ISA Calculator
Project the tax-free growth of your Cash, Stocks & Shares, Lifetime or Junior ISA with 2026/27 allowances — including the LISA 25% bonus and the tax you save compared with a taxable account.
Your Savings Plan (2026/27)
Invested at the start, on top of your monthly contributions.
Before inflation. Cash ISA: use the interest rate. Investments: long-run global equity returns have historically averaged roughly 5–8% a year, but are not guaranteed.
Used for the taxable-account comparison — dividends are taxed yearly outside an ISA.
2026/27 allowances: £20,000 overall, £4,000 LISA (within the £20,000), £9,000 Junior ISA. All growth, interest and withdrawals inside an ISA are tax-free.
Results
Projected ISA Value After 10 Years
Entirely tax-free — projection, not a guarantee
You Pay In
Lump sum plus monthly contributions
Growth
Interest / investment returns
Tax Saved vs a Taxable Account
Dividend tax and CGT avoided over 10 years
The same plan outside an ISA
Simplified comparison: allowances and rates held at 2026/27 levels throughout, the whole gain taxed in your selected band, and the CGT exemption used once at sale.
Guide & Information
Overview
Simplify your calculations with our Isa Calculator optimized for United Kingdom users.
💡 Tips
- •Double-check your input values
- •Understand what each field represents
- •Use the results as a starting point for decisions
Why Use This Isa Calculator
Accurate calculations save time and help make better decisions.
Regulations: Complies with current United Kingdom regulations.
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Frequently Asked Questions
How do I use this Isa Calculator?
Simply enter the required values and click calculate. The tool will instantly provide results based on United Kingdom standards.
Can I save my calculations?
You can bookmark this page with your values or take a screenshot of results for future reference.
Is this calculator free to use?
Yes, all our calculators are completely free and available 24/7 for United Kingdom users.
Frequently asked questions
How much can I put in an ISA in 2026/27?
£20,000 across all your adult ISAs (cash, stocks & shares, Lifetime and Innovative Finance combined), of which at most £4,000 can go into a Lifetime ISA. Children have a separate £9,000 Junior ISA allowance. Allowances reset each 6 April and unused allowance cannot be carried forward.
What is changing for cash ISAs from April 2027?
The Autumn Budget 2025 kept the overall allowance at £20,000 but capped new cash ISA contributions at £12,000 a year for savers under 65 from April 2027 — the other £8,000 must go into investment ISAs if you want to use the full allowance. Money already in cash ISAs is unaffected, and the over-65s keep the full £20,000 cash option.
How does the Lifetime ISA bonus work?
You can open a LISA between 18 and 39 and pay in up to £4,000 a year until age 50. The government adds 25% — up to £1,000 a year. Withdrawals are penalty-free only for a first home costing up to £450,000 (after the account is 12 months old) or from age 60; anything else incurs a 25% charge, which removes the bonus plus about 6.25% of your own money.
How much tax does an ISA actually save me?
Outside an ISA, interest above your personal savings allowance (£1,000 basic rate, £500 higher rate, £0 additional rate) is taxed at your marginal rate, dividends above £500 are taxed at 10.75%–39.35% (2026/27), and gains above £3,000 are taxed at 18% or 24% when you sell. Inside an ISA all of that is zero. The saving compounds: this calculator runs your plan both ways and shows the difference.
Is a Stocks & Shares ISA better than a Cash ISA?
They do different jobs. Cash ISAs suit money you may need within roughly five years — the value cannot fall. Stocks & Shares ISAs have historically returned more over long periods but can lose money in any given year. Many savers hold both; note that from April 2027 under-65s can only add £12,000 a year of new money to cash ISAs.
What happens to my ISA money when I withdraw it?
Withdrawals are completely tax-free, whatever the size. With a flexible ISA you can replace withdrawn money in the same tax year without using up more allowance. Two cautions: replacing money in a non-flexible ISA counts as a new contribution, and moving providers should always be done via an ISA transfer — withdrawing and re-depositing loses the tax wrapper.