ISA Calculator UK — Tax-Free Savings & Investment Returns
Estimate how much your ISA could be worth with our free UK ISA calculator. Choose between a Cash ISA or Stocks and Shares ISA, enter your initial lump sum, monthly contributions, expected growth rate and time period. The calculator shows your projected balance, total contributions, interest or growth earned, and how much you save in tax compared to a standard taxable account.
ISAs (Individual Savings Accounts) are one of the most tax-efficient ways to save and invest in the UK. Every adult has an annual ISA allowance of £20,000, and all interest, dividends and capital gains within an ISA are completely tax-free. For a higher-rate taxpayer investing £500 per month over 20 years, the tax savings alone can exceed £15,000. Whether you are building an emergency fund in a Cash ISA or investing for the long term in a Stocks and Shares ISA, this calculator helps you see the power of tax-free compounding.
Understanding ISAs and the Annual Allowance
Individual Savings Accounts (ISAs) were introduced in 1999 to encourage saving among UK residents. The annual ISA allowance for 2025/26 is £20,000, which can be split across Cash ISAs, Stocks and Shares ISAs, Innovative Finance ISAs and Lifetime ISAs in any combination. Since April 2024, you can open multiple ISAs of the same type in a single tax year, giving you more flexibility than ever. All income and gains within an ISA are free from income tax and capital gains tax.
The tax advantage of ISAs becomes more valuable as your savings grow. A higher-rate taxpayer earning 5% on £50,000 in a standard savings account would owe £1,000 in tax each year. In an ISA, that £1,000 stays invested and compounds further. Over 20 years, the tax saved and reinvested can add tens of thousands of pounds to your total wealth. For full details on ISA rules and allowances, visit the GOV.UK ISA page.
Cash ISA vs Stocks and Shares ISA
Cash ISAs work like standard savings accounts but with tax-free interest. They are ideal for short-term savings goals (under 5 years) or emergency funds where capital preservation is paramount. Current Cash ISA rates range from 3% to 5% depending on the provider and whether you choose easy access or fixed-term. Stocks and Shares ISAs invest your money in funds, shares, bonds or investment trusts. They carry the risk of short-term losses but historically deliver higher long-term returns of 7 to 10% annually before inflation.
For most people, a combination of both works well: a Cash ISA for your emergency fund and near-term goals, and a Stocks and Shares ISA for long-term wealth building. To model how your contributions might grow at different rates, try our compound interest calculator. If you are also saving for retirement, our pension calculator shows how workplace pensions with employer matching and tax relief compare to ISA investing.
The Lifetime ISA for First-Time Buyers and Retirement
The Lifetime ISA (LISA) is available to anyone aged 18 to 39. You can save up to £4,000 per year and receive a 25% government bonus of up to £1,000 annually. The funds can be used towards your first home (up to £450,000) or withdrawn tax-free after age 60 for retirement. Withdrawing for any other reason incurs a 25% penalty, which actually results in a net loss on your original contributions, so the LISA is best suited for people with a clear goal of buying their first home or supplementing their pension.
Yes. Since April 2024 you can open multiple ISAs of the same type, as long as total contributions stay within £20,000.
Cash ISA: fixed/variable interest, no capital risk. Stocks & Shares ISA: invested in funds/shares/bonds, potentially higher returns but value can fall.
Cash ISAs: FSCS protected up to £85,000 per institution. Stocks & Shares ISAs: FSCS covered if provider fails, but not against market losses.
Yes, anytime. Standard ISAs do not restore your allowance. Flexible ISAs let you replace withdrawals within the same tax year.
The ISA loses tax-free status from the date of death. A surviving spouse/civil partner can inherit the tax benefits via the Additional Permitted Subscription allowance.
This calculator provides estimates for guidance only. Returns are not guaranteed. The value of investments can fall as well as rise. This is not financial advice. Tax treatment depends on individual circumstances and may change. For regulated financial advice, speak to a qualified financial adviser.