Capital Gains Tax UK Calculator UK CGT estimate. Total gain (£) Annual exemption (£) CGT rate (%) Tax due (£) 3,400 Step-by-step with your numbers: 1. Values used: 2. Total gain = 20,000 £ 3. Annual exemption = 3,000 £ 4. CGT rate = 20 % 5. Tax due = 3,400£ Did we solve your problem today? 👍 Yes 👎 No Thanks for the feedback! Rough UK CGT. Allowances and rates may change. FAQ Residential? Higher rates may apply to property. Related calculators Effective Tax Rate Calculator Find your overall (effective) tax rate. Gross to Net Calculator Find take-home pay after a flat tax/deduction rate. Real Estate Commission Calculator Agent commission.