Crypto Asset Reporting Framework UK: Dual Filer's Guide

The Crypto Asset Reporting Framework UK took effect on 1 January 2026. UK reporting cryptoasset service providers are collecting user and transaction data now, will file their first report to HMRC by 31 May 2027 covering calendar year 2026, and that data will be exchanged internationally from 2027. The year being reported is the year you are living in.

The point most commentary misses: the first reported year is already running

Almost every article written about CARF frames it as a future obligation on exchanges. For the US-UK dual filer, that framing is wrong in a way that matters. The framework does not begin to bite when the first report lands at HMRC in 2027. It began to bite on 1 January 2026, because that is the date from which the underlying record started being written.

Your exchange is, at this moment, capturing your tax residence, your taxpayer identification numbers, and a transaction-level record of your 2026 activity. That record will be transmitted whether or not you take any action, and it describes a period that is already partly in the past. You cannot amend it, curate it, or reconcile it retrospectively. You can only ensure that what you have filed, and what you will file, is consistent with it.

That is why this is a compliance and disclosure question rather than a filing question. If your UK or US returns for earlier years already reflect your cryptoasset positions accurately, CARF is an administrative event and nothing more. If they do not, the arrival of a standardised, machine-matchable dataset covering the same holdings is the point at which the discrepancy becomes visible — and the correct response is a considered disclosure through the proper channel, not a change of filing behaviour going forward. Jungle Tax works with dual filers on exactly this distinction.

What is the Crypto Asset Reporting Framework?

CARF is an OECD-designed transparency standard, structurally modelled on the Common Reporting Standard that has governed bank account exchange since 2016. It requires Reporting Cryptoasset Service Providers (RCASPs) to identify their users, determine each user's jurisdiction or jurisdictions of tax residence, and report annual transaction data to their home tax authority, which then exchanges it with the authorities of the jurisdictions where the users are resident.

More than fifty jurisdictions have committed to implementation, with the UK among the earliest movers. The UK's rules sit in the Cryptoasset Service Providers (Due Diligence and Reporting Requirements) Regulations 2025 and are explained in HMRC's International Exchange of Information Manual. HMRC's own commencement guidance confirms the start date and the reporting deadline: see IEIM8000050 — Commencement.

Which providers are in scope?

• Centralised exchanges — the mainstream venues where most HNW holdings sit.
• Custodial wallet providers — including institutional custody arrangements.
• Brokers and dealers in cryptoassets, including those executing on behalf of clients.
• Certain DeFi arrangements, where a controlling entity can be identified and is treated as exercising sufficient control over the service.
• Certain payment processors and intermediaries facilitating exchange transactions.

The nexus rules matter for anyone with a portfolio spread across venues. A provider is in the UK net if it is UK tax resident, incorporated or managed in the UK, has a UK branch, or has a regular place of business here. But a non-UK provider is not thereby outside the system — it will be reporting to its own CARF-implementing jurisdiction, which will exchange the data onward to HMRC and, under the parallel arrangements, to the IRS. The practical planning assumption for a sophisticated holder should be that any custodial venue in a cooperative jurisdiction is a reporting venue.

What data is actually collected?

The dataset is deliberately richer than a simple year-end balance. Broadly, an RCASP collects and reports:

• Name, address, date of birth, and jurisdiction(s) of tax residence.
• Tax identification numbers for each jurisdiction of residence — for a US-UK dual filer, that typically means both a US TIN and a UK National Insurance number or UTR.
• For entity users, the entity details and, where the entity is passive, the controlling persons behind it.
• Transaction data by cryptoasset type: exchanges between cryptoassets and fiat, exchanges between cryptoassets, and transfers — including retail payment transactions above a de minimis threshold.
• Aggregate gross amounts paid and received, unit counts, and the number of transactions, split by transaction type.
• Transfers to unhosted or self-hosted wallet addresses, which are reported even though the destination itself is outside the framework.

That final point deserves emphasis. A common assumption is that moving assets to self-custody removes them from view. It does not remove the movement from view. The outbound transfer is itself a reportable data point on the exchange side, and the resulting picture — assets acquired on a reporting venue and withdrawn to a private address — is more conspicuous than a static custodial holding, not less.

The UK timeline, precisely

Date	What happens
1 January 2026	UK CARF commences. RCASPs begin due diligence and data collection on all users.
1 Jan – 31 Dec 2026	The first reportable period. This is the calendar year currently running.
31 January 2027	UK RCASPs must be registered with HMRC.
1 Jan – 31 May 2027	First reports submitted to HMRC covering calendar year 2026.
During 2027	First international exchanges of CARF data between participating tax authorities.
31 May 2028 and annually	Subsequent reports, each covering the prior calendar year.

Note the mismatch that catches UK residents out. CARF reports on a calendar year. The UK tax year runs 6 April to 5 April. A CARF report for calendar 2026 therefore straddles the 2025/26 and 2026/27 UK tax years, and any reconciliation exercise has to be built to bridge that gap rather than assuming the periods align. US filers, who report on the calendar year, will find the CARF period maps cleanly to their Form 1040 — which cuts both ways.

How does the US side of the same holding get reported?

This is where generalist UK crypto content becomes unhelpful for our reader, because it treats CARF as the whole story. For a US person resident in the UK, or a UK resident with US citizenship, the same wallet or exchange account is simultaneously exposed to three distinct US reporting mechanisms, each with different scope and different triggers.

1. Broker reporting on Form 1099-DA

The US introduced its own custodial broker reporting regime for digital assets. Brokers report gross proceeds for dispositions from 1 January 2025, with cost basis reporting phasing in from 1 January 2026. The IRS sets out the scope, the covered broker categories and the transitional relief on its Digital Assets guidance page.

Two features of 1099-DA reporting create predictable friction for cross-border holders. First, in the early years cost basis is frequently absent or incomplete, particularly where assets have moved between venues, chains or wallets — which means the gross proceeds figure reported to the IRS can look dramatically larger than the actual gain. Second, a form is not the trigger for the obligation. US persons must report disposals and income regardless of whether any broker issues a form, and non-US venues that fall outside the US broker definition will issue nothing at all while still reporting the same activity to HMRC under CARF.

2. FBAR (FinCEN Form 114)

The treatment of exchange-held cryptoassets under FBAR has been in an unsatisfactory holding pattern for years. FinCEN signalled an intention to amend the regulations to bring virtual currency accounts at foreign financial institutions expressly within the FBAR definition, and that amendment has been pending rather than complete. In the meantime a great many practitioners take the protective view and report foreign-custodied crypto accounts.

Where the analysis is considerably less ambiguous is the mixed account. If a foreign exchange account also holds fiat currency, or the relationship sits alongside a foreign bank or e-money account used to fund it, the fiat element is a foreign financial account on ordinary principles and the aggregate $10,000 threshold applies. Valuation for FBAR purposes uses the maximum value during the calendar year, not the year-end figure — a point that materially changes the answer in a volatile asset class. The current instructions and thresholds are on the IRS's Report of Foreign Bank and Financial Accounts page.

3. Form 8938 (FATCA)

Form 8938 casts a wider net than FBAR, reaching specified foreign financial assets rather than only foreign accounts. Foreign-held digital assets and accounts at non-US platforms fall within the intended scope, and the thresholds for taxpayers living abroad are substantially higher than the domestic ones — which is precisely why they are so often misjudged by clients who assume "living abroad" means "exempt". The form's scope and thresholds are set out at About Form 8938. Filing an FBAR does not satisfy Form 8938, and filing Form 8938 does not satisfy the FBAR; where both apply, both are required.

US vs UK: the same holding, two reporting systems

Feature	UK — CARF / HMRC	US — 1099-DA, FBAR, Form 8938
Who reports	The service provider (RCASP)	The broker reports 1099-DA; the taxpayer reports FBAR and 8938
Period	Calendar year (1 Jan – 31 Dec)	Calendar year for all three
First period	2026	2025 for gross proceeds; 2026 for basis
What is captured	Identity, TINs, gross amounts, unit counts, transaction counts, transfers to unhosted wallets	1099-DA: proceeds and (from 2026) basis. FBAR/8938: account existence and value
Non-domestic venues	Reached via exchange with other CARF jurisdictions	Non-US venues generally issue no 1099-DA, but the account may be FBAR/8938 reportable
Self-custody	Not directly reported, but transfers out are	Not directly reported; taxpayer disclosure obligations still apply
Threshold	No de minimis on the core account reporting	FBAR $10,000 aggregate; 8938 thresholds vary by residence and filing status
Character of the obligation	Third-party information reporting	Mixed: third-party plus self-reporting

Why an unreported holding is now a disclosure question

The logic is straightforward once the timeline is understood. Information reporting regimes work retrospectively. The report filed in May 2027 describes the calendar year 2026 as it happened. It will also, for most holders, describe balances that were carried into 2026 from earlier years — because an opening position is itself evidence of prior acquisition. A dataset showing a substantial holding at the start of the first reported year invites the obvious question about when and how it was acquired, and whether that acquisition and any intervening disposals were reported.

So the exposure created by CARF is not primarily about 2026. It is about the years before 2026 that the 2026 dataset implies. Those years are closed. Their returns are filed or not filed. Nothing about future filing behaviour changes what they contain. The only mechanism that addresses a historic gap is a formal correction or disclosure, made on the taxpayer's initiative, through the route appropriate to the facts.

The correction routes, in outline

• UK. HMRC operates disclosure facilities for unreported income and gains, and has run cryptoasset-specific nudge and disclosure activity since 2024. Which facility applies depends on the behaviour behind the omission — careless, deliberate, or reasonable care taken — and that classification drives the penalty range and the number of years assessable. HMRC's cryptoasset positions are set out across the Cryptoassets Manual.
• US. Where the omission was non-wilful, the streamlined filing compliance procedures remain the principal route for taxpayers resident outside the United States, covering delinquent returns and information returns together. Where the facts do not support a non-wilful certification, the analysis is materially different and requires specialist counsel before anything is filed. Our IRS streamlined filing team assesses which route the facts actually support.
• Sequencing. For a dual filer the two exercises are not independent. Gains recognised in a UK disclosure will usually have a US counterpart, foreign tax credit positions have to be recomputed across the affected years, and the information returns (FBAR, 8938) have to be brought into line with whatever the corrected UK position shows. Running one side without modelling the other is the single most common failure we see.

Where the two datasets will disagree — and why that is the real risk

Discrepancy, not concealment, is what generates most enquiry activity. For a dual filer, several structural mismatches are close to guaranteed:

• Gross proceeds versus gain. A CARF report and a 1099-DA both describe gross amounts. Neither describes your gain. A holder who traded actively within a portfolio of stable overall value can generate reported gross figures many multiples of the net position.
• Pooling versus lot identification. The UK applies share-pooling principles with same-day and 30-day rules to cryptoassets; the US applies its own basis identification conventions. The same disposal produces two different gain figures computed on two different bases, in two different functional currencies. That is a legitimate outcome, not an error — but it needs to be documented as such.
• Currency. Sterling and dollar computations of the same transaction diverge, and the divergence compounds across a year of activity.
• Period straddle. The calendar-year CARF report cuts across two UK tax years, so no single UK return will ever tie directly to a single CARF report.
• Transfers read as disposals. Movements between your own venues and wallets appear in the transaction data. Without a maintained internal record demonstrating common ownership, they are indistinguishable from disposals in the reported dataset.
• Staking, lending and wrapping. Several categories currently sit in reporting exceptions or unsettled treatment on the US side while being economically significant on the UK side.

None of these is resolved by the reporting systems themselves. They are resolved by the taxpayer holding a reconciliation that explains, transaction by transaction, why the reported gross figures and the filed positions differ. Building that record is the substantive work, and it is materially easier to build while the venues still hold the underlying data.

Penalties on the provider side — and what they signal

The UK penalty regime for RCASPs includes charges for failure to register, failure or lateness in submitting reports, inaccurate or incomplete reports, and due diligence failures, assessed both at entity level and on a per-user basis. The commercial consequence is entirely predictable: providers will be conservative. Where a user's self-certification is missing, stale or inconsistent, the provider's incentive is to press for correction and, failing that, to report on the most cautious basis available — which for a dual filer typically means reporting to both jurisdictions.

If your exchange has contacted you during 2026 asking you to confirm tax residence or supply a TIN, that is the due diligence process operating. The response you give is the input to a report you cannot later revise, and an inaccurate or evasive self-certification carries its own consequences quite apart from the underlying tax position.

What a dual filer should have assembled

• A complete inventory of custodial venues, including closed accounts and legacy platforms, with the jurisdiction of each provider identified.
• Self-certifications reviewed for accuracy — particularly dual residence, which must be stated correctly rather than simplified to one country.
• A full transaction history exported from each venue, secured independently of the platform. Exchange history access has repeatedly proved fragile.
• A wallet-address map evidencing common ownership of self-custodied addresses, so that transfers can be demonstrated not to be disposals.
• Parallel UK and US gain computations for each affected year, with the basis conventions and currency treatments documented.
• An assessment of FBAR and Form 8938 positions for every year in scope, not only the current one.
• A clear-eyed view of which historic years are complete and which are not — before any correspondence arrives.

For the wider mechanics of how cryptoassets are taxed on both sides of the Atlantic, including pooling, disposals and income characterisation, see our companion guide on crypto and digital assets for US-UK dual filers. This guide deliberately goes deeper on CARF alone; that one covers the underlying computational rules.

Where this leaves the sophisticated holder

The Crypto Asset Reporting Framework does not change what was always true: cryptoasset gains and income have been taxable and reportable in both jurisdictions for years. What it changes is verifiability. Until now, the compliance position of a private crypto portfolio was largely a matter of self-assertion. From the 2026 calendar year, it is a matter of record — a standardised, cross-checked, internationally exchanged record produced by third parties with a penalty-backed incentive to get it right.

For holders whose filings are already complete and accurate, that is a non-event. For holders with historic gaps, the framework does not create the exposure — it removes the obscurity that was concealing it. The distinction between those two positions is worth establishing deliberately, with advisers who can compute both sides, rather than discovering it from correspondence. Our private client team and US-UK specialists handle these reviews as a single integrated exercise.

Speak to us in confidence

If you hold cryptoassets on any custodial venue and file in both the United States and the United Kingdom, the sensible step is a structured review of your historic position while the underlying data is still retrievable and any correction remains entirely on your own initiative. We assess what has been reported, what the 2026 dataset will show, and where the two diverge — then advise on the appropriate disclosure route in each jurisdiction. To discuss your position privately, contact our cross-border team for a confidential consultation. Every conversation is protected, and no engagement is required to have it.