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.
The same trades, in eight other countries
Pooling is a British answer, not a general one. Each of these is a genuinely different method rather than the American one reskinned, and each has its own free tool here.
No pooling rules in front: subsection 47(1) averages every identical property into one adjusted cost base across every account you own, and the superficial loss rule looks thirty days in both directions rather than only forward. Work out Canadian ACB →
FIFO parcels, each with its own twelve-month clock, and half the gain discounted — but only after capital losses are applied, and the year ends on 30 June rather than 5 April. Work out the Australian discount →
The one that breaks every engine built somewhere else: the gain is a fraction of what your whole portfolio cost, sized by its value at the moment of the disposal, so the asset you sold appears nowhere in the arithmetic — and swaps between digital assets are not taxable at all. Work out the French formula →
One average cost per asset across everything held, no schablonmetod — and thirty per cent of every loss simply not deductible, so a year you broke even on is still taxable. Work out the Swedish K4 →
The only place here where the usual bug runs the other way: a deemed acquisition cost of 20 per cent of the sale price — 40 after ten years — taken whenever it beats the real one, so an engine that just does proceeds minus cost overstates the tax. Work out the Finnish deduction →
Changes the question rather than the method: no capital gains tax at all, a deemed return on the value held at 00:00 on 1 January, and a counter-evidence rule whose «actual return» counts unrealised change, allows no costs and cannot go below zero. Work out the Dutch box 3 →
The widest spread of all: a gain is personal income in box 20 at up to 53 %, a loss is a deduction in box 58 worth about 26 %, and as a rule they do not offset each other at all. Work out the Danish boxes →
Held more than a year and a private sale is not taxable at all — §23 EStG — rather than taxed at a lower rate. There is no annual exempt amount in the British sense; there is a threshold that taxes the whole gain once it is reached.
Harvesting into a UK pool
Sell at a loss and buy the same token back within 30 days and s.106A(5) matches the repurchase to the disposal, so the loss you meant to bank is computed against the new acquisition instead of the pool. The trade still happened; the loss largely did not. Work out what you are holding at a loss →
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.