ISA Calculator 2026/27: Tax-Free Savings
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Calculate how your ISA grows over time with compound returns. Enter your annual contribution (up to the £20,000 allowance), expected return, and time horizon to see your tax-free balance, total contributed, and total growth. Withdrawals from most ISAs are also completely tax-free.
ISA Details
All growth and withdrawals are completely free of UK income tax and capital gains tax. The ISA allowance is £20,000 per tax year (2026/27).
Assumes contributions made at the start of each year, compounded annually. Returns are not guaranteed. Stocks and Shares ISA returns can go up or down. Past performance is not indicative of future results. Does not constitute financial advice.
How ISA Growth Works
An Individual Savings Account (ISA) is a tax-efficient wrapper. Money inside an ISA grows completely free of UK income tax and capital gains tax, no matter how large the pot becomes. The annual allowance of £20,000 is the maximum you can contribute per tax year across all your ISAs combined.
The power of ISAs comes from compound growth: returns on your investments generate further returns over time. This calculator compounds annually, meaning each year's return is added to the balance before the next year's calculation. A Stocks and Shares ISA invested at a long-run average of 6-7% per year can grow substantially over decades.
For comparison: the same amount saved outside an ISA in a savings account would have interest taxed as income, and any investment gains outside an ISA above the annual capital gains tax exempt amount (£3,000 in 2026/27) would be taxable. Over 20 or 30 years, the tax saving can be very significant.
ISA Types at a Glance (2026/27)
| ISA Type | Annual Limit | Best For |
|---|---|---|
| Cash ISA | £20,000 | Emergency fund, short-term savings |
| Stocks and Shares ISA | £20,000 | Long-term growth (5+ years) |
| Lifetime ISA (LISA) | £4,000 | First home purchase or retirement |
| Innovative Finance ISA | £20,000 | Peer-to-peer lending |
| Combined annual limit | £20,000 | Per person per tax year |
The LISA allowance (£4,000) counts towards the overall £20,000 annual limit.
| Years | Total Contributed | Tax-Free Balance | Tax-Free Growth |
|---|---|---|---|
| 5 | £100,000 | £112,746 | £12,746 |
| 10 | £200,000 | £263,616 | £63,616 |
| 15 | £300,000 | £465,902 | £165,902 |
| 20 | £400,000 | £735,855 | £335,855 |
| 30 | £600,000 | £1,581,636 | £981,636 |
The annual ISA allowance for 2026/27 is £20,000 per person. This can be split across different types of ISA in the same tax year: Cash ISA, Stocks and Shares ISA, Innovative Finance ISA, and Lifetime ISA (limited to £4,000 of the total allowance). Unused allowance cannot be carried forward to the next tax year.
A Cash ISA works like a savings account: you earn interest on your deposit, and all interest is free of income tax. A Stocks and Shares ISA lets you invest in funds, shares, bonds, and other assets; any growth and dividends within the ISA are free of income tax and capital gains tax. Cash ISAs offer lower but more predictable returns; Stocks and Shares ISAs have higher long-term growth potential but carry investment risk.
Yes, from most ISAs. Cash ISAs and Stocks and Shares ISAs allow withdrawals at any time, though you lose the withdrawn allowance (you cannot put it back unless you have a flexible ISA). Lifetime ISAs have restrictions: withdrawals before age 60 for non-property-purchase purposes incur a 25% government withdrawal charge, which effectively returns the bonus plus a penalty. Always check your ISA terms before withdrawing.
This calculator uses annual compound growth, assuming contributions are made at the start of each year and grow at your chosen rate. The formula is: balance = sum of (contribution x (1 + rate)^remaining years). In practice, monthly contributions to a Stocks and Shares ISA would compound more frequently, and returns fluctuate year to year. The calculator gives a useful planning estimate, not a guaranteed outcome.
A Lifetime ISA allows UK residents aged 18-39 to save up to £4,000 per year, receiving a 25% government bonus (up to £1,000 per year). The LISA can be used to buy your first home (property up to £450,000) or to fund retirement from age 60. Withdrawals for other purposes before age 60 incur a 25% government charge, which effectively claws back the bonus plus 6.25% of your own money. LISAs count towards your £20,000 ISA allowance.