ISA Growth Calculator
Our free ISA calculator projects the tax-free growth of your ISA savings over any time horizon — showing final balance, total contributions, and total tax-free interest or growth earned. ISAs are one of the most powerful savings tools available in the UK, and understanding their long-term potential is the first step to making the most of your annual £20,000 allowance.
ISA Growth Calculator
Project how much your ISA could grow over time — all interest and returns are tax-free.
ISA Types and 2026/27 Allowances
Every UK adult can save up to £20,000 per tax year across all ISA types combined. The main options are: a Cash ISA (best rates currently 4.5–5% AER) for easy-access or fixed-term tax-free interest; a Stocks and Shares ISA for tax-free investment in funds, shares, and bonds with higher long-term growth potential; a Lifetime ISA (LISA) for first-time buyers or retirement saving, offering a 25% government bonus on up to £4,000 per year; and a Innovative Finance ISA for peer-to-peer lending (higher risk).
Junior ISAs allow parents to save up to £9,000 per year tax-free on behalf of a child, accessible when they turn 18. The child cannot access the funds until maturity, making JISAs an excellent long-term savings discipline.
The Long-Term ISA Advantage
Maximising the annual ISA allowance for 20 years at a 5% annual return produces a pot of approximately £685,000 — compared with approximately £600,000 in a taxable account for a higher rate taxpayer, after income tax on interest. The difference of £85,000 represents the tax saving from the ISA wrapper alone. For Stocks and Shares ISA investors, the capital gains tax saving can be even larger as the pot grows beyond the CGT annual exemption.
Building an ISA habit — even contributing just £500 per month — produces significant tax-free wealth over time. Use our Savings Calculator to compare ISA growth with taxable savings at the same rate.
Frequently Asked Questions
From April 2024, you can open and contribute to multiple ISAs of the same type in the same tax year — previously restricted to one of each type. The total annual contribution across all ISAs remains capped at £20,000.
Exceeding the annual ISA allowance is penalised by HMRC — the excess contribution and any income or gains on it may be taxed at your marginal rate, and you may receive a penalty. Your ISA provider and HMRC both track contributions, so it is difficult to over-contribute without detection.
Flexible ISAs allow withdrawals and replacements within the same tax year without using additional allowance. Not all ISAs are flexible — check the terms of your specific account. A standard ISA does not allow replacement of withdrawn funds above the annual allowance.
A LISA is worth it if you are saving for a first home worth £450,000 or less, or for retirement after age 60. The 25% government bonus is exceptional value — a £4,000 annual contribution becomes £5,000. However, a 25% withdrawal penalty applies to non-qualifying withdrawals (calculated on the full withdrawal amount, not just the bonus), which effectively means you lose more than the bonus if you cash out early for non-qualifying purposes.
For money you will need within 5 years, a Cash ISA is lower risk and appropriate. For long-term goals (10+ years), a Stocks and Shares ISA has historically outperformed cash over the long term, though with greater volatility. Many investors use both — cash for shorter-term goals, stocks and shares for longer. Our Investment Calculator models long-term growth at various equity return assumptions.
Enter your annual ISA contribution and the expected annual return. The ISA allowance for 2026/27 is £20,000. All growth inside an ISA is tax-free indefinitely — you never pay income tax on interest or capital gains tax on investment growth, regardless of how large the pot becomes. For a Cash ISA, use the current AER; for a Stocks and Shares ISA, a planning assumption of 5-7% per annum is commonly used, though actual returns are not guaranteed. The calculator shows the projected balance year by year. Note that unused ISA allowance cannot be carried forward to future tax years — each year’s £20,000 is use-it-or-lose-it. Also note that contributing to a Lifetime ISA counts toward the overall £20,000 limit.
Important Information
This calculator is provided for general information and planning purposes only. It does not constitute financial or tax advice and should not be relied upon as such. Figures are indicative estimates based on simplified, publicly available criteria and stated assumptions. Actual results depend on your full circumstances. See our Disclaimer for further information.