current Treasury policy. The 2024/25 ISA reforms removed two long-standing restrictions: the one-of-each-type-per-tax-year rule (you can now open and contribute to two Cash ISAs in the same year), and the partial-transfer restriction (you can now transfer part of a current-year subscription without moving the whole thing).
The four wrappers serve different goals. Cash ISAs hold deposit savings and pay interest, taxed at 0 percent versus the standard Personal Savings Allowance of GBP 1,000 (basic) or GBP 500 (higher) outside an ISA. Stocks and Shares ISAs hold funds, ETFs, individual equities, bonds, and investment trusts. Innovative Finance ISAs hold peer-to-peer loans (a niche market since the FCA tightened P2P rules in 2019). Lifetime ISAs target under-40s saving for a first home or retirement and add a 25 percent government bonus on up to GBP 4,000 per year.
How it works
Total ISA subscription limit 2026/27 = GBP 20,000 per adult Lifetime ISA sub-cap = GBP 4,000 (counts toward GBP 20,000) Junior ISA (under-18) separate limit = GBP 9,000 Cash ISA tax on interest = 0 percent S and S ISA tax on dividends / CGT = 0 percent Outside ISA: dividend allowance = GBP 500, then 8.75 / 33.75 / 39.35 percent Outside ISA: CGT annual exempt amount = GBP 3,000, then 18 / 24 percent
- Eligibility: UK resident, aged 18 plus (16 plus for Cash, 18 to 39 for new LISAs).
- Allowance reset: 6 April each year. Unused allowance does NOT roll over.
- Withdrawals: tax-free at any age; LISA penalty 25 percent for non-eligible withdrawals before 60.
- Transfers preserve the wrapper across years. Always use the receiving provider's transfer form.
- Inheritance: a surviving spouse or civil partner receives an Additional Permitted Subscription (APS) equal to the deceased's ISA value, on top of their own GBP 20,000.
Worked example
Compare two 35-year-old basic-rate taxpayers in 2026/27, each contributing GBP 10,000 per year for 20 years into a low-cost global equity tracker returning 6 percent per year. One uses a Stocks and Shares ISA, the other a regular General Investment Account (GIA).
| Metric | Stocks and Shares ISA | General Investment Account |
|---|---|---|
| Total contributed over 20 years | GBP 200,000 | GBP 200,000 |
| Pot at year 20 (6 percent compounded) | GBP 389,927 | ~GBP 360,000 (after dividend tax drag) |
| Tax on dividends each year | GBP 0 | 8.75 percent above GBP 500 allowance |
| CGT on the GBP 189,927 gain at sale | GBP 0 | (189,927 - 3,000) x 18 percent = GBP 33,647 |
| Net pot in your hand | GBP 389,927 | ~GBP 326,000 |
ISA vs SIPP
The two main UK long-term tax wrappers solve different problems. An ISA is the better choice for flexible, pre-retirement saving. A SIPP is the better choice for retirement-only money where you want upfront tax relief.
| Feature | ISA | SIPP |
|---|---|---|
| Annual contribution cap | GBP 20,000 | GBP 60,000 (or 100 percent of earnings if lower) |
| Upfront tax relief | None | 20 / 40 / 45 percent (basic / higher / additional) |
| Tax on growth | 0 percent | 0 percent |
| Withdrawal age | Any age | 57 from 2028 (currently 55) |
| Tax on withdrawals | 0 percent on all amounts | 25 percent tax-free, rest taxed as income |
| Best for | Pre-retirement flexibility, basic-rate payers, large pots already used by pension annual allowance | Higher and additional rate payers, employer matching, hard pre-retirement spending discipline |
Common pitfalls
- Withdrawing and re-depositing in a non-flexible ISA. This burns fresh allowance instead of using the existing wrapper. Always check whether your provider offers a flexible ISA, and always use a formal transfer for between-provider moves.
- Not using the allowance before 5 April. Unused allowance is lost forever; it does not carry over.
- Holding too much in Cash ISAs at younger ages. With CPI averaging 3 percent and Cash ISA rates often below this, the real value of a long-term cash holding shrinks. Stocks and Shares ISAs historically beat inflation over 10 plus years.
- Forgetting the LISA penalty. A 25 percent penalty on non-eligible withdrawals returns less than your original contribution (penalty is on full balance, not just the bonus).
- Sterling cash drag inside a Stocks and Shares ISA. Uninvested cash earns near-zero on most platforms; check the cash rate or sweep into a money-market fund.
Related terms
Related calculators on 3Tej
Model contributions, growth, and tax savings across ISAs, SIPPs, and the full UK tax stack:
Frequently asked questions
What is the 2026/27 ISA allowance?
The annual ISA subscription allowance is GBP 20,000 per adult for the 2026/27 UK tax year (6 April 2026 to 5 April 2027), unchanged since 2017/18. Within that GBP 20,000 a Lifetime ISA is capped at GBP 4,000, and a Junior ISA for under-18s carries its own separate GBP 9,000 limit.
Can I open multiple ISAs of the same type in one tax year?
Yes. From 6 April 2024 onwards you can subscribe to multiple ISAs of the same type (for example two Cash ISAs and two Stocks and Shares ISAs) in the same tax year, as long as your total subscriptions stay within the GBP 20,000 overall limit. The old one-of-each-type-per-year rule was abolished in the 2024/25 reforms and remains scrapped for 2026/27.
What is the difference between an ISA and a SIPP?
An ISA gives no upfront tax relief but all withdrawals are tax-free at any age. A SIPP gives 20 to 45 percent income tax relief on contributions but locks the money up to age 57 (rising to 58 in 2028), then taxes 75 percent of the pot as income on the way out. Higher and additional rate taxpayers usually prefer SIPPs for the bigger upfront relief; basic-rate payers and anyone who wants flexibility before 57 prefer ISAs.
Are ISA withdrawals tax-free?
Yes. Withdrawals from a Cash, Stocks and Shares, or Innovative Finance ISA are completely free of UK income tax, dividend tax, and capital gains tax, and they do not need to be reported on a Self Assessment return. Lifetime ISA withdrawals before age 60 for anything other than a first-home purchase carry a 25 percent government penalty, which removes the bonus and a small slice of your own contributions.
What is a flexible ISA and why does it matter?
A flexible ISA lets you withdraw money and replace it within the same tax year without using fresh allowance. For example, withdraw GBP 5,000 in June and pay it back by 5 April and the GBP 5,000 still counts as already-subscribed, not new subscription. Cash ISAs are commonly flexible; Stocks and Shares ISAs may not be. Check the provider's literature: flexibility is at the provider's discretion, not a statutory feature.
How do I transfer an ISA between providers?
Always use the new provider's transfer form, never withdraw and re-deposit. A transfer preserves the tax-free wrapper across all years of past subscriptions; a withdraw-and-redeposit treats it as fresh subscription and burns this year's allowance. Cash to Cash, Cash to S and S, and S and S to S and S transfers must complete within 15 working days for current-year money or 30 days for prior years.
Sources and further reading
- HMRC (2026) Individual Savings Accounts (ISAs), gov.uk - official subscription limits and rules.
- HMRC (2024) ISA reforms 2024/25, gov.uk - multiple-of-same-type rule changes.
- HMRC (2026) Lifetime ISA, gov.uk - LISA bonus rules and withdrawal penalty.
- FCA (2024) Consumer investments data review - statistics on ISA usage.
- MoneySavingExpert (2026) Best Cash ISAs - current rates comparison.