Engine 08 • Wealth Optimiser
UK Tax Year 2026/27 Verified

Tax Drag & ISA vs. GIA Optimiser

Analyse the compounding friction of Capital Gains Tax and Dividend Tax in a General Investment Account (GIA) versus tax-sheltered wrappers like ISAs under UK tax legislation.

00. Engine Configuration
01. Portfolio Profile
£
£1,000
20 Yrs
02. Market Assumptions
7.0%
2.0%
03. UK Tax Parameters
15%
£500 Dividend Allowance & £3,000 CGT Exemption per year.
ISA Wrapper Valuation
£0
100% Tax-Free Compound Growth
GIA Valuation (Taxed)
£0
After Annual Taxes & CGT Liquidation
Total Tax Drag Friction
£0
Capital Lost to Tax: 0%
Wealth Trajectory: ISA vs. GIA
Long-Term Wealth Breakdown
Total Out-of-Pocket Contributions £0
ISA Contribution Limit Flag Within Annual Allowance
ISA Net Investment Gain £0
GIA Net Investment Gain £0
Cumulative Dividend & Annual Tax Paid £0
Final CGT Charge On Full Liquidation £0
Total Wealth Preserved by ISA £0
Assumptions & Engine Methodology

The Mechanics of Tax Drag

Outside of tax wrappers, portfolio compounding is dampened by two annual leakage points: Dividend Tax on cash flows and Capital Gains Tax (CGT) on rebalancing sales. Slicing off even small percentages annually compounds into substantial performance friction over multi-decade horizons.

UK Tax Rules Applied (2026/27)

Taxes are calculated using standard UK tax rates. When enabled, annual tax allowances are applied dynamically:

  • Dividend Allowance: £500 per tax year tax-free.
  • CGT Annual Exempt Amount: £3,000 per tax year exempt from realised gains.
  • Annual ISA Limit: £20,000 per individual per tax year.

Model Simplifications & Computational Notes

Monthly compounding applies dividend yields and capital returns smoothly across the year. Annual dividend and CGT allowances are evaluated once per year. On final liquidation, the £3,000 annual CGT allowance is applied against remaining unrealised gains as a single-year exit event.

Disclaimer: This tool provides illustrative mathematical models based on current UK tax legislation for educational purposes only. It does not constitute financial or tax advice. Tax rates and individual allowances are subject to change by legislative bodies.