If a token you hold has gone to zero, you have not made a disposal and you do not have a loss. HMRC is explicit about the related case of a lost key: "misplacing the key does not count as a disposal for Capital Gains Tax purposes." The tokens still exist and you still own them. What turns a worthless holding into a usable loss is a negligible value claim, and the most useful sentence HMRC has written about it is this, from CRYPTO22500:
"As tokens are pooled, the negligible value claim needs to be made in respect of the whole section 104 pool, not the individual tokens."
That sentence appears nowhere in the customer-facing guidance, and it removes a choice people assume they have. Your holding of one token is a single pooled asset with one averaged cost: you cannot claim on the expensive tranche and keep the cheap one, or write off half a holding while keeping the rest alive in hope of recovery. Pools are per token, though, so a dead altcoin does not touch your bitcoin pool.
Four things, not one
Keeping these apart is most of the work. A disposal is an occasion of charge. A negligible value claim deems a disposal and immediate reacquisition of something you still own. The loss then arises. Notifying it is a fourth step, without which it is not allowable — HMRC calls that "a separate claim from the negligible value claim".
Two conditions govern it. You must still own the asset, and it must have become of negligible value while you owned it — HMRC reads "negligible" as "worth next to nothing". No published list covers any cryptoasset, so every claim is built from scratch on your own evidence.
What it is worth
Take a pool of 100,000 units bought in two lots, 40,000 for £18,000 and 60,000 for £4,500 — a pooled cost of £22,500. The token is worthless, you have £26,000 of other crypto gains the same year and £28,000 of taxable income after your personal allowance.
Without a claim, £26,000 less the £3,000 allowance leaves £23,000. Added to income that crosses the £37,700 basic rate band, so £9,700 is taxed at 18 per cent and £13,300 at 24: £4,938. With the claim, the £22,500 loss comes off the gains first, leaving £3,500; the allowance takes that to £500 at 18 per cent. Tax falls to £90, a saving of £4,848, or 21.55p in each pound of loss.
Note the order. A current-year loss comes off the gains in full, before the allowance, and can push them below £3,000 — in which case the allowance is wasted. Only loss beyond the year's gains carries forward, where it cannot take gains below the allowance.
The two clocks
There is no deadline on making the claim, but there are hard limits on what it is worth. A claim can be backdated only to a date not more than two years before the start of the tax year in which it is made: anywhere in 2026/27 that floor is 6 April 2024, and from 6 April 2027 it becomes 6 April 2025. Anyone whose tokens died in the 2022 collapse has already lost the ability to date a claim back to that year. Separately, the loss must be notified within four years of the end of the tax year it accrued in — a 2022/23 loss by 5 April 2027, a 2025/26 one by 5 April 2030. You can claim forever; you simply cannot get the loss.
| Other gains; income | £26,000; £28,000 |
| Tax without, and with, the claim | £4,938; £90 |
| Saved | £4,848, or 21.55% of the loss |
| Backdating floor, claim in 2026/27 | 6 April 2024 |
| SA108 boxes | 13.5, code NVC in 13.6, detail in 54 |
Where HMRC contradicts itself
On theft, the Cryptoassets Manual says flatly that "victims of theft cannot claim a loss for Capital Gains Tax". The Capital Gains Manual page it points you to says the opposite: where "there is no likelihood that the asset will be recovered, a negligible value claim under section 24(2) TCGA 1992 would be competent". The statute supports the second. Theft is not a disposal, which is all the crypto page is saying, but a claim is available once recovery is hopeless, unless insured. CRYPTO22400, 22450 and 22500 have not been revised since March 2021; the Capital Gains negligible value pages were restructured last October.
A second contradiction is quieter: three HMRC pages say an asset cannot have been worthless when acquired, while the statute adds a condition they omit, under which a token received from a spouse can still be claimed on.
An exchange collapse HMRC has not addressed at all. Two things are safe to say: inaccessibility is not a disposal, and a claim will struggle while an administrator is signalling a distribution, because a right worth something is not worth next to nothing.
Sources, retrieved 19 October 2026: Cryptoassets Manual CRYPTO22200, 22400, 22450 and 22500 (updated 28 November 2025); Capital Gains Manual CG13125, CG13130, CG13155, CG15800 and CG21500 (updated 19 October 2026; the negligible value pages restructured 16 October 2025); TCGA 1992 sections 16 and 24 and TMA 1970 section 43; gov.uk/capital-gains-tax/losses and /guidance/negligible-value-agreements; the SA108 form and notes for 2025/26, HS286 (2026) and the rates and allowances page. Allowance £3,000, rates 18 and 24 per cent and band £37,700 are unchanged across 2025/26 and 2026/27. Contested: CRYPTO22450 and CG13155 disagree on whether a theft victim can claim, and HS286 omits the cryptoasset boxes the SA108 notes require. Unverified: HMRC has published nothing on failed-exchange balances. General information, not tax advice, and not a recommendation to buy, sell or hold anything.