ISA Calculator
Your ISA wraps your investments in a tax-free bubble. Inside it, dividends and capital gains are never taxed. This calculator shows you exactly what that's worth in pounds over your investment horizon.
Your numbers
£5,000
£0£50,000
£200/mo
£0/mo£1,500/mo
20 yrs
1 yr40 yrs
7%
2%12%
ISA advantage
£13,384
more in your pocket after 20 years by using an ISA
After 20 years
Stocks & Shares ISA£117,738
Zero tax on growth or income
Taxable account (after CGT)£104,353
Includes dividend tax + CGT on disposal
Total contributed
£53,000
Tax saved (est.)
£13,384
Year-by-year
| Year | ISA | Taxable | Difference |
|---|---|---|---|
| 1 | £7,750 | £7,750 | +£0 |
| 5 | £20,815 | £20,806 | +£9 |
| 10 | £42,995 | £42,733 | +£262 |
| 15 | £74,105 | £73,051 | +£1,054 |
| 20 | £117,738 | £114,967 | +£2,771 |
* Taxable column shows pre-CGT value. Final row reflects post-CGT disposal.
Assumptions & notes
- Annual return is split 50/50 between capital growth (deferred until sale) and dividend income (taxed each year above the £500 dividend allowance).
- CGT on the taxable account is calculated at disposal using the £3,000 annual exempt amount (applied once at end, simplified).
- Monthly contributions are added at the start of each year for simplicity.
- Tax rates used: 2025/26 dividend tax rates and post-October 2024 CGT rates.
- This is an illustration only, not financial advice. Past performance does not guarantee future results.