UK Capital Gains Tax Calculator — Methodology

Last verified 5 May 2026 against HMRC Capital Gains Tax guidance. Calculator at /uk/tax/capital-gains-tax-calculator/.

What this calculator does

Estimates Capital Gains Tax on share or residential property disposals using the post-October-2024 unified rates of 18% (basic) and 24% (higher), after deducting the £3,000 annual exempt amount and any allowable costs.

The formula

gain = proceeds - cost - allowableExpenses
taxableGain = max(0, gain - £3,000)

Basic-rate headroom:
  headroom = max(0, £37,700 - taxableIncomeAfterPA)

CGT = min(taxableGain, headroom) × 0.18
    + max(0, taxableGain - headroom) × 0.24

Reporting deadline: 60 days from completion for UK
residential property disposals.

Authoritative sources

• Capital Gains Tax rates
• CGT allowances and reliefs
• Report and pay CGT on UK property
• Autumn Budget 2024 CGT rate changes

Assumptions and limitations

• Applies the unified post-October-2024 rates of 18% / 24% for both shares and residential property.
• Business Asset Disposal Relief (BADR) and Investors' Relief are not modelled.
• Carried interest, crypto-asset specific rules, and chattels exemptions are out of scope.
• Section 104 share pooling and same-day / 30-day matching rules are not applied — supply your own cost basis.
• Private Residence Relief and lettings relief are not modelled.

Source data

The rates used by this calculator are exported as machine-readable CSVs:

• CGT rates 2026/27 /data/cgt-rates-2026-27.csv

These CSVs regenerate automatically from our canonical rate data at every build, ensuring the calculator output and the published rate data stay in sync.

Verification log

• 5 May 2026: CGT rates verified against gov.uk/capital-gains-tax/rates (Autumn Budget 2024 changes)