ISA Calculator 2026/27
Understanding your ISA projection
The calculator above projects growth from your annual contribution, your current balance and an assumed annual return. The results are an illustration, not a forecast: real returns vary year to year, and a Stocks & Shares ISA can fall as well as rise, particularly over short periods. The 7% figure suggested for a Stocks & Shares ISA is a long-run average before charges, and the 4% to 5% figure for a Cash ISA is the sort of rate seen in recent years rather than a guarantee.
Worked examples over 10 years
The table assumes a contribution at the end of each year, no starting balance, and a constant return. Real accounts compound more frequently and returns are uneven, so the figures are only a guide.
| Contribution | Return | Total paid in | Value after 10 years | Tax-free growth |
|---|---|---|---|---|
| £5,000 a year | 7% | £50,000 | £69,082 | £19,082 |
| £10,000 a year | 7% | £100,000 | £138,164 | £38,164 |
| £20,000 a year | 7% | £200,000 | £276,329 | £76,329 |
| £20,000 a year | 6% | £200,000 | £263,616 | £63,616 |
| £20,000 a year | 4.5% | £200,000 | £245,764 | £45,764 |
The gap between the 7% and 6% rows for a £20,000 yearly contribution is £12,713 over ten years. That is roughly what a 1% annual charge would cost, which is why platform and fund fees matter as much as the return you assume. Compare the total cost of a platform, including fund charges and any custody or dealing fees, not just the headline fee.
The main ISA rules for 2026/27
The annual ISA allowance is £20,000 per person, which you can split across Cash, Stocks & Shares, Innovative Finance and Lifetime ISAs. Contributions to a Lifetime ISA count towards the £20,000, and the Lifetime ISA limit is £4,000 a year, which earns a 25% government bonus worth up to £1,000. You can open a Lifetime ISA between 18 and 39 and pay in until age 50. Withdrawals are allowed for a first home costing up to £450,000, from age 60, or if you are terminally ill; otherwise a 25% charge applies, which takes back the bonus and a little of your own money. The allowance resets each 6 April and unused allowance cannot be carried forward.
The government has announced that the annual cash ISA limit will be reduced for under-65s from April 2027, so check GOV.UK for the current position before planning large cash contributions.
Why ISAs matter for tax
Interest, dividends and capital gains inside an ISA are free of tax, and you do not have to report them on a tax return. Outside an ISA, savings interest above the Personal Savings Allowance (£1,000 for basic-rate taxpayers, £500 for higher-rate and nothing for additional-rate) is taxable, the dividend allowance is only £500, and the Capital Gains Tax annual exempt amount is £3,000. With allowances this small, a growing investment portfolio can reach taxable territory sooner than people expect, and an ISA is a simple way to shelter it.
Choosing between Cash, Stocks & Shares and Lifetime ISAs
A Cash ISA suits money you may need within a few years, and deposits are covered by the Financial Services Compensation Scheme up to £120,000 per person per institution. A Stocks & Shares ISA suits money you can leave invested for five years or more, accepting that the value will move up and down. A Lifetime ISA suits first-home buyers and long-term retirement saving, but the withdrawal charge makes it a poor home for money you might need for other purposes. Many people use more than one type for different goals.
You can transfer existing ISA money between providers without losing the tax-free status, as long as you use the provider's transfer process rather than withdrawing and re-depositing. Pension contributions are the other main tax-free route: see our pension calculator to compare, and our Lifetime ISA calculator for the bonus. This page gives general information and is not financial advice; consider speaking to a regulated adviser for decisions about your own savings.
Sources: GOV.UK: Individual Savings Accounts and GOV.UK: Lifetime ISA.