See your unrealised crypto losses before year end

Cost basis is the volume-weighted average price (VWAP) of every inbound transfer of the token over the last 365 days, priced on the receipt date. Bigger tranches weigh more. We ignore inbounds from known spam or drainer contracts.

Current valueis your balance multiplied by today's GBP price.

Unrealised loss = current value − approximate cost basis. We only surface tokens where this is negative.

This is a directional read, not an SA108 figure. The full engine matches every disposal under HMRC same-day, 30-day bed-and-breakfast, and Section 104 rules across every wallet and CEX you connect — that's the figure that lands on your tax return.

A loss is only deductible once you actually sell or swap the position. Holding a token at a loss does nothing for your tax bill — only crystallising it does.

Watch the 30-day rule. If you re-buy the same token within 30 days of crystallising the loss, HMRC's bed-and-breakfasting rules match the loss against that re-acquisition instead of releasing it to your Section 104 pool. The loss still gets used eventually — it's just deferred.

Losses you can't use this year can be carried forward indefinitely, as long as you claim them within 4 years (HMRC CG15800). ChainTax tracks the carry-forward automatically.