UK ISA Calculator (2026-27)
Project the future value of your UK ISA contributions for the 2026-27 tax year — supports Stocks & Shares, Cash and Lifetime ISA with 25% government bonus.
Written by Rahman · Last reviewed
Quick answer
An ISA is a UK tax-free wrapper: no income tax on interest or dividends, no capital gains tax on growth, and no tax to pay when you withdraw. Every UK adult gets a £20,000 allowance per tax year across all ISA types, of which up to £4,000 can go into a Lifetime ISA. The allowance does not carry over — whatever is unused disappears on 6 April.
Tax saved is gains above the £3,000 CGT exemption at 18% — the tax this pot would attract outside an ISA. It is not income tax on the whole gain.
2026-27 limits: £20,000 total ISA allowance (£4,000 of which can go into a Lifetime ISA, which earns a 25% government bonus). A LISA can only be opened between ages 18 and 39, and contributions stop at 50 — so a long projection assumes you are young enough to keep paying in throughout. LISAs are restricted to first-home purchase or age 60+ withdrawals without penalty. All ISA growth and withdrawals are free of UK income tax and capital gains tax. From April 2027, under-65s will be able to put at most £12,000 of the £20,000 allowance into a Cash ISA specifically — the rest must go into Stocks & Shares, Innovative Finance or Lifetime ISAs. That change does not affect the 2026-27 tax year modelled here.
Results are estimates for general guidance and are not financial, tax or legal advice. Except where a calculator names a currency, figures carry no currency of their own — put in pounds and you get pounds back, put in rupees and you get rupees. Figures depend on the assumptions you enter and on rates that change over time — check current rates and speak to a qualified adviser before acting on them.
About the UK ISA Calculator (2026-27)
An ISA (Individual Savings Account) is a UK tax-free savings and investment wrapper. Every UK adult gets a £20,000 annual allowance for the 2026-27 tax year, of which up to £4,000 can go into a Lifetime ISA (LISA) — which adds a 25% government bonus.
All growth, dividends and withdrawals from any ISA are completely free of UK income tax and capital gains tax. This calculator projects how much your ISA could be worth after years of regular contributions and compound growth, accounting for the annual allowance caps.
FV = initial × (1 + r)^n + annual_contrib × ((1 + r)^n − 1) / r
For LISAs, the annual_contrib is multiplied by 1.25 to include the government bonus on contributions up to £4,000.
Investing £500/month (£6,000/year) into a Stocks & Shares ISA over 20 years at a 7% real return: final balance ≈ £254,600. Total contributed: £120,000. Tax-free growth: £134,600. If you held the same in a taxable account and paid basic-rate CGT (18%) on the growth above the £3,000 annual exemption, you'd lose about £23,700 to tax — the ISA wrapper protects all of it.
The allowance does not roll over
The ISA allowance is £20,000 per tax year, and it exists only within that year. Whatever is unused on 5 April is gone — it does not accumulate, and there is no facility to backdate a contribution into a previous year. This is the single most consequential rule in the system and the reason for the rush of subscriptions each March and April.
The allowance is shared across all ISA types rather than applying to each. Putting £20,000 into a stocks and shares ISA leaves nothing for a cash ISA in the same year, whatever the mix.
- Money paid in early in the tax year is sheltered for longer, which over decades is worth more than the same money paid in at the deadline.
- A Lifetime ISA has its own lower cap within the overall allowance, and its own withdrawal restrictions and government bonus.
- Junior ISAs have a separate allowance in the child's name and do not consume the adult one.
Transfer, never withdraw and redeposit
Moving an ISA between providers has one correct method and one expensive mistake. Requesting a transfer through the new provider moves the money while it stays inside the wrapper, and the balance keeps its sheltered status regardless of how large it has grown over the years.
Withdrawing the money and paying it into a new ISA yourself does something entirely different: the withdrawal leaves the wrapper permanently, and paying it back in counts as a fresh subscription against this year's £20,000. A £60,000 balance moved that way cannot be replaced, because only £20,000 of it fits.
- Always initiate a transfer from the receiving provider. Never close the account first.
- Previous years' subscriptions can be transferred in whole or in part; the current year's must generally be transferred in full.
- A flexible ISA is the exception — it permits withdrawal and replacement within the same tax year without consuming allowance — but not every provider offers the feature, and it does not apply across tax years.
Allowances and ISA rules are set by HMRC and change; the figures here are for the 2026/27 tax year and this calculator is refreshed annually. One change is already confirmed: from April 2027, under-65s will only be able to put up to £12,000 of the £20,000 allowance into a Cash ISA specifically — the rest must go into Stocks & Shares, Innovative Finance or Lifetime ISAs. That does not affect the 2026/27 year modelled here.
2026-27 UK ISA allowance breakdown
| ISA type | Annual limit | Government bonus | Use case |
|---|---|---|---|
| Stocks & Shares ISA | £20,000 | None | Long-term investing in funds, shares, bonds |
| Cash ISA | £20,000 | None | Tax-free savings (lower returns, no investment risk) |
| Lifetime ISA | £4,000 | 25% (up to £1,000/yr) | First home or retirement at 60+ (penalty for other withdrawals) |
| Junior ISA | £9,000 | None | For under-18s; locked until age 18 |
The £20,000 total allowance covers all ISA types combined — you can split it however you like, but no more than £4,000 of that £20,000 can go into a LISA.
Frequently Asked Questions
What does "tax-free" mean for ISAs?
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No UK income tax on interest or dividends, and no capital gains tax on profits when you sell. The funds are funded with already-taxed income (it's not a pension), but everything inside grows and comes out tax-free.
What is the Lifetime ISA bonus?
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The government adds 25% on top of every contribution up to £4,000/year — so £4,000 becomes £5,000. You must be 18-39 to open one, contributions only until age 50, and withdrawals before age 60 are penalised 25% (unless used to buy a first home up to £450,000).
Can I split £20,000 across multiple ISAs?
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Yes — since 2024 you can pay into multiple ISAs of the same type in one tax year, as long as total contributions don't exceed £20,000. The LISA sub-limit of £4,000 still applies.
What happens to unused allowance?
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It does not roll over. Use it or lose it — each 6 April starts a fresh £20,000 allowance and the previous year's unused capacity is gone.
Are ISAs better than pensions?
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Different tools. Pensions give upfront tax relief and lock the money until 55+ (rising to 57). ISAs use already-taxed money but offer total flexibility — withdraw any time, no tax owed. Most UK savers use both.
Sources
- GOV.UK — Individual Savings Accounts (ISAs) — Official £20,000 annual ISA allowance for the 2026-27 tax year.