ISA vs GIA — When Your Investments Are Taxed and When They’re Not

The difference between a Stocks and Shares ISA and a General Investment Account is the single most important tax distinction for UK investors. Getting it wrong — or just not thinking about it — costs people real money every year.

ISA: the tax-free wrapper

Inside an ISA, you pay:

No Capital Gains Tax on profits from selling investments.
No income tax on dividends.
No tax on interest.

There’s no reporting to HMRC either. ISA investments don’t appear on your self-assessment. According to HMRC’s ISA guidance, you can invest up to £20,000 per tax year across all your ISA types combined.

The tax exemption has no upper limit on gains. If you put £20,000 into an ISA and it grows to £200,000 over a decade, the entire £180,000 gain is tax-free. There’s no point at which the gains become taxable.

GIA: taxable by default

A General Investment Account has no tax wrapper. Gains from selling investments are subject to CGT under the normal rules — share matching, current rates (18%/24%), and the £3,000 annual exemption.

Dividends above £500 are taxed at 8.75%/33.75%/39.35%. Interest above your Personal Savings Allowance is taxed at your marginal rate.

You also have reporting obligations — if disposal proceeds exceed £12,000 or gains exceed £3,000, you must file SA108.

Why do people use GIAs at all?

There are legitimate reasons:

You’ve used your £20,000 ISA allowance. If you’re investing more than £20,000 a year, the excess has to go somewhere. That’s the GIA.

You want access to assets ISAs can’t hold. Some securities, certain foreign shares, and some derivative products aren’t eligible for ISAs. Options trading (on Robinhood UK or Tastytrade) can’t be done inside an ISA.

You’re building up to transfer into an ISA. The “bed and ISA” strategy involves holding in a GIA temporarily, then selling and rebuying inside the ISA wrapper.

The annual ISA maths

Consider what a £20,000 annual ISA contribution saves you over time:

Over 20 years, you’d save over £100,000 in CGT simply by using your ISA allowance. That’s not even counting the dividend tax savings. As the FCA’s Financial Lives survey has repeatedly shown, most people aren’t using their full ISA allowance — which means they’re paying tax they don’t need to.

Moving from GIA to ISA

If you already have investments in a GIA, you can’t just “transfer” them into an ISA — you have to sell and rebuy. Some brokers (like Trading 212) offer a streamlined “move to ISA” feature, but under the hood it’s still a sell and repurchase.

The sell triggers a CGT disposal. If you have gains, use your £3,000 annual exemption. If the gain exceeds the exemption, you’ll pay some CGT — but the future growth is then permanently tax-free. It’s almost always worth it. Our bed and ISA guide walks through the strategy in detail.

What about mixing ISA and GIA trades?

If you hold the same stock in both your ISA and your GIA, they’re treated as completely separate holdings. The ISA shares don’t interact with your GIA’s Section 104 pool. This is confirmed in HS284.

The most common mistake people make: accidentally including ISA trades in their CGT calculation. If your broker’s CSV export includes both ISA and GIA transactions (as Freetrade’s does), filter out the ISA rows before calculating.

TaxBull auto-detects ISA transactions from brokers that label them and excludes them from the CGT calculation. For brokers that don’t distinguish, make sure you’re only uploading your GIA history.

This is general information only. ISA rules are set by HMRC and can change. Check gov.uk/individual-savings-accounts for the latest.