Features / Crypto Tax Calculator
HMRC's rules, applied automatically.
Your gain in minutes.
HMRC has specific rules for calculating crypto capital gains. The order you match sales to purchases matters. Get it wrong and you either overpay or underpay — neither is good.
Polyconomic applies the correct rules automatically: same-day matching first, then the 30-day bed-and-breakfast rule, then the section 104 share pool. Every time, in the right order.
HMRC matching rules
The three rules HMRC requires, in the right order
HMRC's rules are designed to prevent certain tax-avoidance strategies. We apply them automatically in the legally correct sequence.
Same-day rule
If you buy and sell the same cryptocurrency on the same day, HMRC requires those transactions to be matched against each other first — before any other matching takes place.
30-day rule
If you sell a cryptocurrency and then buy it back within the following 30 days, HMRC requires the sale to be matched against the repurchase. This prevents "bed and breakfasting" — selling to realise a gain or loss and immediately buying back.
Section 104 pool
Any remaining sales are matched against your average cost pool — a running total of all your purchases of that asset, divided by the number of coins held. This is the main pool used for most trades.
What we calculate
Everything HMRC wants to know
Capital gains on disposals
Every sale, swap, spend, or gift of cryptocurrency is a disposal for HMRC purposes. We identify and calculate the gain or loss on each one.
Crypto income
Staking rewards, mining income, airdrops that constitute income, and interest-bearing accounts are treated as income, not capital gains. We report them separately.
Annual CGT allowance
We show clearly whether your total gains for the year are above or below the £3,000 annual exempt amount, and exactly what is left as taxable.
Loss relief
Losses reduce your taxable gains. We calculate your total losses for the year and show the net position — which may be significantly lower than your gross gains.
Allowable costs
Transaction fees, gas fees, and other acquisition costs are deducted from your gains where HMRC allows. We include them automatically.
Tax year summaries
A clean summary for every tax year in your history — total disposals, total proceeds, total gains, total losses, and the net taxable gain.
The report
A PDF you can actually file from
The figures you need to complete your HMRC Self Assessment return, in a layout that makes sense.
SA108-compatible layout
The PDF follows the structure of HMRC's Capital Gains Summary supplementary page. Every figure is where you expect it.
Trade-by-trade breakdown
Every disposal listed with its date, proceeds, allowable costs, and gain or loss. Full traceability from summary to individual trade.
Plain English throughout
No tax jargon. Every section has an explanation of what the figure means and where it goes on your return.
Shareable with your accountant
Download and send it directly. Accountants tell us it is the clearest crypto tax report they receive from clients.