ISA vs GIA – Wrapper Choice
Compare the tax efficiency of a Stocks & Shares ISA versus a General Investment Account (GIA). See how much tax you could save with tax-free investing.
Estimates only – not tax advice. For planning purposes only; does not replace professional advice or official HMRC calculations. Full disclaimer
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Multi-Year Projection
Added at the start of each year
Contributions above this go to GIA
Reinvest after-tax dividends in GIA
Crystallise gains yearly vs defer to end
Multi-Year Projection
This projects ISA vs GIA balances over multiple years. Contributions to ISAs are capped at £20,000 per year; any excess goes to the GIA.
The GIA incurs annual dividend tax on income. CGT is deferred until the final year. Over time, the ISA's tax-free compounding creates a growing advantage.
Tax rates used: Dividend allowance £500, CGT allowance £3,000. Rates assumed constant throughout projection.
ISA vs GIA Comparison
Invested
£120,000
Total Growth
+£28,357
Dividend Tax
£0
CGT
£0
Final Balance
£148,357
Invested
£120,000
Total Growth (Gross)
+-£103,711
Dividend Tax
-£0
CGT
-£155
Final Balance
£16,134
ISA Advantage
Over 10 years
Using an ISA for these contributions saves an estimated £154.67 in tax compared with a GIA.
Assumptions used in this calculation (click to expand)
What this calculator assumes
- Annual contribution stays within the £20,000 ISA subscription limit.
- Growth is compounded annually at the rate entered; no intra-year volatility modelled.
- Dividend yield and capital growth split entered are constant across all years.
- GIA dividends use rUK rates after the dividend allowance; CGT applied on realised gains at sale only.
- Taxpayer remains in the same marginal income band across the projection horizon.
Not included in this calculation
- Junior ISAs, LISAs (25% government bonus), or Innovative Finance ISAs.
- Bed-and-ISA mechanics or in-specie transfers.
- Platform fees, fund OCFs, or transaction costs.
- Inflation adjustment (figures are nominal).
- Inheritance tax (ISAs are not IHT-exempt; only AIM-ISAs may qualify for Business Relief).
Statutory basis
ITTOIA 2005 Pt 6 Ch 3 (ISA tax exemption)ITA 2007 ss.13–13A (dividend rates)TCGA 1992 ss.1K–1L (CGT annual exempt amount)
How this is calculated (click to show the formula)
Year-end projection
ISA: Balance × (1 + total return) GIA: Balance × (1 + growth) − dividend tax on yield − CGT on realised gains at exit
The ISA projection compounds gross. The GIA projection withholds dividend tax annually and applies CGT on cumulative gain at the projection endpoint.
Important Notes
This is a simplified projection. It assumes steady returns each year and ignores fee differences, changes in tax rules, behavioural factors, and platform costs.
The calculator does not model 'Bed and ISA' transfers from existing GIA holdings, tax-loss harvesting, or the interaction with other income sources that might affect your marginal tax rate.
ISA allowances are individual; joint investments are not modelled. This tool is for illustration only and is not financial advice.