Best crypto tax calculator UK, tested with the working shown
On this page
We make one of the calculators below, so treat this page as a vendor’s comparison with its cards face up, every claim dated, every test repeatable by you in a browser tab. The honest answer to “best” starts with a question no calculator page asks out loud: how many times did you buy the token you sold? Because that single fact divides the field into calculators that can be right about UK tax and calculators that cannot.
The field, as tested on 31 August 2026
Recap’s calculator, at recap.io/cryptotaxcalculator, is the best of the simple ones and the one to beat. Tested today: it runs on the page, free, no signup, takes one buy, amount, date, price, one sell, applies the £3,000 exemption, and its notes reference the section 104 pool. Its own disclaimer says what we would say, it “provides estimates for a single transaction and does not account for all possible tax scenarios”. For a person who bought once and sold once, it gives a sound estimate.
Koinly’s calculator page at koinly.io/crypto-tax-calculator/gb/ refused our automated check today, a 403, as their site has before, so we cannot tell you first-hand what runs on that page, and will not describe unverified behaviour. What their page cannot change is the shape of the product behind it: estimates on the page, full computation in their cloud, per-tax-year pricing, the model we have compared line by line.
The generalist calculators. When we walked the UK calculator search results on 26 August, the pages winning most of them were free general CGT calculators from Taxfix and The Accountancy Partnership, working on the page, no crypto specifics, one buy and one sell. Fine for a sanity check of the rates arithmetic, silent on everything that makes crypto hard.
The gains.tax calculator, ours. Free, signed out, no email gate, and different in the one way we built this whole product around: it takes multiple acquisitions of the same token, pools them under section 104, applies the same-day and 30-day rules, and names the rule that matched each disposal. When the estimate outgrows the page, the full app runs the identical engine over your entire imported history, in your browser, free under 1,000 transactions.
The test that separates them
| The calculator can | Simple tools | gains.tax |
|---|---|---|
| One buy, one sell, current rates and allowance | Yes | Yes |
| Run free on the page, no email | The good ones | Yes |
| Pool several buys of one token, section 104 | No | Yes |
| Apply same-day and 30-day matching | No | Yes |
| Name the rule behind each figure | No | Yes |
Why the bottom three rows decide it: suppose you bought ETH three times, at £1,000, £2,000 and £3,600, then sold some. UK law does not ask which coins you sold, there is no picking the £3,600 lot to shrink the gain. Your cost is the pooled average of every purchase, adjusted first by same-day and 30-day matching, and a rebuy within 30 days of a loss-making sale rewrites the answer again without telling you. Feed that history to a one-buy calculator and it computes something, confidently, in pounds, and the something is another jurisdiction’s tax. This is not the tools being lazy, it is the page format being too small for UK law, which takes current rates of 18% and 24% above a £3,000 allowance, both verified today, and applies them to a gain the pooling rules define.
Choosing in three sentences
One buy, one sell, wanting a fast estimate: Recap’s page calculator is good, and the generic firm calculators check the same arithmetic. Anything more, multiple buys, a swap-heavy year, losses and rebuys: use a calculator that pools, because the simple format cannot be patched into correctness. And when the real question is your whole year rather than one disposal, the calculator worth trusting is the one that shows its working, disposal by disposal, rule by rule, before you put a number on a legal document.
An estimate from any of these pages, ours included, is an estimate, not advice, and not a filing. The filing needs the full computation, the software comparison covers who charges what to produce it, and the version that costs nothing under 1,000 transactions and never sees your data is one tab away.