HMRC CARF 2026 — what UK crypto investors must know about platform reporting

January 2026 is the UK crypto investor’s 1099-DA moment. From the start of the year, the Cryptoasset Reporting Framework (CARF) requires UK crypto platforms to proactively report your transactions to HMRC — ending the era in which an investor could assume HMRC simply did not have the data. This guide explains what CARF actually reports, what changes for you, and how it stacks on top of the two HMRC mechanics that already governed UK crypto gains: the Section 104 pool and the capital-gains rates that quietly changed in October 2024. It is an explainer, not tax advice; for your specific position, speak to a qualified UK tax adviser.

What CARF actually is

CARF is the UK implementation of the OECD’s Cryptoasset Reporting Framework — the crypto analogue to the long-standing automatic-exchange regimes for bank accounts, and a close cousin of the EU’s DAC8. The mechanic is simple and consequential: from 1 January 2026, UK-based crypto platforms must collect and proactively report relevant transaction information for UK individuals and entities to HMRC. Where the US reaches the same end through the 1099-DA form issued to each trader, the UK reaches it through direct platform-to-HMRC reporting.

The practical effect is an information shift. Before CARF, HMRC’s visibility into an individual’s crypto activity was patchy — built from data requests, exchange disclosures, and Self Assessment honesty. After CARF, the default assumption flips: for transactions on reporting platforms, HMRC receives the data whether or not you declare it. That does not change what you owe — UK crypto tax law has not changed because of CARF — but it changes the realism of getting it wrong, because mismatches between what a platform reports and what you file become visible to HMRC in a way they previously were not.

What CARF does not change

It is just as important to be clear about what CARF leaves untouched, because a lot of 2026 content blurs this. CARF is a reporting regime, not a new tax. It does not introduce a new crypto tax, change the rate you pay, or alter how a gain is calculated. The underlying rules are the same ones HMRC has applied since it first confirmed in 2018 that crypto assets are property subject to Capital Gains Tax, codified in the HMRC Cryptoassets Manual and TCGA 1992. CARF simply makes those existing obligations harder to ignore.

The rules CARF now makes visible

Three HMRC mechanics govern most UK crypto investors’ gains, and CARF is the reason they suddenly matter to people who previously skated past them.

The Section 104 pool. UK CGT does not treat each coin you buy as a separate lot. Instead, each token type sits in a pooled holding — the Section 104 pool, from TCGA 1992 s.104 — with a single average cost. When you dispose, your gain is proceeds minus the average pooled cost, not the cost of any specific purchase. Two short-window rules sit on top: the same-day rule (s.105) and the 30-day “bed-and-breakfast” rule (s.106A), which override the pool for disposals matched to purchases within those windows. Reconciling a year of activity into the correct pool is the single hardest part of UK crypto tax, and it is exactly what CARF-era accuracy demands. We cover the mechanic in detail in our Section 104 pool guide.

The post-October-2024 CGT rates. This is where a great deal of UK crypto content is now simply wrong. In the Autumn Statement of 30 October 2024, the UK raised CGT rates with immediate effect — from the old 10%/20% (basic/higher rate) to 18%/24%. Any guide, calculator, or back-of-envelope estimate still using 10%/20% is out of date, and a CARF-era investor reconciling against HMRC’s data needs the current figures.

The shrinking annual exempt amount. The CGT annual exempt amount — the gain you can realise tax-free each year — has been cut twice in succession: from £12,300 to £6,000 for 2023/24, then to £3,000 from 2024/25 onwards. The result is that far more ordinary investors now exceed the threshold and must file. If your total gains for the year exceed £3,000, you must report them via Self Assessment, completing the SA108 Capital Gains Summary alongside your SA100.

What to do before your next Self Assessment

For most UK crypto investors, CARF turns a deferrable chore into a now problem. The practical sequence:

1. Pull a complete transaction history from every exchange, wallet, and DeFi protocol you used — not just the platforms you remember, because CARF means HMRC may see activity you have forgotten.
2. Reconcile into Section 104 pools, applying the same-day and 30-day rules. This is where crypto-tax software earns its fee; doing it by hand across multiple venues is where most errors originate.
3. Apply the current 18%/24% rates against gains above the £3,000 annual exempt amount.
4. File the SA108 with your Self Assessment if you exceed the threshold, and keep your reconciliation records — the audit trail that resolves any mismatch with platform-reported data quickly and in your favour.

The tools that handle CARF-era reconciliation

The two UK-focused crypto-tax tools worth an affiliate’s attention both produce HMRC-format reports built around the Section 104 pool and the current rates. Koinly is the market leader for UK crypto tax, with broad exchange and wallet coverage and an HMRC report that handles the pooling and short-window rules. Recap is the UK-incorporated specialist, built around UK rules from the ground up with an end-to-end-encryption privacy posture that resonates in a CARF world where data exposure is front of mind. Either removes the manual-reconciliation burden that CARF has just made unavoidable; our reviews decode the affiliate economics and the product trade-offs of each.

What a mismatch with HMRC now means

The practical risk that CARF changes is the consequence of a discrepancy. Before, an undeclared gain was, in many cases, simply invisible. Now, HMRC can compare the transaction data a platform reports against the gains you declare — and a mismatch is a flag. In recent years HMRC has already run “nudge letter” campaigns to crypto holders it believed had under-declared; CARF gives those campaigns a far richer data source to work from.

The exposure is not hypothetical. Under HMRC’s penalty regimes, an inaccuracy in a return can carry a penalty calculated as a percentage of the tax owed, scaled by whether HMRC judges the error careless or deliberate, and a separate failure-to-notify penalty can apply where chargeable gains were never declared at all. Interest accrues on tax paid late. None of this is new law — what is new is the realism of HMRC noticing. The single best protection is a clean, reconciled record: if your filing matches the platform data, there is nothing to query, and if HMRC does raise a point, a documented Section 104 reconciliation resolves it quickly and in your favour. This is precisely why CARF turns accurate record-keeping from a nicety into the main event.

The international picture: CARF, DAC8, and automatic exchange

CARF is not a UK quirk. It is the UK’s implementation of an OECD framework designed to do for crypto what the Common Reporting Standard already does for bank accounts — establish automatic, cross-border exchange of account and transaction information between tax authorities. The EU’s parallel measure is DAC8, and dozens of jurisdictions are adopting equivalent regimes on similar timelines. The direction of travel is unambiguous: the gap that once let crypto activity sit outside the automatic-exchange net is closing, and an offshore or non-UK exchange is progressively less of a shield than it used to be, because the framework is built to share information across borders. UK content should frame CARF as the local edge of a global shift, not an isolated UK rule.

Common questions

Do I owe new tax just because of CARF?

No. CARF is a reporting regime, not a new tax. You owe exactly what UK CGT and income tax law already required — CARF only makes it visible to HMRC. If you had nothing to declare before, you have nothing to declare now.

What if I used a non-UK or offshore exchange?

CARF’s reporting obligations apply most directly to UK-based platforms, but the broader OECD/DAC8 framework is explicitly designed for cross-border information exchange, so non-UK venues are increasingly within scope of equivalent regimes that share data with HMRC. Treat “I used an offshore exchange” as a reason to reconcile carefully, not a reason to assume invisibility.

Does CARF mean I have to pay tax on crypto I only ever held?

No. Simply holding crypto is not a taxable event in the UK — CGT arises on a disposal (selling, swapping one token for another, spending it, or gifting it other than to a spouse). If you only ever bought and held, there is generally no gain to report, though good records still matter for when you eventually dispose.

Where do staking and DeFi fit?

Staking and certain DeFi returns are generally treated as income at the point of receipt (at market value), and then enter your Section 104 pool at that value for a later CGT calculation on disposal — a two-layer treatment that is easy to get wrong by hand and a strong reason to use software. HMRC’s DeFi guidance continues to evolve, so this is an area to watch and to take adviser input on.

The bottom line

CARF does not raise your tax bill, but it removes the option of hoping HMRC does not notice. For UK crypto investors, 2026 is the year the data becomes symmetric — the platforms report, HMRC receives, and the only variable left is whether your own filing matches. Reconcile properly into the Section 104 pool, use the current 18%/24% rates and the £3,000 allowance, file the SA108 if you exceed it, and keep your records. This guide is general information, not tax advice; for your specific circumstances, consult a qualified UK tax professional or HMRC directly.