See how your investment portfolio grows over time with regular contributions and compound returns.
UK investment growth inside a Stocks & Shares ISA is fully tax-free on dividends, interest, and capital gains. The 2026/27 S&S ISA allowance is £20,000. Historic UK equity returns (FTSE All-Share since 1900) have averaged approximately 5% real and 7-8% nominal, with material decade-to-decade variation.
A UK Stocks & Shares ISA is the most tax-efficient general-purpose investment account available to retail investors in the world for amounts under £20,000/year. Compared with a US taxable brokerage (which pays tax on dividends annually and capital gains on realisation), or many European equivalents (which may carry wealth-tax exposure), the UK S&S ISA is a sealed tax-free wrapper that holds whatever ETFs, funds, shares, or bonds you put in it.
Allowance: £20,000/year across all ISA types combined (Cash, S&S, Lifetime, Innovative Finance). The Junior ISA adds £9,000/year for under-18s. Allowances do not roll over — use it or lose it each tax year, which ends 5 April.
Investment options inside an S&S ISA: - UK and global equity index funds (typical OCF 0.05-0.30%) - Active managed funds (typical OCF 0.50-1.50%) - Individual shares (UK + most major international markets via your broker) - Investment trusts - ETFs (UCITS-compliant; most US-domiciled ETFs are not eligible for retail UK investors post-PRIIPs) - Bonds and gilts
Realistic return assumptions: - UK equities (FTSE All-Share, since 1900): ~5% real, ~7-8% nominal - Global equities (MSCI World, since 1970): ~6% real, ~9% nominal - UK gilts: ~1-2% real, ~4-5% nominal - 60/40 global blend: ~3-4% real, ~6% nominal
Cost drag (often underweighted): - Platform fee: 0.15-0.45% on most retail platforms - Fund OCF: 0.05-1.50% - Trading costs (active management): 0.10-0.50% - Cumulative 1% per year cost drag reduces a 40-year terminal balance by approximately 25%
The calculator outputs nominal terminal value, real terminal value (CPI-adjusted), total contributions vs growth, and year-by-year drawdown sustainability at a chosen withdrawal rate. For ISA rules, HMRC's ISA Manager Reference Manual and the gov.uk ISA pages are authoritative; the ONS CPI series is the standard inflation reference.
See how your investment portfolio grows over time with regular contributions and compound returns.
The Rule of 72 gives a quick estimate: 72 ÷ annual return = years to double. At a 7% real return, money doubles roughly every 10 years. With a $500 monthly contribution and 7% real growth, a $10,000 starting balance grows to about $250,000 over 20 years and $830,000 over 35 years.
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