UK Capital Gains Tax calculator that works from your actual trades
Other calculators ask for a gain you've already worked out. This one computes it: upload your broker CSV and get HMRC share matching — same-day, 30-day bed & breakfast, Section 104 pool — per disposal, per tax year. Free, on this page, no account needed.
Your file is parsed in your browser and never uploaded · No ads · Estimates, not tax advice
Drop your broker CSV here
Trading 212 · Freetrade · Hargreaves Lansdown · or any CSV with date / type / quantity / price columns
What this calculator models
- HMRC share identification in the statutory order: same-day → 30-day bed & breakfast → Section 104 pool
- The £3,000 annual exempt amount (and the correct historical AEA for earlier years)
- The 30 Oct 2024 mid-year rate change, split by disposal date
- Fees: buy fees are allowable costs; sell fees reduce proceeds
- Foreign-currency trades converted at the transaction-date exchange rate
- Loss netting against gains before the exempt amount, per HMRC ordering
What it deliberately doesn't
- Corporate actions (splits, mergers, rights issues) — the in-app import flags these for review instead of guessing
- Carried-forward losses from years before your CSV starts — add earlier history for full accuracy
- Residential property, EIS/SEIS/VCT reliefs, and employee share schemes
- The £100k personal-allowance taper in the band split above
Estimates, not advice. For your return, figures must be checked against your records — the full report in the app shows every input so your accountant can verify it.
Common questions
›What is the Section 104 pool?
All shares of the same class in the same company that aren't matched by the same-day or 30-day rules form a single pool with one average cost. When you sell, your allowable cost is the pool average — not first-in-first-out, and not the price of the specific shares you think you sold. This calculator maintains the pool for you from your trade history.
›What is the 30-day bed and breakfast rule?
If you buy the same share within 30 days after selling it, the sale is matched against the repurchase — not the pool. It exists to stop "bed and breakfasting" (selling to realise a gain within the allowance and rebuying the next day). It's the rule DIY spreadsheets miss most often, and it can change your gain substantially.
›Do I need to report at all? The allowance is only £3,000.
You must report if your total gains exceed the £3,000 annual exempt amount, or (when filing a return anyway) if your total proceeds exceed £50,000. The allowance was £12,300 as recently as 2022/23 — hundreds of thousands of investors owe CGT for the first time and don't know it yet.
›Which brokers does the CSV upload support?
Trading 212, Freetrade and Hargreaves Lansdown export formats are recognised directly, and a generic reader handles most other CSVs with date/type/quantity/price columns. Anything else — including PDF statements and contract notes — the AI import inside the app can read after you create a free account.
›When is the tax due?
Share disposals go on your Self Assessment return: report by 31 January following the end of the tax year (so 2025/26 disposals are due by 31 January 2027). There's no 60-day deadline for shares — that only applies to UK residential property.