ISA Calculator UK
Project your ISA growth with tax-free compounding. See how regular contributions and investment returns build your savings over time in a Stocks and Shares ISA or Cash ISA.
Inputs
Results
Projected Balance after 20 Years
£221,582
Total Contributions
£125,000
Total Growth
£96,582
Year-by-Year Breakdown
| Year | Contribution | Growth | Balance |
|---|---|---|---|
| 1 | £6,000 | £550 | £11,550 |
| 2 | £6,000 | £878 | £18,428 |
| 3 | £6,000 | £1,221 | £25,649 |
| 4 | £6,000 | £1,582 | £33,231 |
| 5 | £6,000 | £1,962 | £41,193 |
| 6 | £6,000 | £2,360 | £49,553 |
| 7 | £6,000 | £2,778 | £58,330 |
| 8 | £6,000 | £3,217 | £67,547 |
| 9 | £6,000 | £3,677 | £77,224 |
| 10 | £6,000 | £4,161 | £87,385 |
| 11 | £6,000 | £4,669 | £98,054 |
| 12 | £6,000 | £5,203 | £109,257 |
| 13 | £6,000 | £5,763 | £121,020 |
| 14 | £6,000 | £6,351 | £133,371 |
| 15 | £6,000 | £6,969 | £146,340 |
| 16 | £6,000 | £7,617 | £159,957 |
| 17 | £6,000 | £8,298 | £174,254 |
| 18 | £6,000 | £9,013 | £189,267 |
| 19 | £6,000 | £9,763 | £205,030 |
| 20 | £6,000 | £10,552 | £221,582 |
What Is an ISA?
An Individual Savings Account (ISA) is a tax-efficient savings and investment wrapper available to UK residents. Any interest, dividends, or capital gains earned within an ISA are completely tax-free — you never pay income tax or capital gains tax on ISA returns, and you do not need to declare ISA income on your tax return.
ISAs were introduced in 1999 to encourage saving and investing. They have become one of the most popular savings vehicles in the UK, with over 22 million adults holding at least one ISA account.
Types of ISA
There are several types of ISA, each designed for different savings goals:
- Cash ISA — works like a savings account with tax-free interest. Low risk, but returns are typically modest.
- Stocks and Shares ISA — invest in funds, shares, bonds, and other securities with tax-free growth. Higher potential returns but with investment risk.
- Lifetime ISA (LISA) — for adults aged 18-39, with a 25% government bonus on contributions up to £4,000 per year. Can be used for a first home purchase or retirement after 60.
- Innovative Finance ISA — for peer-to-peer lending investments. Higher risk, less commonly used.
This calculator models a general ISA with regular contributions and compound growth, suitable for projecting either a Cash ISA or Stocks and Shares ISA depending on the return rate you enter.
Annual ISA Allowance
For the 2024/25 tax year, the total ISA allowance is £20,000. This is the maximum you can contribute across all your ISAs in a single tax year (April to April). You can split the allowance between different ISA types however you like, but the total cannot exceed £20,000.
The Lifetime ISA has its own sub-limit of £4,000 per year, which counts toward the overall £20,000 allowance. Unused allowance does not carry forward — if you do not use it within the tax year, it is lost.
Tax-Free Growth
The tax-free status of ISAs becomes increasingly valuable over time. Outside an ISA, you would pay income tax on savings interest above your Personal Savings Allowance (£1,000 for basic rate, £500 for higher rate taxpayers), and capital gains tax on investment profits above the £3,000 annual exemption.
Inside an ISA, none of these taxes apply. For a Stocks and Shares ISA with significant growth over many years, the tax savings can amount to thousands of pounds. The longer your money stays invested in an ISA, the greater the benefit of tax-free compounding.
ISA vs Pension
Both ISAs and pensions offer tax advantages, but they work differently. Pension contributions receive tax relief (effectively a government top-up), but you cannot access pension money until age 55 (rising to 57). ISA withdrawals are completely flexible — you can take money out at any time without penalty.
Most financial advisers recommend using both: a pension for long-term retirement savings (especially if your employer matches contributions) and an ISA for medium-term goals or as a flexible complement to your pension. For pension projections, see our Pension Calculator. To track dividend income from your investments, try the Dividend Calculator.
Track Your ISA and All Investments
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