Project the tax-free growth of an ISA from a starting balance plus monthly contributions. The 2026/27 ISA allowance is 20,000 - everything inside an ISA grows free of UK income tax and Capital Gains Tax.
Your ISA
£
£
%
yrs
Projected ISA value
£169,950
All growth is tax-free
Total paid in£100,000
Tax-free growth£69,950
Final ISA value£169,950
Inside an ISA there’s no income tax, dividend tax or Capital Gains Tax on your returns — and nothing to declare on a tax return.
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Why ISAs are powerful
An ISA (Individual Savings Account) shelters your money from UK tax: no income tax on interest, no tax on dividends, and no Capital Gains Tax on growth. You can pay in up to 20,000 across your ISAs each tax year (2026/27). Over years, sheltering returns from tax can add up to a substantial difference versus an unwrapped account.
Annual allowance: 20,000 (2026/27), resetting each 6 April.
Types include Cash ISA, Stocks & Shares ISA, Lifetime ISA (4,000 limit, within the 20,000) and Innovative Finance ISA.
Growth and withdrawals are tax-free and do not need to go on a tax return.
Worked example
10,000 starting balance + 500/month for 15 years at 6%.
Total paid in = 100,000.
Projected value about 170,000 - entirely free of UK tax inside the ISA.
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Frequently asked questions
What is the ISA allowance for 2026/27?
20,000 per person across all your ISAs in the tax year. A Lifetime ISA has its own 4,000 cap which counts within the overall 20,000.
Cash ISA or Stocks & Shares ISA?
Cash ISAs suit short-term goals and emergency money where you cannot risk losses. Stocks & Shares ISAs suit longer horizons (typically 5+ years) where you are comfortable with ups and downs for potentially higher returns. This calculator works for either - just choose a suitable rate.
Report a bug or ask a question about this calculator
Important: BrickCrunch provides general information and estimates only — this is not financial, tax, mortgage or legal advice. Calculations are simplified and your circumstances may differ. UK tax and rate figures are checked against gov.uk (21 June 2026 (2026/27 tax year)) but rates change and errors are possible. Always confirm figures with gov.uk or a qualified professional before making decisions.
