Guide to U.K-U.S. Cross-Border Tax Planning

U.K.-U.S. tax planning involves understanding how income, residency and asset ownership are taxed under both British and American law. Dual residents, expatriates and cross-border investors often face parallel filing obligations, with each country maintaining its own system for taxing worldwide income. While a bilateral tax treaty exists to help reduce the chance of double taxation, U.S. citizens and green card holders living in the U.K. still must comply with IRS reporting requirements.

U.K.-U.S. tax planning affects a broad range of individuals and families, particularly U.S. citizens residing in the U.K., British nationals with U.S. investments and dual citizens.

American citizens living abroad are subject to U.S. taxation on their global income regardless of where they reside, which can create overlapping obligations with His Majesty’s Revenue and Customs (HMRC). Similarly, British residents who own U.S. property or work for U.S.-based companies may owe U.S. tax on income tied to those assets or activities.

For instance, an American living in London who earns income from a U.K. employer must file a U.K. tax return. They must also report that same income on their U.S. tax return, potentially triggering foreign tax credits or exclusions. Likewise, a British citizen receiving dividends from a U.S. corporation may be subject to U.S. withholding tax and must report that income to HMRC. Without coordinated planning, it’s possible to overpay—or underreport—resulting in audits or penalties on either side of the Atlantic.

The U.K.-U.S. Income Tax Treaty, first signed in 2001 and supplemented by subsequent protocols, outlines how income is taxed when a taxpayer has ties to both countries. It allocates taxing rights over specific types of income and helps reduce or eliminate double taxation through provisions like foreign tax credits, exemptions and mutual agreement procedures.

The treaty specifies which country has primary taxing rights over employment income, business profits, dividends, interest and pensions. For example, salaries are generally taxed only in the country where the work is performed, unless the income is below a certain threshold and the worker is present for fewer than 183 days in the tax year. U.S. citizens, however, do not receive full treaty benefits if they are taxed on worldwide income by the IRS, although they can still access credits and exclusions.

The treaty also includes tiebreaker rules to determine tax residency when someone qualifies as a resident in both countries under their respective domestic laws. These rules look at factors such as the location of a permanent home, the country of closest personal and economic ties and habitual abode. If none of these factors are conclusive, nationality may determine the outcome, or tax authorities in both countries may resolve the case through mutual agreement.

Understanding how income is taxed across both the U.S. and U.K. is key to effective cross-border planning. Tax treatment depends on the type of income and whether treaty provisions modify or override domestic rules in either country.

Employment income is typically taxed in the country where work is physically performed. A U.K. resident working remotely for a U.S. employer will generally owe U.K. tax on that income but must also report it to the U.S. if they’re an American citizen or green card holder. Self-employment income follows similar principles but may also be subject to additional reporting obligations under the Foreign Account Tax Compliance Act (FATCA).

U.K. pension income, such as distributions from self-invested personal pensions (SIPPs) or occupational pensions, is generally taxable only in the U.K. under the treaty. This is the case even if the recipient is a U.S. citizen. However, the IRS may still require reporting and potentially tax the income unless the taxpayer elects to defer taxation under Article 17 of the tax treaty.

Conversely, U.S. retirement accounts like IRAs and 401(k) plans may face tax in the U.S. when distributions occur. U.K. residents receiving these payments may also have to declare them to HMRC, depending on whether the treaty exempts the income or allows taxation in both jurisdictions. Contributions to retirement accounts often aren’t recognized for tax deferral across borders, leading to possible mismatches in timing and tax treatment.

Dividends from U.S. companies paid to U.K. residents are typically subject to a 15% U.S. withholding tax under the treaty. This is notably lower than the standard 30% rate for non-treaty countries. Interest income is often exempt from U.S. tax for U.K. residents. However, they must still report these payments to HMRC.

Capital gains are generally taxed only in the country of residence. A U.K. resident selling U.S. stock will pay U.K. capital gains tax, not U.S. tax. However, there are exceptions. Gains on U.S. real estate may be subject to both countries’ tax regimes, with the U.S. imposing tax under FIRPTA (Foreign Investment in Real Property Tax Act) rules.

Estate and inheritance taxation is an area of sharp divergence. The U.K. levies inheritance tax (IHT) on worldwide assets of individuals domiciled in the U.K. Meanwhile, the U.S. imposes estate tax on worldwide assets of its citizens and on U.S.-situated assets for nonresident aliens. The treaty provides limited relief by allowing a pro-rated unified credit and certain deductions.

For example, consider a U.S. citizen living in the U.K. who passes away with assets in both countries. They may face estate tax exposure on their global estate. The U.K. will also assess IHT on the entire estate if the deceased was considered U.K.-domiciled. Careful planning is required to coordinate the two systems and mitigate tax liability through exclusions, gifts and trusts.

U.K.-U.S. cross-border taxpayers often face complex and overlapping rules that can lead to unintended tax consequences. The following are some of the most common challenges that arise when navigating the two systems.

The U.K. tax year runs from April 6 to April 5, while the U.S. follows the calendar year. This discrepancy can complicate the timing of income recognition, foreign tax credit claims and reporting deadlines.

U.S. citizens and residents must file FBAR (FinCEN Form 114) if the aggregate value of foreign accounts exceeds $10,000 at any point in the year. FATCA also requires Form 8938 for specified foreign financial assets. Unlike FBAR, Form 8938 is filed with your income tax return and has higher reporting thresholds.

U.K. residents who claim non-domiciled status can use the remittance basis to limit U.K. taxation to U.K.-sourced income and foreign income brought into the U.K. However, U.S. citizens cannot benefit from this status for U.S. tax purposes. They must still report worldwide income.

U.S. taxpayers with U.K. pensions, individual savings account (ISA) or unit trusts may trigger PFIC rules. These rules impose harsh tax treatment and require special reporting (Form 8621). Even non-retirement savings accounts can cause compliance issues if they hold foreign mutual funds.

Cross-border tax obligations between the U.K. and U.S. often hinge on where income is earned, how it’s classified and what the taxpayer’s residency status is under each system. Filing requirements, treaty rules and differences in tax treatment across pensions, investments and estates can complicate compliance and financial decision-making. Those with ties to both countries frequently benefit from aligning their strategies with both domestic regulations and treaty provisions. A coordinated strategy that considers both domestic tax laws and treaty provisions can reduce inefficiencies, mitigate double taxation risk and simplify compliance.

• Consider working with a tax professional or a financial advisor with tax planning expertise. Finding a financial advisor doesn’t have to be hard. SmartAsset’s free tool matches you with vetted financial advisors who serve your area, and you can have a free introductory call with your advisor matches to decide which one you feel is right for you. If you’re ready to find an advisor who can help you achieve your financial goals, get started now.
• Roth conversions can trigger IRMAA surcharges on Medicare premiums if income crosses certain thresholds. Taxpayers nearing Medicare age should coordinate conversions to avoid unexpected premium increases. Spreading conversions over several years or timing them before age 63 can limit these surcharges.

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