Same-day rule
Shares bought on the same day as the sale are matched first, at that day’s purchase cost — before anything else.
UK Capital Gains Tax Calculator for Shares
Enter your buys and sells — the calculator applies HMRC’s same-day, 30-day bed-and-breakfast and Section 104 matching rules, deducts the £3,000 allowance and estimates your CGT at 18% or 24%.
Runs 100% in your browser — nothing is uploaded, ever
Your transactions (GIA only — ISA & SIPP disposals are tax-free)
Everything recalculates as you type.
⚠️ Pence trap: London-listed shares are often quoted in pence (GBX). Enter prices in pounds — a quote of 1,234p is £12.34.
Your estimate
Estimated CGT due — 2026/27
£0
Net gains in year
£0
Annual exemption used
£0
Taxable gain
£0
Avex builds this from your broker statements — automatically.Upload your Trading 212, eToro or HL statement; parsing runs locally, and your CGT position stays current all year.
Request early access →The rules, in order
How HMRC matches your sales to your purchases
Every disposal is matched in this exact order. Getting it wrong is the most common DIY CGT mistake.
30-day “bed & breakfast” rule
Shares repurchased within 30 days after the sale are matched next, at the repurchase cost. This blocks sell-and-rebuy allowance harvesting.
Section 104 pool
Whatever remains is matched against your pooled average cost of all other shares of that class you’ve ever bought and still hold.
Quick answer: in 2026/27 you pay capital gains tax on UK share profits above the £3,000 annual exempt amount — at 18% (basic-rate taxpayers) or 24% (higher/additional rate). Gains are calculated per disposal using HMRC’s share-matching rules, and losses in the same year offset gains automatically.
The key numbers for 2026/27
| Item | Value | Source |
|---|---|---|
| Annual exempt amount (AEA) | £3,000 | gov.uk — CGT allowances |
| Rate — basic-rate taxpayer | 18% | gov.uk — CGT rates |
| Rate — higher / additional rate | 24% | gov.uk — CGT rates |
| Reporting threshold (proceeds) | £50,000 if you already file Self Assessment | HMRC SA108 notes |
| ISA / SIPP disposals | Not taxable — exclude them | gov.uk — ISAs |
What this calculator does — and doesn’t
Does: same-day, 30-day and Section 104 matching per HMRC’s rules; buy fees added to cost and sell fees deducted from proceeds; in-year loss offset; the AEA; a carried-forward loss figure; per-disposal audit trail you can check against your broker’s numbers.
Doesn’t: straddle the basic/higher band boundary (if a gain pushes your income across it, part is taxed at each rate); handle corporate actions (splits, mergers, rights issues), accumulation-fund equalisation, or non-GBP conversion — convert to GBP at the transaction-date rate first. For anything beyond plain share disposals, confirm with an accountant.
If your gain is taxable, what next?
Report it on the capital gains pages (SA108) of your Self Assessment return by 31 January following the tax year. Keep your workings — since January 2026 brokers report account data to HMRC under CARF, so HMRC increasingly already knows your proceeds. Your broker’s CSV export is your evidence trail; keep every year’s file.
FAQ
Capital gains on shares, answered
18% for basic-rate taxpayers and 24% for higher and additional-rate taxpayers, applied to gains above the £3,000 annual exempt amount. Gains realised inside an ISA or SIPP are not taxable at all.
This calculator provides estimates for general information only, based on the rates and allowances shown and the data you enter. It is not tax advice, does not cover every situation (band straddling, corporate actions, non-GBP assets, fund equalisation), and no liability is accepted for decisions based on it. Verify your position with HMRC guidance or a qualified adviser before filing. Capital at risk.