Capital 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.

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).