Capital Gains Tax calculator
Figures Last checked Where these come from
On £45,000 of income and a £30,000 gain, Capital Gains Tax is £6,164. Not one rate but two: after the £3,000 allowance, £5,270 of the gain still fits inside the basic rate band and is charged at 18%, while £21,730 sits above it at 24% — an effective 20.55% of the gain.
How this is worked out
GOV.UK sets out the method in four steps: work out your taxable income, work out your total gains, take the Annual Exempt Amount off the gains, and add what is left to your taxable income. Whatever part then falls inside the basic Income Tax band is charged at 18%, and anything above it at 24%.
That stacking is the whole difficulty, and it is why "are you a higher rate taxpayer?" is the wrong question. Your income uses the basic rate band first; the gain gets whatever room is left. A basic rate taxpayer with a large gain pays both rates on it, and someone whose income already fills the band pays the higher rate on all of it. The tax on an unchanged gain therefore rises with your salary — and not in proportion to it.
Taxable income here is worked out by the same engine the take-home pay calculator uses, so the personal allowance taper above £100,000 is applied: a larger income means a smaller allowance, more taxable income, and less room for the gain. Doing that subtraction by hand is how a calculator quietly disagrees with itself.
Checked against HMRC's own examples
GOV.UK publishes two worked examples on its Capital Gains Tax rates page, and both are reproduced as tests against this engine. The second is the one that matters: taxable income of £20,000 and gains of £52,600, which GOV.UK works through as 18% on £17,700 and 24% on £31,900, for £10,842. Every intermediate figure is asserted, not just the total — a calculator can reach the right answer through the wrong split, and the split is what this page shows you.
What catches people out
- Capital Gains Tax is not charged at "your rate". Your gain is stacked on top of your taxable income, and whatever part of it still fits inside the basic rate band is charged at 18% while the rest is charged at 24%. One gain is routinely taxed at both, which is why a calculator that asks whether you are a higher rate taxpayer and applies a single figure is wrong in both directions.
- The Annual Exempt Amount is £3,000 and it is use-it-or-lose-it. It does not roll forward, it is per person rather than per asset, and a couple who jointly own an asset each have their own — which is why the timing of a disposal, and whose name an asset is in, change the bill more than the rate does.
- Capital Gains Tax is not devolved. GOV.UK quotes one basic rate band, £37,700, for the whole UK, so a Scottish taxpayer whose income tax bands are quite different still crosses into the 24% CGT rate at the same point as everyone else. Working it out from Scottish bands overstates the tax.
- These are the rates for ordinary assets. Trustees and personal representatives pay a flat 24%, and gains qualifying for Business Asset Disposal Relief are charged at 18% — but that relief has eligibility conditions no calculator can assess, so this page does not pretend to. You do not usually pay Capital Gains Tax on your main home at all.
- The figure to enter is the gain, not the sale price. The gain is what you sold for minus what you paid and minus allowable costs, and losses — in this year or carried forward from earlier ones — come off before the allowance does. Entering a sale price instead of a gain overstates the tax enormously.
Questions
How much can I make before paying Capital Gains Tax?
£3,000 of gains in the tax year. Above that the excess is taxable, at 18% for the part that fits inside your remaining basic rate band and 24% for anything beyond it.
The allowance is per person, so a jointly owned asset has two. It does not carry forward — an unused allowance is simply gone at the end of the tax year.
Why does my salary change my Capital Gains Tax?
Because the gain is added on top of your taxable income to decide which rate applies to it. Income uses up the basic rate band first, and the gain is charged at 18% only for whatever room is left.
So the same gain costs more the more you earn — and not proportionally. On GOV.UK's own example, £10,000 more income turns £600 of a gain from 18% into 24%.
Do I pay Capital Gains Tax when I sell my house?
Usually not. Your main home is normally covered by Private Residence Relief, and GOV.UK says plainly that you do not usually pay tax when you sell your home.
It can apply if you let the property out, used part of it for business, or it is very large. A second property or a buy-to-let is chargeable in the ordinary way.
What about shares in an ISA?
No Capital Gains Tax at all. Gains inside an ISA or PEP are exempt, as are UK government gilts, Premium Bonds and betting or lottery winnings.
Shares held outside a tax-free wrapper are chargeable, which is the single biggest practical difference between the two ways of holding the same investment.
When do I have to report and pay it?
It depends on the asset. Gains on UK residential property have their own short reporting deadline, separate from Self Assessment, and missing it carries penalties.
Other gains are normally reported through Self Assessment. GOV.UK's reporting guidance sets out which applies — this page works out how much, not when.
Sources
What your income alone costs in tax
Work out the next thing
- Stamp dutyAll three UK regimes — SDLT, LBTT and LTT — with first-time buyer relief where it exists, and the same price compared across England, Scotland and Wales.
- Dividend taxDividends stacked on your income and split across the bands — with the allowance treated as a nil-rate band rather than a deduction, which is where most tools go wrong.
- Mortgage overpaymentWhat paying extra actually buys: years off the term and interest avoided.