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What The Capital Gains Tax Calculator Works Out
- Taxable gain: the gain less the GBP 3,000 annual exempt amount (if you have not already used it this year). The exempt amount has shrunk from GBP 12,300 in 2022/23 to GBP 3,000, pulling far more ordinary investors into reporting.
- CGT due: 18% on the part of the gain that fits inside your unused basic rate band (GBP 50,270 of income less your salary) and 24% on the rest, with property and other assets now taxed at the same rates. A GBP 20,000 gain on a GBP 30,000 salary costs GBP 3,060; the same gain on GBP 60,000 costs GBP 4,080.
- Gain kept after tax: the whole gain minus the tax. Gains inside ISAs and pensions, on your main home, on cars and on gifts between spouses are exempt and never enter the sum.
- Allowable costs (advanced): buying and selling costs such as broker fees, stamp duty, legal fees and capital improvements (not repairs) are deducted from the gain before anything else.
- Capital losses (advanced): losses realised in the same year offset gains automatically, and unused losses carry forward indefinitely if reported to HMRC within four years, so a bad investment at least reduces the tax on a good one.
- Type of asset (advanced): shares and residential property share the same 18% and 24% rates in 2026/27, but property has a 60-day reporting deadline. Business sales qualifying for Business Asset Disposal Relief are taxed at a flat 18% (up from 14%) on a GBP 1 million lifetime limit.
- 50/50 split with a spouse (advanced): transfers between spouses and civil partners are tax free, so putting an asset into joint names before sale doubles the exempt amounts and uses the lower earner's basic rate band. The card shows the combined tax and the saving against selling alone.
- Effective rate (advanced): tax as a share of the whole gain, usually well below the headline rate once the exempt amount is counted.
- Report and pay by (advanced): UK residential property gains must be reported and paid within 60 days of completion; everything else goes on the self assessment return due 31 January after the tax year ends, or through HMRC's real time service.
- Caveats: a simplified estimate using England, Wales and Northern Ireland income bands. Not financial advice.
Source and further reading: GOV.UK (HMRC): Capital Gains Tax.