Direct AnswerThe US and UK have both an income tax treaty and a Social Security totalization agreement, which together reduce double taxation and coordinate Social Security between the two countries. For British buyers, the key practical points are: US persons are taxed on worldwide income; UK ISAs are tax-free in the UK but generally not for US tax purposes; SIPPs and workplace pensions have treaty treatment but need careful handling; and foreign accounts can trigger FBAR and FATCA reporting. None of this is a substitute for a cross-border CPA. Brian is a REALTOR®, not a tax adviser - this page is general orientation.

The US-UK relationship is one of the most developed cross-border tax frameworks in the world - which is good news, but it doesn't make the details simple. Here's the orientation every British buyer should have before sitting down with a CPA.

Two agreements, not one

The US and UK have a comprehensive income tax treaty and a Social Security totalization agreement. The treaty allocates taxing rights and provides relief from double taxation; the totalization agreement helps you avoid paying Social Security/National Insurance into both systems at once and coordinates benefit credits.

Pensions and savings (general)

  • ISA - tax-free in the UK, but the IRS generally does not treat ISA income as tax-free; many US persons find ISAs lose their advantage and add reporting.
  • SIPP / workplace pensions - the treaty addresses pension treatment, and growth can often be deferred, but the analysis is technical - get it reviewed.
  • QROPS transfers carry their own US considerations.

Reporting: FBAR and FATCA

US persons (citizens, green-card holders, and many tax residents) must report worldwide income and may need to file an FBAR (FinCEN Form 114) for foreign accounts above the threshold, plus FATCA (Form 8938) in some cases. Penalties for missed foreign-account reporting are significant - this is exactly why a cross-border CPA matters.

Stamp Duty vs California: UK buyers pay Stamp Duty Land Tax on purchase. California has no equivalent statewide buyer tax; instead there's a documentary transfer tax (commonly seller-paid, varying by city/county) and annual property tax under Proposition 13. I'll show you the actual California closing-cost and carrying-cost picture for any property.

See also the UK relocation hub and the UK pension/SIPP guide.

Important - please read: Brian Cooper is a licensed California REALTOR® (DRE# 01434286), not an immigration attorney, CPA, tax adviser, or financial adviser. The visa, tax-treaty, FIRPTA, mortgage, and currency information here is general and educational - confirm your own situation with a qualified cross-border immigration attorney and CPA before acting. Any lender or service-provider referral is disclosed under RESPA. Equal Housing Opportunity - service-area awareness only, never steering by national origin or any protected class.
Primary sources: IRS - US Income Tax Treaties A to Z · SSA - US-UK Totalization Agreement · IRS - Report of Foreign Bank and Financial Accounts (FBAR) · IRS - FATCA