Shares CGT Calculator 2026/27
Estimate CGT on shares or funds sold outside an ISA or pension. Enter your figures below - results update instantly.
Section 104 Share Pool Calculator
The hard part of CGT on shares is when you've bought the same holding at different prices over time. HMRC doesn't just use an average - it applies three matching rules in order: the same-day rule, the 30-day "bed & breakfast" rule, then the Section 104 pool (average cost). Enter your buys and sells and this works out the gain on every sale the way HMRC does.
| Date | Type | Quantity | Price/share £ | Fees £ |
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Applies the same-day, 30-day and Section 104 rules for 2026/27 (£3,000 annual exempt amount; 18% basic-rate / 24% higher-rate). One holding at a time. It does not model accumulation-unit notional distributions, corporate actions (splits, mergers) or gifts. Estimates only - not tax advice.
How it works
This calculator uses 2026/27 CGT rates for shares and funds:
- Gross gain = sale proceeds minus original purchase cost minus dealing costs.
- Deduct capital losses, then the annual exempt amount (£3,000).
- The taxable gain is split across the basic-rate and higher-rate bands using your income.
- 18% applies to gains within the basic-rate band; 24% to the remainder.
Share matching rules: HMRC uses a "same-day rule", "30-day rule" and "section 104 pool" to determine the cost base when shares are bought and sold at different times. This calculator assumes a single pool with the cost you enter - it is most accurate for a single purchase and single sale. Use a qualified tax adviser or HMRC's own tools for complex share portfolios.
Worked example
Sale proceeds £25,000 minus purchase cost £10,000 minus dealing costs £50 = gross gain of £14,950. After the £3,000 annual exempt amount, £11,950 is taxable. With income of £40,000, £10,270 of basic-rate band remains, so CGT is £1,849 at 18% and £413 at 24% - a total of approximately £2,262.
Note about ISAs
Shares, funds and investment trusts held inside a Stocks and Shares ISA are entirely free of CGT - dividends and capital gains are both sheltered. The ISA allowance is £20,000 per tax year. This calculator is for assets held outside an ISA or pension.
Official sources
Frequently asked questions
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Are shares inside an ISA subject to CGT?
No. Gains and income inside a Stocks and Shares ISA are completely free of CGT and income tax.
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What are dealing costs?
Broker commissions and stamp duty reserve tax (SDRT) paid on purchase are allowable costs. Platform fees and subscription costs are generally not deductible against CGT.
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What if I bought shares at different times?
HMRC uses share identification rules - same-day, 30-day and a section 104 pool - to calculate the allowable cost. This calculator does not model those rules; enter your best estimate of the average cost for a simple approximation.
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This calculator provides estimates for guidance only and does not constitute tax or financial advice. Tax rules can change and individual circumstances vary. Consult a qualified tax adviser before making decisions based on these figures.