Tax-Loss Harvesting for Crypto in the UK: A Complete Guide

Tax-loss harvesting is the strategy of deliberately selling assets at a loss to offset gains you have made elsewhere. In crypto, where volatility is extreme and many portfolios contain underwater positions, it is one of the most effective legal ways to reduce your tax bill. Here is how it works under UK rules.

The basic concept

Suppose you sold some Bitcoin earlier this year for a £10,000 gain. You also hold Ethereum that is currently £4,000 below what you paid for it. If you sell that ETH now, you realise a £4,000 loss. Your net taxable gain drops to £6,000. At the 24% higher-rate CGT, that saves you £960 in tax.

How losses work under HMRC rules

Capital losses can be used to offset capital gains in the same tax year. If your total losses exceed your total gains, you can carry the remaining losses forward indefinitely and use them against gains in future years. You must report losses to HMRC within four years of the end of the tax year in which they occurred, or you lose the right to use them.

The 30-day rule trap

Here is where many crypto investors make a costly mistake. HMRC's 30-day "bed and breakfasting" rule states that if you sell a token and repurchase the same token within 30 days, the sale is matched against the repurchase — not the general pool. This effectively cancels out your loss. If you sell ETH at a loss and buy ETH back the next day, HMRC treats it as if nothing happened.

Legitimate strategies

To work around the 30-day rule you have a few options. Wait 31 days before rebuying — this is the safest approach, but you risk the price moving against you. Buy a correlated but different asset — for example, selling ETH and immediately buying a different large-cap token to maintain market exposure, then switching back after 31 days. Use a different wrapper — this is common in traditional finance (selling shares and buying an ETF that tracks the same index) and can apply to crypto in some cases, though HMRC may challenge aggressive interpretations.

When to harvest losses

The best time to harvest losses is toward the end of the tax year (5 April in the UK), when you have a clear picture of your total gains. However, opportunities can arise at any time during market downturns. Review your portfolio monthly to identify positions trading below cost basis.

What to watch out for

Do not harvest losses on tokens you believe will recover strongly in the short term — the 30-day waiting period means you could miss a rebound. Be aware that transferring tokens between your own wallets is not a disposal and does not trigger a loss. Make sure your record-keeping is precise — HMRC can request transaction logs going back years.

Carrying losses forward

If you have a net loss for the year, you are not required to use it all immediately. You can carry unused losses forward and apply them against future gains. This is particularly valuable in years when you have large gains from selling long-term holdings.

Manually scanning your portfolio for harvesting opportunities is time-consuming. CryptoLens automatically identifies positions trading below your cost basis and estimates the tax saving if you realise each loss — giving you a clear action plan before the tax year ends.