ISA Calculator — Tax-Free Savings Growth

Calculate your tax-free ISA savings growth with the £20,000 annual allowance. Compare Cash ISA and Stocks & Shares ISA.

Last updated: April 2026 · Source: GOV.UK

£

Max £1667/month (£20,000/year)

£

ISA Balance after 10 years

£75,599.04

All growth is tax-free

Total Deposits

£60,000.00

Tax-Free Interest

£15,599.04

Tax Saved (vs taxed account)

£3,119.81

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

ISAs shelter savings and investments from all UK income tax and capital gains tax. The annual ISA allowance is £20,000 per tax year, which can be split across Cash ISAs, Stocks and Shares ISAs, Innovative Finance ISAs, and Lifetime ISAs in any combination. Once invested, all interest, dividends, and capital gains within the ISA wrapper are completely tax-free, with no reporting requirement to HMRC.

Cash ISA projections use the stated AER (Annual Equivalent Rate) to calculate growth. A fixed-rate Cash ISA locks your money for 1-5 years at a guaranteed rate, while easy-access ISAs offer flexibility but typically lower rates. The calculation compounds interest annually or monthly depending on the product. For a £20,000 deposit at 4.5% AER over 5 years with annual compounding, the balance reaches £24,931.

Stocks and Shares ISA projections use assumed growth rates since returns are variable. Historical UK equity returns have averaged approximately 7-8% nominal (4-5% real) over the long term, but with significant year-to-year volatility. The calculator models growth at multiple assumed rates and shows the range of outcomes. Platform fees (0.15-0.45%) and fund charges (0.1-1.5%) reduce the effective return and are deducted in the projection.

ISA growth: £20,000/year for 10 years in a Stocks and Shares ISA

  1. Annual contribution: £20,000 (full ISA allowance)
  2. Assumed growth rate: 6% per year after charges
  3. After year 1: £20,000 x 1.06 = £21,200
  4. After 10 years of £20,000 annual contributions at 6%: approximately £279,100
  5. All growth is tax-free — a basic-rate taxpayer saves approx £4,700 in tax vs a general investment account

Source: GOV.UK

Frequently Asked Questions

What does the ISA Calculator — Tax-Free Savings Growth do?
Calculate your tax-free ISA savings growth with the £20,000 annual allowance. Compare Cash ISA and Stocks & Shares ISA. All calculations are performed in your browser using official UK rates and thresholds.
Is this calculator suitable for financial decisions?
This calculator provides estimates for guidance only. Investment returns are not guaranteed and your capital is at risk. Consider seeking independent financial advice before making investment decisions.
Are ISA contributions tax-free?
Yes. The annual ISA allowance for 2025/26 is £20,000. Any interest, dividends or capital gains within an ISA are completely tax-free.