ISA Calculator
Updated on 22 Oct 2026 for the 2026-27 tax year · Checked by Aotob
Saving £500 a month at 4.5%, your ISA grows to £90,768 in 10 years.
That is £2,448 more than the same savings in a taxed account for a basic rate (20%) taxpayer. You can put in up to £20,000 each tax year.
In your ISA after 10 years
£90,768
Outside an ISA, interest above £1,000 a year is taxed at 20%. The ISA keeps £2,448 more in your pocket.
Show the working
Each month: balance × (1 + 4.5% a year) + 500
Outside an ISA: yearly interest above 1,000 taxed at 20%, 2,220 in total
ISA 90,768 − taxed account 88,320 = 2,448 saved
ISA against a taxed account
Year by year
| Year | Paid in | ISA | Taxed account |
|---|---|---|---|
| 1 | 16,000 | 16,573 | 16,573 |
| 2 | 22,000 | 23,441 | 23,441 |
| 3 | 28,000 | 30,619 | 30,583 |
| 4 | 34,000 | 38,120 | 37,983 |
| 5 | 40,000 | 45,958 | 45,648 |
| 6 | 46,000 | 54,149 | 53,590 |
| 7 | 52,000 | 62,708 | 61,817 |
| 8 | 58,000 | 71,653 | 70,341 |
| 9 | 64,000 | 81,000 | 79,171 |
| 10 | 70,000 | 90,768 | 88,320 |
Questions people ask
How much can I put in an ISA?
£20,000 each tax year (6 April to 5 April), split however you like across cash, stocks and shares, innovative finance and Lifetime ISAs. Up to £4,000 of it can go in a Lifetime ISA.
Do I need an ISA if I have the Personal Savings Allowance?
Basic rate taxpayers get £1,000 of interest a year tax-free and higher rate taxpayers £500, so smaller savings are already untaxed. An ISA matters once your interest goes over that, and it protects growth for every year after.
Is a stocks and shares ISA taxed?
No. Dividends and gains inside any ISA are tax-free, and you don’t report them on a tax return.
Updated 22 Oct 2026Tax year 2026-27Source: HMRC: Individual Savings AccountsChecked by AotobInterest is taxed yearly at your band, above the Personal Savings Allowance. Starting rate for savings not included.Report an issue