Capital Gains Tax Calculator · Methodology

How the calculation works

Estimate UK Capital Gains Tax for one disposal under 2026/27 standard rates, show how the gain is reduced, and compare selling a divisible holding in one tax year with phasing equal gains across several tax years.

Return to calculator

Included

Shares and funds held outside tax wrappers
Cryptoassets, residential property and other assets using the standard rates
Acquisition, buying, selling and capital-improvement costs
User-entered reliefs and current-year allowable losses
Other taxable gains and taxable income
The annual exempt amount
The 18% and 24% rate split
After-tax profit and sale proceeds
An equal-gain comparison across two to five tax years for divisible holdings

Outside this method

ISA and pension investments
Share identification, same-day and 30-day matching rules
Private Residence Relief and other relief calculations
Brought-forward loss ordering
Joint ownership and transfers between spouses or civil partners
Non-residence, temporary non-residence and foreign tax
Business Asset Disposal Relief, investors’ relief and carried interest
Trusts, estates, companies and partnership interests
Tax advice, filing or a determination that a disposal is legally feasible

Calculation

Core formulas

Disposal gain

Gain = sale proceeds − acquisition cost − allowable buying, selling and improvement costs

A negative result is treated as a capital loss; user-entered reliefs reduce only a positive gain.

Net gains before exemption

Net gains = this disposal’s relieved gain + other gains − current-year allowable losses

The model applies current-year losses before the annual exempt amount.

Taxable gain

Taxable gain = max(0, net gains − annual exempt amount)

The exemption is limited to the positive gains left after losses.

Rate allocation

18% slice = min(taxable gain, basic-rate band − taxable income); 24% slice = remainder

Taxable income is assumed to use the basic-rate band before taxable capital gains.

Disposal’s tax effect

CGT with this disposal − CGT on other entered gains alone

This isolates the change in estimated tax created by the disposal, including any tax reduction produced by a loss.

Phased-disposal comparison

Annual asset gain = relieved gain ÷ selected tax years

Each equal slice uses that year’s annual exemption and remaining basic-rate capacity under the stated assumptions.

Timing convention

When cash flows occur

The sell-now calculation combines the entered disposal, other gains and current-year losses in one tax year. The phased comparison assigns other gains and losses only to year one, uses the entered current taxable income in year one and the future taxable-income assumption in every later year. It holds the 2026/27 exemption, bands and rates unchanged.

Limitations

What the result cannot establish

The calculator cannot identify which acquisition cost applies where pooling or statutory asset-matching rules are relevant.
The relief input relies entirely on the user having established eligibility and amount.
Current-year losses and brought-forward losses follow different ordering rules; only current-year losses are modelled.
Spreading is an illustration for divisible holdings, not a statement that a sale can be divided or that doing so is advisable.
Market prices, income, costs, gains, losses, allowances and tax rates may change between years.
Property disposals can have Private Residence Relief and a 60-day reporting deadline that materially affect the result.
Other reporting obligations can arise even where the estimate shows no tax due.

Reference tests

Numerical checks

Case	Inputs	Expected result
GOV.UK basic-rate example	£20,000 taxable income; £12,600 gains; £3,000 exemption; no losses	£1,728 CGT
GOV.UK mixed-rate example	£20,000 taxable income; £52,600 gains; £3,000 exemption; no losses	£10,842 CGT
Allowable disposal costs	£50,000 acquisition; £100,000 proceeds; £500 buying and £500 selling costs	£49,000 gain before reliefs and losses
Higher-rate taxpayer	£50,000 taxable income; £10,000 gains; £3,000 exemption	£1,680 CGT
Capital loss	£50,000 acquisition; £40,000 proceeds; no costs or other gains	£10,000 loss and £0 CGT
Two-year phasing	£50,000 taxable income; £20,000 gain; £3,000 annual exemption; two equal tax years	£4,080 now versus £3,360 phased; £720 modelled saving

Evidence

Sources

GOV.UK — Capital Gains Tax rates and allowances GOV.UK — Capital Gains Tax tax-free allowances GOV.UK — Work out if you need to pay Capital Gains Tax GOV.UK — Work out your gain on property GOV.UK — Using capital losses GOV.UK — Reporting and paying Capital Gains Tax