ISA Calculator UK (2026)
Estimate tax-free ISA compound growth from annual contributions, years, and expected investment returns.
United Kingdom Calculator
Adjust Your Inputs
Move the sliders or type exact numbers. Results update instantly.
Instant Estimate
Your Results
Estimated ISA Value
£473,498
Based on your selected isa calculator assumptions. Try different sliders to compare scenarios.
Total Contributions
£250,000
Investment Growth
£223,498
These calculations are financial projections and planning estimates, not tax, legal or licensed financial advice. HMRC 2025/2026 statutory rates, NI thresholds, and local council rates apply.
How to Use the ISA Calculator
Enter starting ISA balance
Input your existing Stocks & Shares or Cash ISA savings.
Set annual contribution
Enter your planned yearly contribution (up to the statutory £20,000 annual allowance).
Project investment horizon and return
Set investment duration and expected average annualized return (typically 6-9%).
Formula & Calculation Methodology
Future Value = Contributions compounded tax-freeThis calculator uses standard United Kingdom financial formulas, IRS thresholds, and amortization schedules. All results compute instantly in your browser with zero data stored or transmitted.
Calculation Examples & Scenarios
Maxing the £20,000 Allowance (10 Years)
£20,000 yearly contribution (£1,666/month), 7% annual compound growth.
Steady £500/Month Savings (20 Years)
£6,000 yearly contribution over 20 years at 7% return.
Key Benefits
- 100% exempt from UK Capital Gains Tax (CGT) and UK Dividend Tax forever
- No HMRC reporting required on annual Self Assessment tax returns
- Enforces the statutory £20,000 annual ISA allowance limit across Cash and Stocks & Shares
Common Use Cases
- Wealth builders evaluating the compounding power of Stocks & Shares ISAs
- High earners sheltering dividend portfolios from rising dividend tax rates
- Retirees planning tax-free bridge income prior to accessing state or workplace pensions
Why the UK ISA Allowance is the Most Powerful Wealth Shelter
Every UK resident aged 18 or older receives an annual ISA allowance of £20,000. Any capital gains, interest, or dividend income generated within an ISA wrapper is completely immune to UK taxation. Unlike pensions, funds inside an ISA can be withdrawn at any time without income tax deductions or early withdrawal penalties.
Frequently Asked Questions
The statutory annual ISA allowance is £20,000 per tax year for UK residents aged 18 and older. You can split this £20,000 across multiple Cash ISAs, Stocks & Shares ISAs, Innovative Finance ISAs, or up to £4,000 in a Lifetime ISA.
Yes. All interest, capital gains, and dividend income generated inside an Individual Savings Account (ISA) wrapper are completely exempt from UK income tax, capital gains tax, and dividend tax forever.
Historically, a diversified global equity portfolio (such as an MSCI World or S&P 500 index fund) has returned an annualized 7% to 9% before inflation over 10 to 20-year investment periods.
Yes. You can transfer existing ISA balances between cash and investments at any time using the official ISA transfer service without consuming your current year’s £20,000 annual allowance.
UK residents aged 18 to 39 can contribute up to £4,000 per year into a Lifetime ISA and receive an instant 25% government bonus (up to £1,000/year) toward buying a first home (under £450k) or retirement at age 60.
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