HMRC does not use FIFO. Here is what it actually does.
Section 104 TCGA 1992 pools every unit of a token at one averaged cost. Sections 105 and 106A make a disposal match same-day and next-30-days acquisitions first. Get the order wrong and the gain is wrong — and the difference does not wash out in a later year. Paste your trades below and see which rule matched what.
One per line:
date, buy|sell, asset, quantity, total £, fees £ — fees optional.
Dates as YYYY-MM-DD. Everything in pounds, because HMRC wants sterling at the
date of each transaction.
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Shown because this is what an engine built for the United States produces when it is pointed at a UK return. It is not an alternative treatment; it is the wrong one.
Every leg names the section it comes from. If a figure here ever disagrees with your own reading of the statute, the section is right there to check it against.
Cryptoassets belong in “Other property, assets and gains” — not the listed-shares section. Losses of the year come off gains of the year before the annual exempt amount applies, because using the exemption first would waste it.
The three rules, in the order they apply
s.105(1)(b). Anything you bought on the day you sold is matched to that sale first, at its own cost, before the pool is touched. Day traders hit this constantly and it is why their pooled cost barely moves.
s.106A(5), bed and breakfasting. Acquisitions in the 30 days after the disposal are matched next. Forward-only: a purchase before the sale is an ordinary pool acquisition. This is the rule that makes a purchase you have not made yet change the cost of a sale you already made, and it is the one almost everybody misses.
s.104. Everything else comes out of one pool holding every remaining unit of that token at a single averaged cost. A disposal takes a proportion of the pool and the pool keeps the remainder exactly — rounding the split would leak pennies into every later disposal of the same asset.
Questions
Does HMRC use FIFO for crypto?
No, and this is the single most consequential thing to get right. Section 104 of the Taxation of Chargeable Gains Act 1992 puts every unit of the same token into one pool with one averaged cost, and a disposal takes a proportion of that pool. FIFO, LIFO and specific identification all produce numbers HMRC does not recognise. A tool that applies its American logic with a currency symbol swapped is not slightly off — it is answering a different question.
What is the 30-day rule and why does it change a sale I already made?
Section 106A(5) matches a disposal against acquisitions made in the 30 days AFTER it, before the pool is touched. It exists to stop 'bed and breakfasting' — selling to crystallise a loss and buying straight back in. The consequence surprises people: a purchase you make three weeks after a sale retroactively becomes the cost of that sale. Sell 1 BTC for £18,000 that you had pooled at £30,000 and you look like you have a £12,000 loss; buy 1 BTC back twenty days later for £18,500 and the real answer is a £500 loss.
In what order do the rules apply?
Same day first (s.105(1)(b)), then the following 30 days (s.106A(5)), then the s.104 pool. The order is not a preference — it is statutory, and the same trades matched in a different order give a different gain that does not wash out later.
Does the 30-day window look backwards too?
No. It is forward-only: acquisitions in the 30 days after the disposal. An acquisition three weeks BEFORE a sale is an ordinary pool acquisition. Matching backwards would apply a rule that does not exist.
Which SA108 section do cryptoassets go in?
'Other property, assets and gains'. HMRC treats cryptoassets as chargeable assets rather than as listed shares, so they do not belong in the shares section — a common and visible filing error.
Do I need to file if my gains are under the annual exempt amount?
Possibly, and for two separate reasons. HMRC asks for the pages where your total proceeds exceed the reporting threshold even if the gain is covered, and a loss you never reported is a loss you cannot carry forward. The exempt amount also fell twice in quick succession — £12,300, then £6,000, then £3,000 — so the year matters far more than it used to.
How are losses and the exemption ordered?
Losses of the year come off gains of the year first, and only then does the annual exempt amount apply. Brought-forward losses are used only down to the exempt amount, never through it — a loss used below the exemption is wasted, and wasting one costs real money.
What does this tool not decide?
Whether you are trading rather than investing, which moves everything to income tax; residence, domicile and the remittance basis; whether a particular DeFi arrangement was a disposal, which HMRC's own guidance makes fact-dependent on beneficial ownership. Those are questions about a person, not about a ledger, so we surface them and never assume them.
Is anything uploaded?
No. This page computes entirely in your browser — nothing you paste leaves the tab. The full engine, which is the authority for paid work, applies the same rules with evidence attached to every figure.
Run it on your real history
The full engine applies these same sections with evidence attached to every figure, across every exchange export and wallet address you give it. Free to see the answer. See also the UK country guide.