Hundred SummersCapital gains tax calculator: the real band arithmetic
The £3,000 annual exempt amount, then 18% on the slice of gain that fits inside your remaining basic-rate band and 24% above it: gains stack on top of income, which is what flat-rate estimates miss. The same CGT function the Hundred Summers engine uses. Your figures never leave your browser.
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Worked example
Computed when this page was built by the same engine that runs the calculator above, so the figures below and the live tool can never disagree. Change any input above to see your own.
| Inputs | |
|---|---|
| Gain | £20,000 |
| Taxable income | £35,000 |
| Annual exemption left | £3,000 |
| Results | |
|---|---|
| Taxable gain after exemption | £17,000 |
| Capital gains tax | £3,164 |
| Effective rate on the gain | 15.8% |
The next question
What tax is due on the dividends? →Dividend tax calculator
Or answer it with everything else: the full Hundred Summers plan connects your pay, pensions, savings, property, tax and spending year by year, and stress-tests them across 500 simulated market histories.
Read the guides
- Which account to spend first in retirement →ISA, pension, general account: the order you draw them decides how much tax retirement pays. The mechanics of filling the personal allowance, the GIA-first doctrine, and how April 2027 rewrites the classic advice.
- Investment bonds and top-slicing: how a gain is taxed, and when it isn't →Onshore and offshore bonds, the 5% withdrawals that defer tax, chargeable events, and top-slicing relief: the rule that lets a ten-year gain be taxed as if spread over ten years, so a basic-rate taxpayer can pay nothing on an onshore gain.
How gains are actually taxed
CGT is not a flat rate: gains stack on top of your taxable income. Whatever room is left in your basic-rate band (up to £50,270 of taxable income) taxes the gain at 18%; everything above pays 24%. Since 30 October 2024 those rates apply to shares and residential property alike. A low-income year is therefore a genuinely cheaper year to realise gains: retiring soon changes the answer.
The planning levers
The £3,000 exemption resets each tax year and doesn't carry forward: realising gains gradually beats banking them up. Losses offset gains before the exemption applies. Spouse transfers are CGT-free, putting a disposal against two exemptions and two bands. And assets inside ISAs and pensions never pay CGT, which is why the order accounts are drawn down in retirement changes lifetime tax, something the full Hundred Summers plan models year by year (its projections charge CGT on GIA withdrawals and property sales with this same function).