Accountants for US and UK Tax: What They Do, What It Costs, and How to Choose One

Rates, thresholds and deadlines on this page were checked against the official US and UK sources linked throughout on 2026-10-01. Tax rules change; confirm anything you intend to act on, or ask us.

Accountants for US and UK tax do one thing ordinary accountants do not: they hold two sets of rules, two tax years and two filing calendars in view at once, and make the answers agree. If you are an American in London, a UK resident with US income, or a business selling on both sides of the Atlantic, you are not looking for one more accountant — you are looking for someone who can make the UK return and the US return tell the same story without either tax authority taking issue.

This guide is written to be useful before you hire anyone: what the work involves month by month, what drives the cost, what CPA, EA, ACCA and ICAEW actually mean, which forms each side needs, when you need two accountants instead of one, and the red flags that should end a conversation.

Who needs accountants for both US and UK tax

Not everyone with a transatlantic life needs a specialist. Those who do fall into five groups.

Americans and dual citizens living in the UK. The United States taxes on citizenship, not residence. The IRS is explicit that a US citizen or resident alien abroad is "subject to tax on worldwide income from all sources" and files under substantially the same rules as someone living in Ohio. The UK taxes on residence. Live in the UK as a US citizen and both systems have a claim on the same income — which is what the US–UK double tax treaty and the foreign tax credit exist to resolve. A UK payslip, a pension, an ISA and a buy-to-let each have to be described twice, in two currencies, under definitions that do not match.

UK residents with US income, US property or a US company. A UK resident holding US rental property, receiving US-source dividends, owning US corporation shares or sitting as a member of a US LLC has US filing exposure and a UK obligation on the same income. LLCs are a particular problem, because the two countries do not agree on what an LLC is — which can break foreign tax credit relief if nobody models it in advance.

Accidental Americans who have only just found out. People born in the United States to non-American parents, or born abroad to an American parent, are frequently US citizens without ever having held a US passport; a bank's FATCA questionnaire is usually how they find out. Our guide to being an accidental American sets out the routes back into compliance.

Businesses operating on both sides. A UK limited company with US customers or contractors; a US corporation opening a UK subsidiary; a founder with equity in both. These raise permanent establishment risk, transfer pricing, withholding, payroll in two systems and two sets of statutory accounts — see US–UK cross-border business tax.

People in the middle of a move. The messiest year is always the year you move. The UK may split the tax year into a non-resident part and a resident part; the US splits nothing, because your citizenship did not change. Getting the timing of a US–UK move right is often worth more than every other planning point combined. If you are unsure which side you are resident on, start with our residency explainer.

Why the US and UK tax years don't line up — and what it changes

This is the structural fact that makes dual filing harder than two separate filings, and most pages skip it. The UK tax year runs 6 April to 5 April — GOV.UK confirms the year just ended started on 6 April 2025 and finished on 5 April 2026 — while the US tax year is the calendar year, 1 January to 31 December. They overlap by about nine months and never by twelve.

One UK tax year straddles two US tax years

A UK year of 6 April 2025 to 5 April 2026 sits inside two US tax years, 2025 and 2026. A single P60 therefore feeds parts of two US returns, and a single Form 1040 draws on parts of two UK years. Four consequences follow.

• Apportionment. UK employment income, PAYE deducted and pension contributions have to be cut at 31 December and allocated across two US years. From an annual P60 alone that is guesswork; from monthly payslips it is arithmetic.
• Credit timing. UK tax must be matched to the US year in which the income falls. A mismatch rarely destroys the relief but can strand it in the wrong year.
• Paid versus accrued. The credit is claimed on either a paid or an accrued basis. Accrued often lines the two systems up better for a UK filer, because UK tax accrues across the UK year rather than landing when HMRC is paid — and the election is effectively sticky once made, so it belongs in the first conversation, not year three. Our comparison of the exclusion and the credit covers which suits which profile.
• Carryovers run on the US clock. Excess credits carry forward in US tax years, so a wrong apportionment means a wrong carryforward for years.

Which return you prepare first

For most people resident in the UK the UK return is prepared first and feeds the US one. The reason is mechanical: the US return needs a UK tax figure to claim credit for, and the UK return needs nothing from the US side. Reverse the order and you estimate the UK liability, file on the estimate, then amend. The order flips where a US liability drives a UK claim, or where a treaty position must be settled before either return can be finalised — both reasons to agree the sequence in the engagement letter rather than in March.

The dual tax-year calendar

Every date below was confirmed against IRS and GOV.UK guidance on the date at the top of this page; dates falling on a weekend or public holiday can shift. We keep a live version on our deadlines page.

Two entries deserve emphasis. 15 April is a payment date, not merely a filing date: the extension to 15 June buys time to file, not time to pay. And 31 January is three obligations at once, which is why a first Self Assessment bill is often around 150% of what people expect — a fortnight after the US fourth-quarter estimate.

What a US–UK accountant actually does, month by month

Most firms sell an annual transaction. The work is a cycle, and its quality is decided long before either return is drafted.

January to April. January is the UK deadline month; a good adviser agreed your figures in November, so January is a payment conversation rather than a data hunt. From February the US year opens as W-2, 1099 and K-1 forms arrive, while UK payslips for the UK year still running are captured monthly so the 31 December cut is real rather than estimated. Foreign account balances are tracked for FBAR and FATCA — the peak balance during the year, not the year-end balance, which is the most common reporting error we see. By 15 April, US tax owed must be paid and the FBAR filed or extended.

April to July. 6 April closes the UK year. The adviser pulls the P60, P11D, dividend vouchers, rental statements, broker reports and pension records, converts what needs converting, and builds the UK computation. Most specialists file Form 4868 before 15 June to reach 15 October, because the UK figures the US return depends on are not final until the UK computation is done. 31 July brings the second UK payment on account.

July to October. The UK return is finalised and its tax figure becomes an input to the US return. Treaty positions are decided and, where required, disclosed. The credit is computed by category rather than in one lump. Pensions, ISAs, share schemes and non-US funds are tested for the reporting they trigger. A dual return that has not started by early September is being rushed, and rushed work across two systems is where errors live.

November to January. The UK return is filed, the 31 January cash requirement is quantified early enough to fund it, and next year is planned while it can still be changed: pension contributions, the timing of a disposal, whether a UK entity still makes sense, whether an ISA is worth holding given its US treatment.

Outside the annual cycle. Some work never fits the calendar: unfiled years, a move, a property sale, an inheritance, a share scheme vesting, a company formation or liquidation, an HMRC enquiry, an IRS notice. These are where one adviser holding both sides genuinely saves money, because the decision is almost always a two-country decision.

What it costs to have both sides handled

This is the question everyone asks and almost nobody answers honestly.

The only official cost figure either government publishes

Neither HMRC nor the IRS publishes a benchmark for what an accountant should charge. The closest thing to an official number is the IRS's own taxpayer burden estimate in the Instructions for Form 1040. Based on statutory requirements as of 1 October 2025, the IRS estimates the average burden for all Form 1040 and 1040-SR filers at 12 hours and $290 per return; about 8 hours and $160 for non-business filers, 71% of returns; and about 21 hours and $610 for business filers, 29%.

Read that carefully, because it is widely misquoted. It is an average out-of-pocket cost, defined to include preparation and submission fees, postage, photocopying and tax software — so it blends people who paid nothing but a software licence with people who paid a professional. The IRS says as much: these costs "vary extensively depending on the tax situation of the taxpayer, the type of software or professional preparer used, and the geographic location". It is a national average for domestic returns, not a quote for a dual filing. There is no UK equivalent: HMRC publishes deadlines and penalties, not fee benchmarks.

Why nobody can quote you honestly from a web page

Every "average accountant fee" table online comes from a private survey or a vendor's own price list — usually undated, and almost never for dual filers. We do not publish a fixed price list for cross-border work for the same reason a surveyor will not price a building from a postcode: the scope is the price, and it is not knowable until someone has read your documents. What we do publish is how the pricing works, on our pricing page. For a figure for your own position, book a consultation.

Why dual filing costs more than two single returns

People reasonably assume a US return plus a UK return should cost roughly the sum of the two. It almost never does, for reasons that are structural rather than commercial.

• The same facts are captured twice, differently. A UK rental is not described the same way on an SA105 as on a Schedule E: depreciation, mortgage interest relief and what counts as a repair all diverge. One property becomes two computations, not one used twice.
• Two currencies, with rules about which rate. The IRS requires US returns to be expressed in US dollars, generally at the rate prevailing when the item is received, paid or accrued — a per-transaction discipline, not a year-end conversion.
• The two years must be reconciled. A UK year is cut and apportioned across two US years — real work, completely invisible in the finished return.
• Relief has to be modelled, not just claimed. Whether the exclusion, the credit or a combination wins, and whether the credit is claimed paid or accrued, takes several runs.
• Positions must be consistent, and reviewed twice. What you claim on the UK return constrains the US return and vice versa, and each position needs review by someone qualified in that system before sign-off.

A useful mental model: the second return is not a copy, it is a translation — and translation costs more than transcription.

What moves your fee, up and down

In rough order of impact: records quality, by a distance the biggest factor — uncategorised bank statements, missing broker reports, no record of which payslip belongs to which month, all of it chargeable time. Then the number of income streams, each adding a computation on both sides. Then property, which adds a UK property page, a US schedule and a depreciation history the US requires and the UK does not. Then capital gains, two disposal regimes with different reliefs. Then self-employment or a company, each bringing its own returns and, for US persons, potentially Form 5471 or Form 8621 territory. Then a move during the year, rushed work, and finally unfiled years, priced per year rather than as one job.

Pulling the other way: clean bookkeeping the adviser can access directly, a complete document set given once, engaging early in the cycle, and stability — the second year is cheaper once the analysis, elections and carryforwards exist.

Catch-up filing is a different conversation

If you have unfiled years you are not buying a tax return, you are buying a remediation project. The IRS Streamlined Filing Compliance Procedures require a defined set of back years plus a certification that the failure was non-wilful, and the cost turns on how many years there are and how complete the records are. Missing FBARs have their own delinquent filing route. Neither should begin before a licensed professional has assessed eligibility.

What a fixed fee should and shouldn't include

Ask for this in writing. A well-drawn fixed fee for a dual filer normally includes the agreed returns and schedules, the credit or exclusion computation, one round of questions, e-filing where available, and a copy of everything filed. It normally excludes forms discovered mid-engagement (a foreign trust, a non-US fund, an unreported company interest), amendments to prior years, correspondence with HMRC or the IRS after filing, planning as distinct from compliance, and any year you have not engaged them for. Firms reasonably differ on where that line sits. What matters is that it exists and that you can see it before you sign.

CPA, EA, ACCA or ICAEW — which credential do you actually need?

Almost every page in this market either ignores credentials or uses "dual qualified" without saying by whom. Here is what the four designations are, taken from the bodies that award them.

CPA — Certified Public Accountant (United States)

A CPA is licensed by an individual US state board of accountancy, not federally — there is no single national CPA licence. Licensure requires passing the Uniform CPA Examination together with education and experience requirements set by that state, and the routes in have been changing state by state in recent years. Because the licence is issued by a state, it can be checked with that state's board.

EA — Enrolled Agent (United States, federal)

The IRS defines an enrolled agent as "a person who has earned the privilege of representing taxpayers before the Internal Revenue Service", either by passing a three-part IRS examination covering individual and business returns or through experience as a former IRS employee. The IRS describes it as "the highest credential the IRS awards".

Two features matter here. EAs have unlimited practice rights: the IRS states they are "unrestricted as to which taxpayers they can represent, what types of tax matters they can handle, and which IRS offices they can represent clients before" — the same representation standing as attorneys and CPAs. And it is a federal credential, not tied to one state. Enrolled agents complete 72 hours of continuing education every three years and are governed by Treasury Circular 230.

ACCA — Chartered Certified Accountant (United Kingdom)

The UK Government's regulated professions register lists "Chartered Certified Accountant (ACCA/FCCA)" as a protected title regulated by the Association of Chartered Certified Accountants, with reserved activities of statutory audit, other audit activities, reporting under ATOL, and solicitors' accounts. The letters are ACCA for a member and FCCA for a fellow, and a member running a UK practice must also hold a practising certificate.

ICAEW and the ACA — Chartered Accountant (United Kingdom)

A separate body awarding a separate designation. ICAEW members are ICAEW Chartered Accountants, recognised by the letters ACA or FCA. ICAEW makes the underlying point bluntly: legally, anyone can call themselves an accountant without qualifications, training or experience — it is the chartered designation that has a body standing behind it. ICAS and Chartered Accountants Ireland also confer the title.

Two titles that are not interchangeable

"Chartered Certified Accountant" (ACCA/FCCA) and "Chartered Accountant" (ACA/FCA, or the ICAS and Irish equivalents) are different protected designations, awarded by different bodies. An ACCA member is accurately described as ACCA-qualified, an ACCA member, or a Chartered Certified Accountant — and is not a Chartered Accountant. A firm using "chartered" without naming a body is a question worth asking, not a qualification.

Why there is no single "dual-qualified US–UK" licence

There is no transatlantic accountancy licence. A CPA licence comes from a US state board; enrolled agent status from the IRS; ACCA and ICAEW membership from UK bodies with their own examinations and practising rules. So "dual qualified" means one of two things: one individual has separately earned two credentials, or the firm pairs a US-credentialed person with a UK-credentialed one. Both are legitimate; neither is a single licence, and it is fair to ask which you are being offered.

Which forms each side needs

Form numbers are where dual filing becomes concrete, and most pages in this market list the US forms while naming almost none of the UK ones. Fuller lists sit at US forms and UK forms.

Two rows deserve a warning. Form 8621 is why an ordinary UK fund or investment trust can create disproportionate US reporting, and it catches many Americans in the UK who believed they were investing conservatively. And there is no UK filing extension: 31 January is fixed, with penalties starting at an initial £100, then £10 a day up to £900 after three months, and further penalties at six and twelve months of 5% of the tax due or £300, whichever is greater. Late payment carries separate 5% penalties at 30 days, six months and twelve months, plus interest.

Bookkeeping versus accounting — and why it matters more across two countries

Bookkeeping is the record: every transaction captured, dated, categorised and supported by a document. Accounting is what gets built from it — statements, computations, returns, and the judgements inside them. Bookkeeping answers "what happened"; accounting answers "what does it mean and what do we owe".

For a domestic filer, weak bookkeeping is annoying. For a dual filer it is expensive, because one record has to answer three questions at once: what happened between 6 April and 5 April, for HMRC; what happened between 1 January and 31 December, for the IRS; and what each item was worth in US dollars when it was received, paid or accrued. A ledger built only for the UK year cannot be cut at 31 December without returning to source documents; a ledger kept only in sterling cannot produce a US return without a transaction-by-transaction conversion. One capturing date, amount, category and the rate at the time answers all three.

That is the honest link back to cost. When records are incomplete the adviser is not doing tax work — they are doing forensic reconstruction, at professional rates, under deadline pressure, twice. It is why identical facts produce very different fees at two firms, and why the cheapest way to cut a cross-border fee is almost never to negotiate the rate. It is to arrive with clean books.

Do you need one accountant or two?

Every firm's answer to this is "use us for both". That is not always true.

When one coordinated firm is right

One firm holding both sides is usually right where the facts are shared and the positions interact: a US citizen employed in the UK; a dual citizen with UK pensions and US investments; a UK resident with a US rental; a founder with a company in one country and residence in the other. The advantage is real — one data set, one view of the treaty position, one person accountable if the returns disagree, and no fee paid twice for the same review.

When you genuinely need two

• A contentious enquiry on one side. An HMRC enquiry or an IRS examination is adversarial work with its own discipline. You want a specialist in that jurisdiction leading, with the other adviser supporting.
• A statutory audit requirement. Audit is a reserved activity with its own registration, so it is a separate appointment — and independence rules may bear on who else can do what.
• US state-level controversy. State tax is its own world; a federally focused adviser may not be right for a California or New York residency dispute.
• Legal privilege. Where a position may become litigious, the advice may need to sit with lawyers rather than accountants, particularly on the US side.
• Complex trusts and estates. The UK and US treat trusts so differently that specialist input on each side is usually cheaper than one firm learning on your file.

Our note on choosing an accountant for a cross-border business applies the same test to companies.

How a coordinated engagement should work

If you use two firms, insist on three things in writing: who owns each return, who agrees the shared positions (residence, treaty claims, the credit basis), and who resolves a disagreement. Left unmanaged, two competent advisers can produce two defensible returns that contradict each other — and you sign both.

How to choose — and the red flags

Questions to ask before you engage

• Who prepares each return, and who signs it off? A name and a credential, for each side.
• What is in scope and what is extra? Ask for the exclusions list, not just the inclusions.
• Which return do you prepare first, and why?
• Will you claim the credit on a paid or an accrued basis, and what does that commit me to later?
• If HMRC or the IRS writes to me after filing, is dealing with it included?
• What professional indemnity cover do you hold, and who supervises you for anti-money laundering?

Red flags on the US side

The IRS publishes its own guidance, and it is more specific than most firms' "how to choose" pages. From Topic no. 254 and the IRS's choosing a tax professional page:

• No PTIN. "Paid tax return preparers must have a PTIN to prepare all or substantially all of a tax return."
• Won't sign. Use a preparer "who enters his or her PTIN on the tax return, signs the tax return, and provides you a copy of the return". One who does the work and leaves the signature block empty — a ghost preparer — is a serious warning sign, and you are left responsible for what was filed.
• A fee based on a percentage of the refund. Avoid preparers "who base their fees on a percentage of the refund".
• Your refund into their account. Also on the IRS's avoid list: preparers "who offer to deposit all or part of your refund into their financial accounts".
• A refund promised before they have seen anything. "Be wary of tax return preparers who claim they can obtain larger refunds than others can." Good preparers "will ask to see your records and receipts".
• A blank or incomplete return to sign. The IRS is unambiguous: "Never sign a blank tax form."
• Nobody there in July. Consider "whether the individual or firm will be around for months or years after filing the return". Cross-border returns generate correspondence; a seasonal operation cannot answer it.

Red flags on the UK side

• No professional body membership they can name. "Accountant" is not a protected title in the UK. ACCA, ICAEW, ICAS, Chartered Accountants Ireland, ATT and CIOT membership can each be checked with the body itself.
• No anti-money laundering supervision. Accountancy service providers must be supervised — by a professional body, or by HMRC where no body supervises them. It is not optional.
• Not registered with HMRC as a tax adviser. This is new, and most buyers do not know it. Registration became mandatory for paid tax advisers who interact with HMRC on clients' behalf from 18 May 2026, in stages through to 31 March 2027. HMRC's registration conditions require evidence of anti-money laundering supervision, and that the business has no "relevant outstanding tax returns or unpaid tax", is not "subject to an anti-avoidance sanction or a stop notice", has no "relevant, unspent convictions for fraud or tax offences", and is not "formally insolvent".
• No professional indemnity insurance, no engagement letter, or vagueness about who signs. If nobody will name the person who reviews and signs your return, that is your answer.

Credential red flags

Watch for designations that name no body. "Certified in the US and UK", "international tax experts" or a bare "dual-qualified" mean nothing on their own — they are awarded by nobody and cannot be checked. Ask which body, which designation, which member, then verify it. A firm confident in its credentials will give you the name.

How to verify a professional yourself

In the United States, the IRS Directory of Federal Tax Return Preparers with Credentials and Select Qualifications lists preparers holding credentials the IRS recognises; a CPA licence can be checked with the issuing state board, and enrolled agent status with the IRS Office of Enrolment. In the UK, check membership directly with ACCA, ICAEW, ICAS, Chartered Accountants Ireland, ATT or CIOT.

When software or DIY is genuinely fine

If your position is simple on one side and effectively non-existent on the other — a US citizen in the UK on PAYE only, no property, no self-employment, no investments beyond a current account below the FBAR threshold, no share schemes — consumer software plus care may be enough, and our calculators will give you a sense of the numbers first.

It stops being fine at recognisable points: a rental property, a non-US fund, a share scheme, self-employment or a company, a move during the year, an inheritance, any unfiled year, or any letter from HMRC or the IRS. At those points the cost of getting it wrong exceeds the fee, usually by a wide margin.

Working with Next Tax Source

We prepare US, UK and cross-border filings for individuals, families and businesses. Every filing is reviewed and signed off by a licensed human professional: a licensed CPA or Enrolled Agent on the US side, and an ACCA-qualified accountant on the UK side. Nothing goes to HMRC or the IRS without that review and your own sign-off.

For the narrower service pages, see US–UK expat tax accountants for individuals or US–UK cross-border business tax for companies. Our process page sets out how an engagement runs. When you want a figure rather than a range, book a consultation and we will scope it properly.

This page is general information, not advice. Rates, thresholds and deadlines change; the figures here were verified against the official sources cited on the date shown above. Confirm your own position with a qualified professional before acting on it.