UK ISA Calculator
Project UK ISA tax-free growth against the 2026/27 £20,000 annual allowance.
🔒 Runs entirely in your browser — nothing here is ever uploaded
About the UK ISA Calculator
Projects the tax-free growth of a UK Individual Savings Account (ISA) from a current balance and planned annual contributions, capped at the 2026/27 £20,000 annual ISA allowance, and compares it against the same money growing in an ordinary taxable account.
- Enter your current ISA balance and planned annual contribution.
- Enter the number of years to project and an expected annual growth rate.
- Enter a comparison tax rate for the taxable-account comparison.
- Read the projected ISA balance and the tax-free growth advantage.
£15,000 current balance, £10,000/yr contribution, 20 years, 5% growth, comparing against a 20%-taxed account: ISA grows to about £370,459 versus about £330,648 in the taxable account — a roughly £39,811 tax-free growth advantage.
| Period | Allowance |
|---|---|
| 2026/27 (all ISA types combined) | £20,000 |
| From 6 April 2027 — cash ISA (under 65) | £12,000 |
| From 6 April 2027 — stocks & shares ISA | Unaffected (still part of £20,000 total) |
This is a UK-only, GBP-only tool. The taxable-account comparison is a simplification — a flat annual tax on growth, not a precise model of dividend or capital gains tax. Unused ISA allowance does not carry forward; it resets every 6 April. Not financial or tax advice.
- • The £20,000 allowance applies across ALL your ISAs combined, not £20,000 per ISA type.
- • From 6 April 2027, the cash ISA portion of the allowance is due to drop to £12,000 for savers under 65.
- • Unused allowance doesn't carry forward — contributing less than £20,000 in a given year is a permanently lost opportunity for that year.
- gov.uk — Individual Savings Accounts (ISAs) — accessed 2026-08-31
- ii.co.uk — ISA allowance explained: limits and rules for 2026/27 — accessed 2026-08-31
Illustrative estimate only, not financial or tax advice. Verify figures with a licensed adviser or your local tax authority.