For HMRC nudge letter recipients
You have 60 days to respond. For most UK investors that means recomputing gains under Section 104 pooling, separating income from disposals, and either confirming the return or amending it. ChainTax does the calculation end-to-end.
Free up to 200 transactions. Pay only when you download the report.
60 days
to respond
The letter is informal — but ignoring it triggers a formal enquiry. Replying inside the window keeps it routine.
~65,000
letters in 2024/25
More than double the prior year. CARF data feeds from UK exchanges went live January 2026 — volume will keep climbing.
Lower penalties
if you act first
Unprompted disclosure typically halves the penalty band vs HMRC finding it through enquiry. The earlier you correct, the cheaper it gets.
Which path is mine?
Pick by transaction count and activity type. Most retail investors land in the first column.
Most common
Under 10,000 transactions
Coinbase, Binance, Kraken plus some DeFi. Run it yourself.
Above the cap
Over 10,000 transactions
Heavy DeFi, multi-wallet, NFT activity. We run the sync for you.
Specialist needed
Trade or business activity
Mining as a trade, company crypto, gambling-like activity.
Before you buy a self-serve plan
If you mined crypto as a business, ran a node commercially, the activity sits inside a UK company, or you suspect the undeclared amount is large enough to fall under HMRC's deliberate category, the right first step is an accountant — not a self-serve tool. Email hello@chaintax.co.uk and we'll point you at the right help.
If self-serve fits
HMRC matching rules done right
Same-day → 30-day bed-and-breakfast → Section 104 average-cost pooling, in the order HMRC requires. 2024/25 split-year CGT rate (10/20% before 30 Oct, 18/24% after) applied per disposal.
SA108 boxes 13.1–13.8 + Box 51
The dedicated crypto section introduced for 2024/25, mapped automatically. PDF report formatted for direct transcription onto the return.
Show Working — full audit trail
Every disposal shows the matching rule, the S104 pool snapshot before and after, and the price source with confidence rating. If HMRC asks for working, you have it.
Multi-year filing
The letter often references several years. Each tax year is a separate report; loss carry-forward is automatic across years. Bundle 2 years for a £19–£29 saving.
How it works
Sign up and add your wallets
Public addresses only — never private keys or exchange API keys. Add Coinbase, Binance, or Kraken via CSV import in the same flow.
The engine classifies every transaction
Disposals, income, transfers, liquidity — across Ethereum, Arbitrum, Optimism, Base, and Polygon. 27 dedicated protocol handlers plus generic-swap fallback.
Review the report — for free
Up to 200 transactions classify free. You see the full summary, the disposal breakdown, and Show Working before paying. No surprises.
Pay per tax year, download PDF + CSV
£49 Light / £99 Active. One year per purchase, no subscription. The PDF maps directly onto the SA108 boxes HMRC referenced in the letter.
No tax tool is perfect. Here's what ChainTax cannot yet handle automatically — and what you should check manually or discuss with your accountant.
Full detail: How it works → Known limitations
FAQ
I just got an HMRC nudge letter about crypto — what do I actually do?
You have 60 days from the date on the letter. The letter asks you to confirm whether your past self-assessment returns correctly reported your crypto disposals — every swap, sale, and DeFi event, not just GBP cash-outs. Gather your full transaction history, recompute the gains under HMRC rules (Section 104 pooling + same-day + 30-day B&B), and either confirm your returns are correct or amend them. Voluntary correction before HMRC opens a formal enquiry significantly reduces penalties.
Can I sort this out with ChainTax, or do I need an accountant?
For most UK retail investors — exchange use plus some DeFi, under 10,000 transactions across all wallets — ChainTax handles the calculation end-to-end. Connect your wallets and exchange CSVs, the engine classifies every event, and you get an SA108-ready PDF and CSV with full Show Working. If your situation involves mining as a trade, business or company crypto activity, large undisclosed amounts, or over 10,000 transactions, an accountant or our Concierge service is the better starting point.
How much does it cost?
Free up to 200 transactions. £49 for Light (up to 2,500 transactions per tax year) or £99 for Active (up to 10,000). One-time payment per tax year — if HMRC is asking about multiple years, you pay per year, with a 2-year bundle option. Concierge sync (we run it for you, over 10k transactions) is quote-first, typically £249–£449.
How far back can HMRC investigate?
Four years for innocent error, six years for careless error, and up to twenty years for deliberate non-disclosure. Most UK investors' entire crypto history falls inside the lookback window. The lookback is one reason voluntary disclosure matters — coming forward unprompted lowers the penalty band even on older years.
I don't think I owe much. Do I still need to respond?
Yes. Even if your gains are below the annual exempt amount (£3,000 for 2024/25 onwards), HMRC still expects a response confirming that. Ignoring a nudge letter doesn't close the file — it escalates it from informal to formal. The cheapest path is to run the numbers, confirm where you stand, and reply within the 60 days.
What if I used DeFi protocols HMRC has never named?
HMRC's Cryptoassets Manual (CRYPTO10000–CRYPTO45700) covers principles, not protocol-specific guidance for every contract. The engine applies the principles consistently — Uniswap V2/V3, Curve, Aave, Lido, Balancer, GMX, Seaport, Treasure, and 19 others have dedicated handlers. For protocols outside the dedicated set, generic-swap and liquidity heuristics catch the common shapes; anything novel surfaces as Needs Review for manual classification.
Background reading: the full guide to HMRC's nudge-letter campaign.
Free up to 200 transactions. Pay only when you're ready to download the report. No subscription, no auto-renewal.
ChainTax is a tax calculation tool and does not provide tax, financial, or legal advice. Verify your figures with a qualified adviser before filing.