ISA vs GIA Calculator
See how much tax a Stocks and Shares ISA saves you compared with the same investments in a taxable general investment account (GIA), including UK dividend tax and capital gains tax.
1What you invest
£
Added at the end of each month in both accounts.
£
Optional. Money already available to invest on day one, for example an existing GIA balance you are weighing up.
yr
2Expected returns
% / yr
% / yr
The part of the total return paid out as dividends and reinvested. The remaining 5% is price growth.
3Your tax situation
£
Your income before dividends (salary, pension, profits). It positions dividends and gains in the UK tax bands, including the personal allowance taper.
At this income your marginal rates are 35.75% on dividends and 24% on gains.
Who invests
Tax year rules
Dividend allowance: £500 per year. CGT annual exempt amount: £3,000.
Sale at the end
After 20 years
+£35,833
Extra after-tax wealth the ISA wrapper leaves you with after 20 years, compared with holding the same investments in a taxable account.
Stocks & Shares ISATax-free
£253,768 after tax
Total contributed£120,000Investment growth£133,768Tax paid£0
Taxable account (GIA)
£217,936 after tax
Value before CGT£239,114Dividend tax paid−£10,483CGT at sale−£21,178
ISAGIA after tax
£264k
£198k
£132k
£66k
£0
Now4y8y12y16y20y
After tax, the taxable account compounds at 5.65% per year versus 7% in the ISA: a tax drag of 1.35% per year.
Gross dividends received in the GIA£38,353
Dividend tax paid (above the £500 yearly allowance)−£10,483
Taxable gain when sold at the end£91,244
Capital gains tax at sale (£3,000 exempt amount per sale year)−£21,178
Total ISA advantage£35,833
Of the total advantage, £10,483 is dividend tax and £21,178 is capital gains tax. The remaining £4,171 is lost compounding: growth the taxable account never earned on the money that left the pot as dividend tax each year.
Embed this calculator Updated: July 2026 · 2026/27 rates
How to
How to use the ISA vs GIA calculator
1
Enter your monthly investment and horizon
Set an optional starting lump sum, how much you invest each month and for how many years. The calculator runs the identical plan twice: once inside a Stocks and Shares ISA and once in a taxable general investment account.
2
Split the return into growth and dividends
Enter the total annual return you expect and how much of it arrives as dividends. The split matters: dividends are taxed every year in a GIA, while price growth is only taxed once, when you sell.
3
Enter your income and how you invest
Your taxable income positions dividends and gains in the UK bands exactly (10.75%, 35.75% or 39.35% on dividends in 2026/27; 18% or 24% CGT), including the personal allowance taper. Couple mode doubles every allowance, and you can spread the final sale over several tax years.
4
Read the tax saved and the two curves
The headline figure is the extra after-tax wealth the ISA leaves you with. The chart shows both accounts over time, with the GIA valued after all dividend tax and the CGT due if you sold that year.
Concepts
ISA vs GIA: allowances, dividend tax and CGT explained
What is a Stocks and Shares ISA?
An Individual Savings Account is a tax wrapper: investments held inside it pay no UK dividend tax and no capital gains tax, and withdrawals are tax-free too. You can add up to £20,000 per tax year across all your ISAs. Nothing inside an ISA needs to be reported on a tax return.
What is a GIA?
A general investment account is a standard taxable brokerage account with no contribution limits and no tax protection. Dividends above the dividend allowance are taxed every year, and selling at a profit can trigger capital gains tax. GIAs are typically used once the ISA allowance is full.
The £20,000 ISA allowance
Each tax year (6 April to 5 April) you can pay up to £20,000 into ISAs in total. The allowance does not roll over: whatever you don’t use by 5 April is gone. That is £1,666.67 per month, the threshold this calculator flags when your monthly amount exceeds it.
Dividend tax and the £500 allowance
In a GIA, the first £500 of dividends each year is tax-free. Above that, dividends are taxed by income tax band: 10.75% (basic), 35.75% (higher) and 39.35% (additional) in 2026/27, after the basic and higher rates rose by 2 percentage points in April 2026. Inside an ISA the rate is always zero.
Capital gains tax on shares
When you sell investments in a GIA at a profit, gains above the £3,000 annual exempt amount are taxed at 18% (basic rate) or 24% (higher and additional rate). The exempt amount was £12,300 as recently as 2022/23; its shrinking has made the ISA wrapper far more valuable than it used to be.
Tax drag on compounding
Dividend tax in a GIA does not just cost the tax itself: every pound paid in tax stops compounding for all the remaining years. Over long horizons this lost growth often becomes the biggest slice of the ISA’s advantage, which is why the gap between the two curves widens faster and faster.
Bed and ISA
Bed and ISA means selling investments in your GIA and immediately rebuying them inside your ISA. The sale can use your CGT exempt amount, and everything moved is sheltered from then on. Most UK platforms offer it as a single transaction; it is the standard way to migrate an existing GIA.
Which account should you fill first?
For most UK investors the order is: employer pension match first, then the ISA up to £20,000, and only then a GIA. A workplace or personal pension can beat the ISA on tax relief, but the ISA wins on flexibility: you can withdraw any amount at any age, tax-free.
Tips
How to keep more of your returns
Fill the ISA before the GIA
Same funds, same platform, same returns: the only difference is the wrapper. Until you invest more than £20,000 per year, there is rarely a good reason to hold long-term investments in a taxable account.
Use both partners’ allowances
Married couples and civil partners can shelter £40,000 per year between them, and assets can be transferred between partners tax-free to use both CGT exempt amounts and both dividend allowances.
Bed and ISA your existing GIA
Each year, sell enough GIA holdings to use your £3,000 CGT exempt amount and rebuy them inside the ISA. Over a few Aprils an entire taxable portfolio can migrate into the wrapper at little or no tax cost.
Mind the April deadline
The ISA allowance resets on 6 April and unused allowance is lost forever. If cash is available late in the tax year, contributing before 5 April preserves an allowance you cannot get back later.
Keep income-heavy assets wrapped
If you hold both wrapped and unwrapped investments, put the high-yield ones (dividend shares, bond funds, REITs) inside the ISA first. They generate taxable income every year in a GIA, while low-yield growth assets defer most of their tax to the final sale.
Don’t let the tax tail wag the dog
The wrapper decides how much you keep, not how much you earn. Pick the investments first, then the account. And remember this tool models UK rules only: it is a planning aid, not personal tax advice.
FAQ
What is the difference between an ISA and a GIA?+
Both can hold the same funds and shares. An ISA is a tax wrapper: no dividend tax, no capital gains tax and no tax on withdrawals, but contributions are capped at £20,000 per tax year. A GIA has no limits and no tax protection: dividends and realised gains above the allowances are taxed.
How much is the ISA allowance in 2026/27?+
It is £20,000 per person, unchanged since 2017. It covers all ISA types together (cash, stocks and shares, innovative finance and Lifetime ISA, the last capped at £4,000 within the total). From April 2027 the government plans to cap the cash portion at £12,000 for under-65s, with the overall £20,000 limit unchanged.
How are dividends taxed in a GIA in 2026/27?+
The first £500 of dividends each year is tax-free. Above that you pay 10.75% as a basic rate taxpayer, 35.75% at higher rate and 39.35% at additional rate. The basic and higher dividend rates rose by 2 percentage points in April 2026.
How much capital gains tax will I pay when I sell?+
Gains above the £3,000 annual exempt amount are taxed at 18% within your remaining basic rate band and 24% above it. This calculator stacks the gain on top of your income and that year’s dividends, so a large single sale is automatically split across both rates, and spreading the sale over several years uses several exempt amounts.
Is an ISA worth it for small monthly amounts?+
Yes, mostly because of time. £200 per month stays under the allowances for a while, but as the pot grows, dividends exceed £500 per year and gains exceed £3,000 well before typical horizons end. Opening the wrapper early costs nothing and protects the whole future pot.
Can I move existing GIA investments into my ISA?+
Not directly: you must sell in the GIA and rebuy inside the ISA, a process called Bed and ISA. The sale is a disposal for CGT, so most investors move up to £3,000 of gains each year to stay within the exempt amount. The rebuy uses ISA allowance like any other contribution.
Do I pay tax when I withdraw money from an ISA?+
No. ISA withdrawals are completely tax-free at any age, do not count as income and never appear on a tax return. With a flexible ISA you can even replace withdrawn money within the same tax year without using new allowance.
What if I want to invest more than £20,000 a year?+
The overflow goes into a GIA (this calculator flags when your monthly amount exceeds the allowance), into a partner’s unused ISA allowance, or into a pension, which has its own annual allowance of up to £60,000 and adds tax relief on contributions.
Does the calculator include platform fees and fund charges?+
No. Fees usually apply equally to both wrappers on the same platform, so they barely change the comparison. Enter a return net of charges if you want the projection itself to be more realistic; the ISA-vs-GIA gap is driven by tax, not fees.
What assumptions does this calculator make?+
Same investments in both accounts, dividends reinvested monthly, dividend tax paid from the account at each year end, allowances not used elsewhere, and rates frozen at the selected tax year’s values. Dividends and gains are stacked on top of your entered income to find the exact band, couple mode assumes an equal split and equal incomes, and during a phased sale the cash proceeds stop growing in both accounts. It is a comparison tool, not tax advice.
Both accounts invest the same starting lump sum and monthly amount at the same total return, split into price growth and dividend yield and compounded monthly with dividends reinvested. The ISA pays no tax. In the GIA, each tax year’s dividends are stacked on top of your taxable income and taxed with HMRC’s rules for the selected year: personal allowance (£12,570, tapered above £100,000), the £500 dividend allowance as a nil rate band, then 10.75% in the basic band, 35.75% in the higher band and 39.35% above £125,140 (2026/27); the tax is paid from the account at year end. At the end of the plan both accounts are moved to cash, all at once or in equal yearly steps: each GIA sale realises the pool’s average cost gain, deducts the £3,000 annual exempt amount per sale year, and taxes the rest at 18% within your remaining basic rate band and 24% above it. Couple mode assumes an equal split and equal incomes and doubles every allowance. Fees, inflation, loss harvesting and future rate changes are ignored. The ISA advantage is the ISA value minus the after-tax GIA value; the yearly tax drag compares the two accounts’ effective annual returns.
GOV.UK: Tax on dividends · Capital Gains Tax rates and allowances · Individual Savings Accounts · illustrative, not tax advice