US/UK Tax Advice for American Wealth Managers with British Clients

Become the Trusted Cross-Border Financial & Wealth Advisor Your British Clients Deserve

Protect Your British Clients from £300,000+ Penalties While Building a Reputation as the Go-To US-UK Financial Investment Expert

Following the Finance Act 2024, the UK moved to residence-based inheritance tax and clarified cross-border pension taxation from April 2025. If you’re a US CPA, Enrolled Agent, fiduciary planner, or wealth manager serving clients with British origins, pensions, or investments, these regulatory shifts create both risk and opportunity. Your British clients need you to navigate complex timing, remittance, and reporting challenges that most advisors struggle to understand.

Right now, you face a critical choice. You can refer these valuable clients elsewhere, admitting you lack the specialised knowledge they need. Or you can partner with experts who work behind the scenes, empowering you to confidently serve these clients while protecting them from costly compliance failures.

The Challenge You & Your Clients Are Facing

Your British clients living in the US maintain UK pensions, ISAs, and property interests, creating a maze of dual-jurisdiction tax obligations. You know these clients are valuable, but you also recognise the unique complexity they bring. Reconciling HMRC reporting with IRS obligations requires balancing foreign tax credits, PFIC filings, and domicile-based IHT rules that change annually.

When you misunderstand UK remittance rules, overstate US income, or underreport foreign assets, your clients face severe consequences. Willful FBAR violations carry penalties of $165,353 or 50% of the account balance per violation, whichever is greater, plus potential criminal penalties up to $250,000 and five years in prison for willful noncompliance. Even non-willful violations trigger penalties of $16,536 per report in 2025.

Your professional reputation suffers when clients discover you’ve cost them tens of thousands in unnecessary taxes or exposed them to IRS scrutiny. They lose trust in your entire practice. Referrals dry up, and your firm’s credibility erodes in the high-net-worth market you’ve worked hard to cultivate.

Your Path to Becoming the Cross-Border Expert Your Clients Trust

Optimise Accountants partners with US financial advisors like you to ensure seamless coordination between the US and UK tax regimes. We don’t replace you in your client relationships. Instead, we work behind the scenes as your specialised support team, giving you the knowledge and documentation you need to lead with confidence.

Led by Simon Misiewicz, FCCA, ATT, EA, MBA, a dual-qualified UK Chartered Certified Accountant and IRS Enrolled Agent, our team helps you align filings, minimise tax exposure, and preserve client trust through specialist treaty-driven compliance. Simon’s unique combination of credentials, including Certified Acceptance Agent status and IRS-Approved CE/CPD Educator designation, means he understands both HMRC and IRS systems at the deepest level.

Simon understands what you’re experiencing. “US advisors face pressure to serve British clients but lack UK-specific training,” he explains. “You shouldn’t have to choose between serving these clients and managing overwhelming compliance risk. That’s where partnership creates value.”

What’s at Stake: The Cost of Delay vs. the Value of Action

Understanding what you stand to gain or lose makes this decision clearer.

If you delay or refer clients away If you partner with Optimise today
Missed PFIC, FATCA, or pension reporting leading to six-figure penalties Coordinated disclosures preventing double taxation and penalty exposure
Overstated US income when UK pensions weren’t properly analysed under treaty provisions Accurate treaty relief under Articles 17 and 24, reducing your client’s effective tax rate by 22% or more
UK inheritance tax exposure for long-term US residents with British assets Pre-emptive estate planning across both systems, protecting generational wealth
Lost high-value clients who need specialised advice Professional credibility and strengthened client retention in the affluent market
Referring valuable relationships to competitors Building a reputation as the go-to advisor for British expatriates and investors

Our Partnership Services: Clear Packages for Every Client Need

We’ve structured our services to match exactly where you and your clients are in the cross-border compliance journey:

Service Tier Ideal For Description Key Deliverables Typical Outcome
Essential Advisory Support Advisors needing targeted, one-off guidance on a client’s UK/US tax matter Designed for ad-hoc consultation or initial client assessment. Provides expert clarification on UK tax provisions, treaty issues, or filing obligations. • Single consultation• Written summary of findings• Recommended next steps Immediate clarity on cross-border treatment and whether the British client fits your practice
Partnership Program Advisors with recurring British clients needing ongoing UK tax collaboration Ongoing technical partnership — Optimise acts as your UK tax back-office, ensuring consistent, compliant, and coordinated advice throughout the year. • Quarterly coordination• Annual filing support• Treaty optimisation• Priority technical access Seamless integration of UK expertise into your client service, ensuring consistent compliance and peace of mind
Complex Case Resolution Advisors whose clients have multi-year gaps, PFIC exposure, or backdated compliance issues Specialist service for high-risk cases requiring multi-jurisdictional expertise and direct HMRC/IRS coordination. • Preparation of historical returns• Streamlined filing procedures• Negotiation with HMRC/IRS Restored compliance status and protection from penalties — saving clients up to $300,000+
Client Protection Strategy Call All advisory partners Discovery call to determine the right support level based on client complexity and practice goals. • 30-minute strategy call• Custom service recommendation Identifies the most effective partnership model for your advisory firm

Essential Advisory Support: For advisors who need guidance on a specific client situation or one-time compliance question. Perfect when you’re evaluating whether a new British client fits your practice or need clarity on a particular UK tax provision. Single consultation with written summary of findings and recommended actions.

Partnership Program for advisors regularly serving British clients who need reliable, ongoing support. We become your behind-the-scenes technical team for UK tax matters, providing quarterly coordination, annual filing support, and treaty optimisation. Most advisory firms choose this option for peace of mind and consistent client service quality.

Complex Case Resolution For advisors whose clients face backdated compliance issues, significant PFIC exposure, or multi-year filing gaps. We prepare historical returns, coordinate streamlined filing procedures, and negotiate with HMRC or IRS when needed. This service has saved clients over $300,000 in potential penalties and restored full compliance status.

Schedule Your Client Protection Strategy Call to discuss which package aligns with your practice needs and client complexity.

Real Stories: How Advisors Transform Their Practice Through Partnership

From Referring Away to Retaining High-Value Clients

James, a Florida-based RIA, faced a difficult decision three years ago. Several of his retirement-age clients had UK pensions, and he lacked confidence advising them on cross-border tax implications. “I was sending valuable, long-term clients to other advisors because I didn’t know how to handle the UK side,” he admits. “It felt like admitting failure every time.”

After partnering with Optimise, James’s practice transformed. His British retirees were drawing UK pensions without proper Article 17 applications, resulting in effective tax rates 22% higher than necessary. Optimise restructured the filings, claimed appropriate foreign tax credits, and restored full compliance across eight client accounts.

“Now, when a prospective client mentions British origins or a UK pension, I’m excited rather than worried,” James says. “Optimise handles the technical complexity, and I present the strategies to my clients. They see me as the expert who can serve their full financial picture, and my retention rate with these clients is 100%.”

From Uncertain to Confident in Cross-Border Advice

Michael, a California-based EA, inherited a client with £750,000 in UK ISAs. “I knew there was something called PFIC exposure, but I’d never actually prepared Form 8621,” he explains. “The client was facing potential IRS penalties, and I was in over my head.”

Optimise prepared six years of backdated Form 8621s, secured streamlined filing compliance, and prevented $300,000 in potential IRS penalties. They also educated Michael on PFIC rules and provided templates for future filings.

“The relief was immediate,” Michael says. “Not just for my client, but for me professionally. I learned how to spot PFIC issues early and counsel clients properly. Last month, I confidently advised a new British client to restructure their investments before PFIC problems developed. That would have been impossible a year ago.”

From Overwhelmed to Supported

Jennifer, a wealth manager in Texas, serves multiple British families with complex cross-border estates. “Every tax season felt like chaos,” she describes. “UK tax years don’t align with US calendar years, pension taxation rules seemed contradictory, and I was constantly worried I’d missed something critical.”

After implementing quarterly reviews with Optimise, Jennifer’s practice runs smoothly. “They prepare reconciliations each April and December to align income recognition across both jurisdictions,” she explains. “My clients receive proactive planning rather than reactive crisis management. One client recently told me, ‘You’re the only advisor I’ve met who truly understands both systems.’ That referral became three new British client families.”

Understanding the Five Common Tax Traps Facing Your British Clients

You’ve probably encountered these situations with your British clients, feeling the frustration when traditional US tax strategies don’t apply cleanly. Here’s what your clients face and how partnership helps you address each challenge:

UK Pension Double-Taxation Exposure The scenario is familiar: your client receives their 25% UK pension lump sum, tax-free under UK rules, and assumes it’s tax-free everywhere. Then tax season arrives, and you discover the IRS treats it as fully taxable income unless specific treaty provisions are properly applied. Your client feels blindsided, and you’re left explaining a surprising five-figure tax bill. Through proper Article 17 treaty application and strategic timing, you can legitimately reduce or eliminate this tax exposure, but only if the paperwork is filed correctly and proactively.

PFIC Nightmare via ISAs: Most UK funds held in ISAs trigger Form 8621 reporting requirements and can create effective US tax rates exceeding 50% on gains. Your British clients invested in these vehicles following UK financial advice, never imagining they’d create US tax complications. When you discover the PFIC issue, you face the uncomfortable task of explaining that their “tax-efficient” UK investment is actually a US tax disaster. The right approach involves early identification, proper annual reporting, and, if necessary, restructuring into US-domiciled ETFs or direct equities to avoid PFIC classification entirely.

Dual Inheritance Tax Exposure Without proactive planning, UK-domiciled clients may face estate tax in both jurisdictions. The UK’s new residence-based inheritance tax rules (effective April 2025) determine liability based on 10 years of residence in the previous 20 tax years, regardless of traditional domicile status. Your clients of British origin who’ve lived in the US for extended periods face complex exposure that requires careful treaty analysis and preemptive trust structuring.

Timing Mismatches Creating Double Inclusion Risk The UK tax year runs from April 6 to April 5, while the US uses the calendar year. This fundamental mismatch leads to income recognition disputes when not properly coordinated. You’ve likely encountered situations where the same income appears to be taxable in both years or gets missed entirely, depending on which country’s rules you follow. Proper reconciliation each April and December prevents these mismatches, but requires understanding both systems simultaneously.

Recent Regulatory Changes Affecting Your British Clients in 2025

Staying current with both HMRC and IRS guidance protects your clients and your practice. Here are the most important updates for 2025:

The Foreign Earned Income Exclusion increased to $130,000 for 2025, up from $126,500 in 2024, according to Revenue Procedure 2025-32. This inflation adjustment affects the amount of foreign-earned income your British clients can exclude when calculating their US tax liability.

With approximately 900,000 US expats filing returns annually and over 1 million FBAR submissions each year, the IRS continues to aggressively enforce foreign account reporting requirements. Non-filing of Form 8938 (FATCA) can lead to fines of $10,000 to $50,000 if the failure continues after an IRS notice.

The Finance Act 2025 abolished the UK remittance basis for non-domiciled individuals effective April 6, 2025. Tax status is now determined by residence, not domicile, fundamentally changing how your British clients’ foreign income is taxed in the UK. A new four-year Foreign Income and Gains (FIG) regime provides 100% exemption from UK tax on foreign income and gains for individuals who haven’t been UK tax resident for at least 10 consecutive years prior to arrival, but this only applies to the first four years of UK residence.

UK inheritance tax exposure shifted from domicile-based to residence-based testing. Individuals are now liable to IHT on worldwide assets if they have been resident in the UK for at least 10 of the previous 20 tax years, regardless of their domicile status.

Area 2025 Update Source / Authority Key Implications for Advisors
Foreign Earned Income Exclusion (FEIE) Increased to $130,000 for 2025 (up from $126,500 in 2024). IRS Revenue Procedure 2025-32 Review client eligibility for FEIE and housing exclusion. Adjust projections for US clients working abroad.
FATCA & FBAR Enforcement Around 900,000 US expats file returns annually and 1 million+ FBARs are submitted. IRS continues strict enforcement. IRS Publication 5569; FATCA/FBAR compliance data Ensure clients file Form 8938 (FATCA) and FinCEN 114 (FBAR). Non-filing penalties range from $10,000–$50,000.
UK Remittance Basis Abolished The Finance Act 2025 ended the remittance basis from 6 April 2025. Taxation now based on residence, not domicile. Finance Act 2025 (UK) Reassess all non-dom clients. Foreign income and gains are taxable if resident, unless qualifying under FIG regime.
New Foreign Income & Gains (FIG) Regime 100% UK tax exemption on foreign income/gains for first 4 years of UK residence, if not UK-resident for previous 10 consecutive years. HMRC Policy Paper: Foreign Income and Gains Regime 2025 Identify eligible arrivals. Plan timing of asset disposals and income recognition within the 4-year window.
Inheritance Tax (IHT) Residence Rule IHT now applies to worldwide assets after 10 of the previous 20 tax years of UK residence — domicile no longer decisive. HMRC Inheritance Tax Manual (IHTM13000 update, 2025) Review clients’ long-term residence. Consider trusts, life insurance, and emigration timing for IHT exposure mitigation.

Practical Solutions: How to Address Each Challenge

We Understand Your Challenge

As a US advisor, you feel the pressure to serve British clients who need your guidance, but you didn’t receive UK-specific training in your professional education. Your EA or CPA credentials have thoroughly prepared you for US taxation, but HMRC regulations, UK treaty provisions, and cross-border timing issues remain foreign territory.

You’ve probably experienced that sinking feeling when a prospective client mentions UK pensions or investments. You know you should serve them confidently, but you’re unsure whether you understand all the implications. Perhaps you’ve spent hours researching UK tax rules, only to remain unsure whether your interpretation is correct. Maybe you’ve already referred valuable clients elsewhere, watching other advisors build the cross-border speciality you wish you had.

This pressure creates a difficult position. High-net-worth British clients need sophisticated advice, and your competitors may be serving them confidently (or at least appearing to). You risk losing market share in this affluent segment, damaging your practice’s growth potential and professional reputation.

Why Advisors Trust Optimise Accountants

Simon Misiewicz brings credentials that bridge both tax systems completely. As a Fellow of the Association of Chartered Certified Accountants (FCCA), a member of the Association of Taxation Technicians (ATT), and an IRS Enrolled Agent (EA), he holds the highest professional designations in both UK and US taxation. His MBA, Certified Acceptance Agent status, and IRS-Approved CE/CPD Educator certification demonstrate depth that few practitioners can match.

Optimise has helped advisors successfully navigate complex situations for over a decade. Our client retention rate exceeds 95%, and we’ve prepared hundreds of dual-jurisdiction filings without a single successful IRS or HMRC challenge to our positions.

“I’ve worked with several tax advisors over the years, but Simon’s dual qualification made an immediate difference,” shares Robert Chen, a Connecticut-based financial planner. “He doesn’t just understand both systems; he understands how they interact. That distinction saved my client £45,000 in the first year alone.”

Maria Gonzales, managing partner at a Boston RIA, adds: “Before partnering with Optimise, we turned away British clients because the liability risk seemed too high. Now we actively market to this demographic. Simon’s team provides the technical foundation, we deliver the client service, and everyone wins.”

Your Questions Answered

Do British clients in the US need to file UK returns? Only if they continue earning UK income, such as rental income or pensions. HMRC requires a declaration even for non-residents with UK-sourced income. Many British clients believe leaving the UK ends their UK filing obligations, but source-based income remains reportable. We help you determine exactly what your client must file and what they can safely omit.

Are UK ISAs recognised by the IRS? No. Despite their tax-advantaged status in the UK, the IRS treats ISAs as regular investment accounts. Any income or gains are fully taxable to US taxpayers and typically trigger PFIC filing requirements that create additional complexity and potential penalties.

Can the US-UK treaty prevent double taxation? Yes, through Article 24, foreign tax credits and Article 17 pension provisions. However, automatic relief doesn’t happen. You must make proper elections and file the appropriate forms to claim treaty benefits. Without these filings, your client pays tax to both countries despite treaty protections designed to prevent exactly that outcome.

How can US advisors ensure accurate reporting? Partner with dual-qualified professionals who understand both HMRC and IRS systems. Attempting to self-educate on UK taxation takes hundreds of hours and still leaves gaps in practical application. Our partnership model gives you immediate access to this expertise without the investment of becoming a UK specialist yourself.

What’s the best starting point? Book a joint consultation with Optimise to map compliance duties on both sides. In one conversation, you’ll gain clarity on what’s required, what risks exist, and how to present a comprehensive solution your client will trust. There’s no obligation, and many advisors find the consultation alone provides immediate value.

Start Building Your Cross-Border Expertise Today

You have three ways to begin transforming how you serve British clients:

Schedule Your Client Protection Strategy Call. Discover how to safeguard your British clients from double taxation, penalty exposure, and compliance failures. In this consultation, we’ll review a specific client situation (keeping details confidential) and show you exactly how the partnership would work in practice.

Don’t let another valuable British client walk away because you lacked specialised UK support. Your competitors are building cross-border capabilities, and the window to establish yourself as the trusted advisor for British expatriates and investors is narrowing.

About Simon Misiewicz FCCA ATT EA MBA

Simon Misiewicz is the Founder and Director of Optimise Accountants Limited, a dual-qualified UK-US tax advisory firm specialising in cross-border planning for individuals, families, and professional advisors.

As a Chartered Certified Accountant (FCCA), Chartered Tax Adviser (ATT), IRS Enrolled Agent (EA), Certified Acceptance Agent (CAA), and IRS-Approved CE/CPD Educator, Simon uniquely bridges both UK and US tax systems. This combination of credentials, earned through rigorous examination and continuing education in both jurisdictions, positions him among fewer than 100 practitioners worldwide with full dual qualification.

Simon’s expertise covers US/UK tax treaty coordination (Articles 17 and 24) for pensions, investments, and income streams; PFIC and Form 8621 mitigation for ISAs, OEICs, and UK collective funds; cross-border pension planning ensuring withdrawals and lump sums are taxed correctly; inheritance and estate planning for dual residents, integrating UK IHT and US estate tax exposure; and advisor-to-advisor collaboration, supporting US CPAs, EAs, and UK wealth managers with dual-reporting clients.

Through Optimise Accountants and InternationalTaxesAdvice.com, Simon provides strategic, transparent, and data-driven solutions for Americans living in the UK and Britons investing or residing in the US, ensuring clients remain fully compliant while legally minimising global tax burdens.

“My mission is to make international taxation understandable and manageable,” Simon explains. “Americans and Britons shouldn’t fear compliance; they should use it to their advantage. US advisors shouldn’t have to choose between serving British clients and managing overwhelming risk. Partnership creates the best outcome for everyone.”

Simon regularly speaks at IRS-approved continuing education programs, teaching US tax professionals how to identify and address UK tax issues affecting their clients. His practical, no-nonsense approach has earned him the trust of advisory firms across the United States seeking to confidently serve the growing British expatriate and investor market.