US personal tax services for a high-net-worth individual mean the preparation of the annual Form 1040 plus every schedule, information return, state filing, estimate and disclosure that hangs off it — together with the planning and representation that stop the return being merely a record of tax you could have avoided. The 1040 itself is the smallest part of the work. For a client with investment accounts, equity compensation, a business interest or a life split between the US and the UK, the value — and the risk — sits in everything attached to it.
This guide sets out what a properly scoped 2026 engagement includes, what the cheap quote leaves out, how fees are structured, and the specific additions that matter when the client is an American living in the United Kingdom.
What US personal tax services actually cover
A complete engagement has four layers. First, compliance: the federal Form 1040 with its supporting schedules — Schedule B for interest and dividends, Schedule C for self-employment, Schedule D and Form 8949 for capital gains, Schedule E for rental and partnership income, and Schedule 2 for additional taxes such as the alternative minimum tax and the 3.8% net investment income tax. Second, disclosure: the international information returns described below, which carry the largest penalties in the personal tax system. Third, payments: safe-harbour estimated tax calculations across the year so April brings no penalty and no surprise. Fourth, advice and defence: planning before transactions and representation if the IRS asks questions afterwards.
A quote that covers only layer one is not a smaller version of the same service — it is a different service. Most of the expensive failures we repair at TaxStone began as a competent 1040 with a missing information return behind it.
The 2026 filing calendar the engagement is built around
For the 2025 tax year filed in 2026, the baseline federal deadline was 15 April 2026. Americans whose tax home is abroad receive an automatic extension to 15 June, and anyone can extend to 15 October by filing Form 4868 — an extension of time to file, never of time to pay, as the IRS sets out on its when-to-file page. Taxpayers abroad can request a further discretionary extension to 15 December by letter.
Around those anchors sit the quarterly estimated tax dates (15 April, 15 June, 15 September, 15 January), state deadlines that do not always match the federal ones, and — for anyone with foreign accounts — the FBAR, due 15 April with an automatic extension to 15 October. A good firm runs this calendar for you; you should never be the one remembering dates.
The information returns: where the real penalties live
For a high-net-worth client, the disclosure layer is the engagement. Each of these forms is triggered by facts, not by tax due — you can owe nothing and still owe a five-figure penalty for a missed form:
- FBAR (FinCEN Form 114) — required once aggregate foreign account balances exceed $10,000 at any point in the year; penalties for non-wilful failure run to five figures per year, as described in the IRS's FBAR guidance.
- Form 8938 (FATCA) — foreign financial assets above $200,000/$300,000 for single filers living abroad ($400,000/$600,000 married filing jointly); $10,000 baseline penalty for failure.
- Form 5471 — interests in foreign corporations, including an ordinary UK limited company; $10,000+ per form per year, with GILTI and Subpart F calculations attached.
- Form 8621 — passive foreign investment companies (PFICs), which is what most UK funds, ISAs holding funds, and investment bonds are in US eyes.
- Form 3520 / 3520-A — foreign trusts and large foreign gifts or inheritances; penalties start at the greater of $10,000 or a percentage of the amount involved.
- Forms 8833, 1116, 2555 — treaty positions, foreign tax credits and the foreign earned income exclusion, which for the 2026 tax year shelters up to $132,900 of earned income.
State returns: the layer people forget they still have
Moving abroad does not automatically end a state filing obligation. Aggressive states — California, New York, Virginia, New Mexico among them — treat domicile as continuing until it is affirmatively broken, and part-year moves, retained property, or a driving licence renewed for convenience can keep a state return alive for years. An HNW engagement should include a state residency review in year one and the state returns themselves for as long as they are genuinely required, plus the paper trail that supports non-residency when a state audits it. Our guide to state taxes for Americans abroad covers the domicile rules state by state.
Estimated taxes and safe harbours: managing the year, not the deadline
High-net-worth income arrives unevenly — bonuses, RSU vests, capital gains, carried interest, business distributions — and the US taxes it on a pay-as-you-go basis. The engagement should include quarterly safe-harbour calculations (generally 110% of the prior year's tax for higher earners) so that underpayment penalties never arise, with recalculation after any liquidity event. You can sanity-check your own position with our US federal income tax calculator and our estimated tax calculator, but in a properly run engagement the firm sends you the voucher amounts before each deadline without being asked.
Planning: the part that pays for the engagement
Compliance records history; planning changes it. In a 2026 HNW engagement the planning layer typically covers: the FEIE-versus-foreign-tax-credit election and when to switch; harvesting or deferring capital gains around the 3.8% net investment income tax; Roth conversion windows in low-income years; charitable structuring, including dual-qualified giving for donors with UK ties; equity compensation timing across calendar years; and entity questions — whether a consulting business should be a sole proprietorship, an S corporation or, for a UK resident, deliberately neither.
The test of a real planning relationship is simple: does the firm contact you before year-end with numbers, or do you only hear from them in March? By the time the return is being prepared, almost every planning door for that year has closed.
Representation: who stands between you and the IRS
IRS notices are a statistical certainty over an HNW client's filing life — matching notices, penalty assessments, occasionally a full examination. Only three credentials carry unlimited rights to represent you before the IRS: attorney, CPA and Enrolled Agent. An engagement with a firm that lacks representation rights means that when a notice arrives, you are hiring a second firm at exactly the moment you have least leverage. Ask up front who signs the Form 2848 power of attorney and what notice-handling is included; our IRS representation service is built into TaxStone engagements rather than sold as an emergency add-on.
What the cheap quote leaves out
The US tax preparation market quotes anywhere from a few hundred dollars to five figures for "the same" return, and the difference is almost always scope. A budget preparer prices the 1040 and treats everything else as an extra: each Form 5471 billed separately at hourly rates, FBAR "available on request", state returns excluded, no estimates, no planning call, no notice handling. The headline price is low because the service has been hollowed out.
The failure mode is predictable. The preparer never asks whether your UK ISA holds funds (PFICs), never asks about the UK limited company you own 30% of (Form 5471), never asks about the inheritance from a British grandparent (Form 3520). Nothing goes wrong until a FATCA data feed or a bank letter surfaces the gap — and then the cost is not a form fee but a penalty-exposed disclosure exercise that dwarfs a decade of proper preparation fees.
How fees actually work in 2026
Market surveys put a simple itemised federal-plus-state return in the $250–$800 range with mainstream CPA firms, while genuinely complex personal work — multi-entity, multi-state, international — runs from roughly $1,000 to $7,500 and beyond. For cross-border HNW returns, fixed-fee scoping has largely replaced open hourly billing at reputable firms: you should see a schedule listing the 1040, each information return by form number, each state, the FBAR, estimates and a defined planning allocation, with a stated rate for anything discovered mid-engagement.
Treat any quote that cannot itemise its scope as unpriceable rather than cheap. The correct comparison between two quotes is never the bottom line; it is the list of forms each one commits to filing.
EA, CPA or attorney: who should do the work?
All three can prepare and represent. The practical differences: CPAs are state-licensed and strongest where audited financials and state practice matter; Enrolled Agents are federally licensed specifically in taxation, examined by the IRS itself, and carry the same unlimited representation rights; attorneys add privilege where wilfulness or litigation is in play. For cross-border personal work, the credential matters less than the pairing — a US-qualified preparer working alongside a UK-qualified one inside the same engagement. Our comparison of ACCA-qualified accountants and Enrolled Agents explains why the combination beats either alone.
The UK layer: what changes when the client lives in Britain
For an American in London, the US engagement cannot be scoped in isolation. The UK taxes the same income on a different tax year (6 April to 5 April), which makes foreign tax credit timing a craft of its own; UK pensions need treaty positions rather than default reporting; UK investment accounts are PFIC minefields; and the interaction between UK payments on account and US estimates determines which country's tax is creditable when. A US-only firm and a UK-only firm, each competent, will still jointly produce a worse outcome than one firm computing both returns together — because every planning move in one country shifts the numbers in the other.
That interaction is TaxStone's entire practice: US Enrolled Agents and UK ACCA-qualified accountants inside one engagement, one data collection, one coordinated pair of returns. Start with our overview of US tax filing for Americans in the UK, or contact us with your current scope list and we will tell you what is missing from it.
A scoping checklist to take into any first meeting
Use this list to force any prospective firm — including us — to commit to scope in writing:
- Which information returns are included by form number, and what does each additional one cost?
- Are FBAR and Form 8938 filed as standard, and who gathers the account data?
- Which state returns are included, and will you review whether my state filing obligation has genuinely ended?
- Are quarterly estimated tax calculations and vouchers included across the year?
- Is there a named point of contact with representation rights who handles IRS notices, and is notice response included?
- Is there a pre-year-end planning review with numbers, and is it in the fixed fee?
- If I live abroad: who handles the other country's return, and do the two sides share a workflow?
