How CryptoCGT works out your crypto tax: methodology & accuracy

UK crypto Capital Gains Tax has a precise set of rules, and getting them slightly wrong gives a slightly wrong number, on a return you sign. CryptoCGT exists to get the number rightand to let you check it. Here's how.

1. It implements HMRC's rules, to the letter

Every disposal is matched to a cost using HMRC's ordering: same-day first, then the 30-day “bed & breakfast” rule, then the Section 104 pool. The pool keeps a running average cost per coin, exactly as the HMRC Cryptoassets Manual sets out. The correct rates and annual exempt amount for each tax year are applied automatically, including the 30 October 2024 rate change (the rise to 18% and 24%).

2. It's checked against HMRC's own examples, to the penny

This is the part nobody else shows you. HMRC publishes its own worked examples (CRYPTO22251 to CRYPTO22256), real numbers with the published answer. CryptoCGT reproduces every one of them to the penny, and we run all six as automated tests on every change, so it can't silently drift. Follow the link and check any of them against your own report.

Checked two independent ways

On top of HMRC's examples, the engine is cross-checked against BittyTax, a separate open-source UK CGT calculator. When two independent implementations of the same law agree to the penny on the same trades, you can trust the figure, and that's a much stronger guarantee than “trusted by thousands of users.”

3. Every figure shows its working

Click any number and you see exactly which trades and which rule produced it: proceeds, each matched cost, and the gain, line by line. Nothing is hidden, so you (or your accountant) can check it before you file, and so you understand why the number is what it is.

4. It never hands you a confidently-wrong number

A tax figure is only useful if it's right. If your data is incomplete (a missing cost basis, an unpriceable coin, a sale we can't reconcile), CryptoCGT says so and marks the figure provisional, and won't let you download a report it can't stand behind. The most common complaint about crypto-tax tools is numbers that are wrong or change every time; this reliability gate is how we avoid that.

5. Your data, and your funds

CryptoCGT works from a CSV export or manual entry only. We never ask for exchange API keys, never connect to your accounts, and have no way to move or withdraw your crypto. Read-only by design. See how to export a CSV from your exchange.

6. What we deliberately don't do

Being honest about scope is part of being trustworthy:

We compute Capital Gains Tax. Income events (staking, most airdrops, mining) are flagged for you to declare, but we don't compute Income Tax.
Where a tax treatment is genuinely uncertain or still a proposal rather than settled law, we flag it rather than quietly guessing.
We are an information tool, not a regulated tax adviser, and we can't file on your behalf. You remain responsible for your return, so for your specific circumstances have a qualified accountant review the figures before you file.

7. Transparent pricing

It's free to compute and see your full number, with no account needed. You only pay £49 per tax year (£29 for founding members) when you download the finished SA108 report, a flat one-off, not a subscription, and never a charge for an empty report.

Sources

HMRC Cryptoassets Manual (including the worked examples CRYPTO22251 to CRYPTO22256)
BittyTax: independent open-source UK CGT calculator

See your own number — free, no account

Drop your exchange CSV and read your full Capital Gains Tax figure on screen, with the Section 104 working shown. You only pay if you download the report.

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This guide is information, not tax advice.Figures and thresholds are for the tax year shown (England, Wales & Northern Ireland; Scottish income tax bands differ). Rates and rules can change, and your own position may differ — check your circumstances and speak to an accountant before you file. CryptoCGT is an information tool, not a regulated tax adviser.