ISA Growth Calculator
Type your monthly contribution and target years. UK ISA allowance is £20,000/year for 2026/27.
Updated May 2026, using HMRC 2026/27 rates and current ONS / gov.uk figures.
An ISA (Individual Savings Account) shelters all gains and dividends from UK tax. Annual contribution allowance: £20,000 for adults, £9,000 Junior ISA, £4,000 LISA (counts toward main ISA limit).
How it works. Future value of ordinary annuity, monthly compounding. Assumes constant rate — real returns will vary.
Worked examples
£300/mo (£3,600/yr) at 5% for 30 years: ~£250,000
£1,667/mo (£20k/yr) at 6% for 25 years: ~£1,160,000 — ISA millionaire territory.
£500/mo at 4% for 40 years: ~£600,000
Sources:
HMRC ISA rules
· retrieved 2026-05-12.
Frequently asked questions
What's the ISA allowance?
£20,000 per tax year for adults in 2026/27. Frozen for several years — the real-terms allowance has fallen with inflation.
Can I have multiple ISAs?
From 2024/25 you can pay into multiple of the same type (e.g. two cash ISAs) within the £20,000 total allowance.
Are LISA contributions on top of ISA allowance?
No. LISA (£4,000/yr) counts toward the £20,000 overall ISA allowance.