Crypto Tax Losses in the UK: Allowable Expenses, Loss Harvesting and Fraud Claims

London — Most UK crypto coverage focuses on the gains. It's more interesting to write about. But for anyone who's been in the market for more than a year, the tax treatment of losses is at least as important — and in a market as volatile as this one, the opportunities to crystallise losses and use them strategically are real.

HMRC's rules on crypto allowable expenses and capital losses are fairly precise. Get them right and you're reducing your tax bill legally and efficiently. Miss them and you're leaving money on the table. There's also one significant trap — crypto fraud — where HMRC's position is considerably less generous than most people expect.

What you can deduct from your gains

Under Section 38 of the Taxation of Chargeable Gains Act 1992, the allowable costs you can deduct from your crypto disposal proceeds are: the original purchase price in sterling, transaction fees paid to get onto the ledger (gas fees on Ethereum, network fees on Bitcoin), advertising costs if you used them to find a buyer, professional fees for drawing up contracts, and the cost of any valuation required to establish the disposal price.

Exchange fees deserve a slightly longer explanation. If you pay a fee in sterling when buying crypto, that fee is added to your cost base — it's part of what you paid. If you pay a fee when selling, it's deducted from your proceeds. For token-to-token swaps, where you pay a fee in a third token or split between the two assets, HMRC splits the fee 50/50 between the acquisition of the new token and the disposal of the old one.

What's not allowable: deposit and withdrawal fees (moving sterling into an exchange account isn't a CGT event, so those fees don't attach to a CGT calculation). Mining equipment and electricity costs don't go here either — they may be deductible against income tax on your mining income, but they're not CGT costs.

Crystallising losses — and the 30-day rule trap

If you hold a position that's fallen significantly, you can sell it before 5 April to crystallise an allowable capital loss in the current tax year. That loss can be set against gains in the same year, or carried forward indefinitely against future gains. You have up to four years from the end of the tax year of disposal to formally claim an allowable loss with HMRC.

The obvious follow-up is to sell and immediately rebuy the same position — locking in the loss while maintaining exposure. This is called bed-and-breakfasting, and HMRC's 30-day rule explicitly blocks it for crypto. If you sell and then rebuy the same token within 30 days, the disposal is matched against the reacquisition's cost rather than the original pool cost. The planned loss simply disappears.

To make a loss count, you need to wait 31 days before buying back in. That works in a relatively stable market. It's a gamble in a fast-moving one — 31 days is enough time for a significant recovery. Some investors take that risk. Others sell into a stablecoin or a correlated asset and reacquire after the waiting period.

Carrying losses forward

Capital losses don't expire. If you had a terrible year in 2022 and made significant crypto losses, those losses are yours to use against future gains — forever, in principle. You do need to have claimed them on a self-assessment return for the year in which they arose. If you didn't report them at the time, you can still claim them retrospectively up to four years after the tax year of the loss.

One nuance: you must use losses to reduce your gains in the year they're made before carrying the remainder forward. And you can only carry losses forward until your net gains in that year reach the annual exempt amount — you don't have to use any more of the carried-forward losses once your gain has been reduced to £3,000.

The fraud trap — where HMRC doesn't help

Here's the part that surprises most people. If you're a victim of crypto theft — someone hacks your wallet, drains your exchange account — HMRC does not treat that as a disposal. Because you technically still own a right to recover the stolen assets, you haven't made a CGT disposal and therefore cannot claim a capital loss.

For fraud — where you bought tokens that turned out to be worthless — HMRC's position is a little different. If the tokens had value when you acquired them and subsequently became worthless (not fraudulent from day one), you can file a negligible value claim. That's treated as if you disposed of and immediately reacquired the tokens at their current negligible value, crystallising the loss. But it only works for tokens that genuinely had some value at the point of acquisition. If a project was a rug pull from the start and the tokens were never worth anything, HMRC won't accept a negligible value claim.

The practical upshot: if you've lost money to crypto fraud, document everything carefully, and consider whether you held tokens of any genuine prior value. A negligible value claim through your self-assessment return is the closest thing to tax relief HMRC offers. It's imperfect, but it's what exists.