UK Crypto Tax Calculator —
HMRC-Compliant for 2025/26 and 2026/27

For the 2025/26 and 2026/27 tax years, crypto Capital Gains are taxed at a flat 18% (basic rate) or 24% (higher/additional rate), with no split-year adjustment. The annual exempt amount is £3,000, frozen across both years. 2024/25 was a split year — disposals before 30 October 2024 were taxed at 10%/20% and those from 30 October 2024 onwards at 18%/24% — and ChainTax computes the SA108 Box 51 split-year adjustment for it automatically, so you never need to apportion gains by hand.

HMRC requires you to pool acquisitions of the same asset and use the average cost as the cost basis for any disposal. ChainTax builds a Section 104 pool per asset, applies same-day matching first, then 30-day Bed & Breakfast, then S104 average cost — in HMRC's exact priority order. Every disposal shows the matching rule used, the pool snapshot before and after the sale, and the price source.

On-chain: Ethereum, Arbitrum, Optimism, Base, and Polygon — public wallet addresses only, never private keys or signing permissions. CSV import: Coinbase, Binance, Kraken (auto-detected), plus Koinly export for any exchange Koinly already supports. Solana, Avalanche and BSC are not yet covered on-chain — for those, manual entry or a Koinly CSV is the workaround.

Yes — free for up to 200 transactions per tax year, including the full report preview. You only pay when you download the SA108-ready PDF or CSV. Light is £49 for up to 2,500 transactions, Active is £99 for up to 10,000. One-time payment per tax year, no subscription.

Every disposal is matched against HMRC rules in the correct priority order (same-day → 30-day B&B → Section 104). 32 protocol-specific classifiers handle Uniswap, Aave, Lido, Curve, GMX, Seaport, Treasure and others — protocols that most crypto tax tools misclassify as phantom gains. Every transaction shows a confidence rating (High, Medium, Low). Anything we cannot recognise lands in a Needs-review queue rather than getting a wrong answer silently.

You can preview your full report — every disposal, every matching rule, every box on SA108 — before paying. Once you pay and download, refunds are available within 14 days under UK consumer law for unused purchases. Email hello@chaintax.co.uk to request a refund. Stripe processes the refund directly to your original payment method.

For the 2025/26 tax year (6 April 2025 to 5 April 2026), online Self Assessment is due by 31 January 2027 and paper returns by 31 October 2026. The 2024/25 deadlines — online 31 January 2026, paper 31 October 2025 — have passed, though you can still file a late or amended return. SA108 is the supplementary capital gains page: for 2024/25 onwards, boxes 13.1–13.8 and Box 51 cover crypto disposals specifically.

Yes. Generate a shareable read-only link from the report — your accountant sees every disposal, every matching rule, the cost basis before and after each sale, and the price source with a confidence rating. No login needed on their side. The PDF report pre-fills SA108 boxes 13.1–13.8 plus Box 51 for direct transcription onto the return.