UK ISA Calculator
Project the tax-free growth of your ISA contributions up to the £20,000 annual allowance. Free, privacy-first — inputs never leave your browser.
Details
Result
ISA Value
£232,176
Total Contributed
£120,000
Tax-Free Gains
£112,176
Tax Saved (vs GIA)
£22,435
For estimation only. Not professional financial, tax, or legal advice. Consult a qualified advisor before making decisions. Full disclaimer.
What is an ISA?
An ISA (Individual Savings Account) shelters up to £20,000/year of savings or investments from UK Income Tax and Capital Gains Tax. Returns compound tax-free — crucial over 10-30 year horizons where CGT would otherwise eat 10-20% of gains.
Cash ISA vs Stocks & Shares ISA
Cash ISAs are safe but lag inflation. Stocks & Shares ISAs are volatile year-to-year but historically return 7-9% p.a. over the long term. Use Cash for short-term goals (<5 years) and S&S for long-term wealth building.
Common questions about ISA
What is the ISA annual allowance?+
£20,000 per tax year (6 April – 5 April). Can be split across Cash ISA, Stocks & Shares ISA, Lifetime ISA (£4k), and Innovative Finance ISA. All gains and withdrawals are tax-free.
Cash ISA vs Stocks & Shares ISA?+
Cash ISA: safe, but returns may lag inflation (4-5% in 2026). Stocks & Shares ISA: volatile but historical 7-9% real returns over 10+ years. Horizon under 5 years → Cash. Longer → Stocks.
What is a Lifetime ISA (LISA)?+
For ages 18-39, contribute up to £4,000/year and receive a 25% government bonus (£1,000 max) until age 50. Can be used for: (a) first home purchase up to £450,000, or (b) retirement at age 60+. Early withdrawal for any other reason: 25% penalty (effectively losing the bonus plus a bit of your own money). The £4k LISA counts toward the £20k total ISA allowance. Powerful for first-time home buyers with 5+ year horizons.
Can I transfer ISAs between providers?+
Yes. Use a formal ISA transfer form with the new provider — never withdraw and redeposit, which would use new allowance. You can transfer current-year contributions (must be complete transfer) and any prior-year ISAs (partial or complete). Cash to Stocks & Shares ISA (or vice versa) is allowed and preserves tax-free status. Transfer times: 15 working days for Cash to Cash; 30 for Stocks & Shares. Top platforms (Vanguard, Hargreaves Lansdown, Fidelity) handle transfers smoothly.
What happens to ISAs when I die?+
Pre-6-April-2018: ISA status ended at death; spouse got "Additional Permitted Subscription" (APS) one-off allowance equal to deceased's ISA value. Post-April-2018: ISA becomes a "continuing ISA" retaining tax-free status until the estate is settled, up to 3 years. Spouse's APS allowance is still available. ISA assets pass to beneficiaries via the Will/intestacy, potentially subject to Inheritance Tax (unless going to spouse, which is IHT-exempt).
Does a Flexible ISA let me replace withdrawals?+
Yes — many Cash ISAs and some Stocks & Shares ISAs are designated "flexible". You can withdraw money and replace it within the same tax year without it counting against your £20,000 allowance. Example: deposit £20k in May 2026, withdraw £5k in August, replace £5k by 5 April 2027 — allowance intact. Lifetime ISA and Junior ISA cannot be flexible. Always confirm flexibility with your provider before moving large sums; non-flexible ISAs permanently lose any allowance associated with withdrawn funds.