Introduction: Expat Tax Seattle Planning Beyond the No-Income-Tax Headline
The expat tax Seattle question most British professionals ask before relocating is simple: how much will I keep now that Washington has no income tax? The honest answer is that your salary and bonus escape state tax, but your investment gains do not. Washington charges a capital gains tax of 7%, rising to 9.9% on the largest gains. Furthermore, voters decide in November 2026 whether a new 9.9% income tax on household income above $1 million survives to 2028.
At TaxYork, we prepare returns for British engineers, executives, founders and investors who move to Seattle, Bellevue, Redmond and Kirkland. In our experience, most of them arrive with a UK share portfolio, ISAs, a workplace pension and a London flat. Consequently, the expat tax Seattle position is rarely about wages alone. Instead, it turns on what you sell, when you sell it, and whether you have already become domiciled in Washington.
Expat Tax Seattle Basics: Three Layers of Tax, Not One
Every British resident of Seattle deals with three layers. First, federal income tax reaches your worldwide income at rates up to 37%, plus the 3.8% net investment income tax. Second, Washington taxes long-term capital gains and funds itself through sales, property and payroll-based levies. Third, the United Kingdom keeps taxing UK rental income and can reach gains if you return too soon. Therefore sound expat tax Seattle compliance means managing all three together rather than one at a time.
Who This Guide Is Written For
This guide addresses high-net-worth British nationals, dual national US UK families and accidental Americans living in the Seattle area. Specifically, it suits technology executives on L-1 or H-1B visas, green card holders, founders with equity and investors holding substantial UK portfolios. If your household income runs into six or seven figures, every expat tax Seattle rule below carries a real price tag. For the national picture, read our complete guide to UK expat tax in the USA.
What Washington Does and Does Not Tax in 2026
Washington has no personal income tax on wages, interest or dividends in 2026. However, the state is not tax-free, and the gaps catch newcomers every year. Understanding each charge gives you the full expat tax Seattle picture before you model your federal return.
The Capital Gains Excise Tax: 7% and 9.9%
The Washington capital gains tax applies to long-term gains from selling stocks, bonds, fund units and business interests. Moreover, the Department of Revenue's notice on the new tiered rates confirms that from the 2025 tax year the first $1 million of taxable gains bears 7%. Any taxable gain above $1 million bears an extra 2.9%, so the top marginal rate is 9.9%. The standard deduction was $278,000 for 2025, and it rises with inflation each year.
Notably, the tax follows your federal net long-term capital gain. Short-term gains on assets held for a year or less are not taxed by the state at all. In addition, the state treats the charge as an excise on the sale of assets rather than an income tax, which is how it survived its constitutional challenge. For expat tax Seattle purposes, this means your UK shares, ETFs and investment trusts all fall inside the base once you sell them at a long-term gain.
What the Capital Gains Tax Exempts
Several important assets sit outside the state charge. Specifically, the Department of Revenue exempts real estate and interests in real estate, assets held in certain US retirement accounts, timber, livestock used in farming and depreciable business assets. As a result, selling your London flat or your Seattle home creates no Washington capital gains tax at all. Similarly, gains excluded from federal income under section 1202 stay outside the Washington base.
However, that section 1202 exclusion only helps shareholders in a domestic US C corporation. Consequently, a British founder selling shares in a UK limited company can never use it, however long the holding period. We see this misunderstanding regularly in expat tax Seattle engagements involving earlier UK start-ups.
Sales Tax, Property Tax and the Real Estate Excise Tax
Washington relies heavily on consumption taxes, and Seattle's combined sales tax rate now exceeds 10%. Additionally, when you sell Washington property, the seller normally pays the real estate excise tax. The state portion is graduated: 1.1% up to $525,000, 1.28% to $1,525,000, 2.75% to $3,025,000 and 3% above that. Therefore a $4 million Medina or Laurelhurst home sale carries a meaningful transaction charge, even though no capital gains tax applies.
Payroll Levies: Paid Leave and WA Cares
Wages escape income tax, but two payroll premiums still apply. First, the Paid Family and Medical Leave premium rose to 1.13% for 2026, according to the Employment Security Department, on wages up to the $184,500 Social Security cap, with employees bearing most of it. Second, the WA Cares long-term care premium takes 0.58% of wages with no cap.
Importantly, the WA Cares exemption rules changed on 1 January 2026. Employees on temporary non-immigrant work visas, such as L-1 and H-1B holders, are now automatically exempt unless they choose to participate. However, the exemption ends when you receive a green card. Hence a British executive earning $900,000 who converts to permanent residence starts paying roughly $5,220 a year in WA Cares premiums. Our guide to H-1B visa tax for British professionals covers the federal side of that visa.
The 2028 Washington Income Tax and the November 2026 Vote
The most significant expat tax Seattle development of 2026 is not a capital gains change at all. Instead, it is the state's first broad personal income tax, which may never take effect.
What ESSB 6346 Does
Governor Ferguson signed ESSB 6346 on 30 March 2026. The law imposes 9.9% on Washington taxable income above a $1 million standard deduction, starting on 1 January 2028. Crucially, married couples and registered domestic partners share a single $1 million deduction rather than doubling it. The starting point is federal adjusted gross income, so wages, bonuses, vested RSUs, pass-through business income and investment income all count. Furthermore, a non-refundable credit for Washington capital gains tax paid in the same year prevents the same long-term gain being taxed twice. The first annual returns fall due in April 2029.
Initiative 645 and the Constitutional Challenge
Opponents gathered more than 511,000 signatures, and Initiative 645 was certified for the 3 November 2026 ballot, as Ballotpedia reported. If approved, it repeals the 9.9% income tax before its effective date and restores a general ban on individual income taxes. Meanwhile, a separate constitutional lawsuit continues in the Klickitat County Superior Court. Therefore nobody can yet say whether the tax will ever be collected.
Expat Tax Seattle Planning Around an Uncertain Tax
For a British household earning $1.4 million, the tax would cost about $39,600 a year from 2028 if it survives. Consequently, sensible expat tax Seattle planning keeps options open rather than betting on the vote. In particular, clients with discretion over bonus timing, deferred compensation or the exercise of options should model 2027 and 2028 separately. Alternatively, a planned return to London in 2028 may remove the exposure entirely, because part-year residents receive a proportionate deduction adjustment.
Federal Deductions: The SALT Cap and Washington Sales Tax
Because Washington levies no income tax, residents who itemise may deduct state and local sales tax instead of income tax on their federal return. Additionally, the One Big Beautiful Bill Act raised the cap on state and local tax deductions to $40,000 for 2025 and $40,400 for 2026. However, the higher cap shrinks by 30% of modified adjusted gross income above $500,000, or $505,000 for 2026, and never falls below $10,000. Consequently, most high-earning expat tax Seattle clients are back at the $10,000 floor. In practice, property tax on a Seattle home usually uses that allowance up on its own, so sales tax records rarely change the federal result for wealthy households.
How You Become Taxable in the US and in Washington
Federal residence and Washington domicile use different tests. Moreover, the UK applies its own statutory residence test on the way out. Getting the dates right is the foundation of every expat tax Seattle return we prepare.
Federal Residence: Green Card and Substantial Presence
You become a US tax resident by holding a green card or by meeting the IRS substantial presence test. That test counts all days in the current year, one third of last year's days and one sixth of the year before, and it is met at 183 weighted days. As a result, most L-1 and H-1B transferees become resident in their first calendar year.
The arrival year is usually a dual-status year. You are a nonresident until your residency starting date and a resident afterwards. Additionally, you may qualify for a first-year choice election or a joint return election. Our guide to the dual-status tax year for US-UK movers explains each option, and IRS Publication 519 sets out the rules in full.
Washington Domicile and Why It Matters for Gains
Washington allocates gains from intangible assets, such as shares, to the state if you were domiciled there at the moment of sale. Domicile means your true, fixed and permanent home, which is a question of intent as well as presence. Consequently, a Briton who sells a UK portfolio in London before moving creates no Washington liability. By contrast, the same sale three months after arrival generally does.
However, visa status does not settle domicile on its own. The Department of Revenue looks at where you live, where your family is, where you vote, and where you intend to remain. Therefore expat tax Seattle clients should never assume that a temporary visa keeps them outside the state charge. Instead, document your facts and time large disposals deliberately.
Leaving the UK Under the Statutory Residence Test
On the UK side, the statutory residence test guidance decides when your UK residence ends. Most relocating employees qualify for split-year treatment under the full-time work overseas case, and an accompanying partner can use the partner case. Consequently, UK tax on foreign income usually stops from the date of departure. Nevertheless, you still file a Self Assessment return for the departure year, and missed UK tax returns for that year are one of the most common problems we correct.
Dual Nationals and Accidental Americans Moving to Seattle
Not every British arrival is new to the IRS. Some clients hold US citizenship through a parent, and others acquired it by birth during a brief US posting decades ago. These accidental Americans and dual national US UK clients were taxable in the United States throughout their London years, whether or not they ever filed. Consequently, moving to Seattle often exposes years of missed US tax returns and missed FBARs at exactly the moment a new employer runs background and payroll checks. Therefore the expat tax Seattle review for a dual national starts with the historic position, not the move. Where earlier years were missed without wilful intent, a structured offshore disclosure resolves them before any sale of UK assets makes the gap larger.
Selling Your UK Portfolio: Before or After You Land
Timing a portfolio sale around the move is the single most valuable expat tax Seattle decision a British investor makes. Moreover, it is the decision most relocation guides ignore completely.
Selling While Still UK Resident
If you sell before your US residency starting date, the United States generally has no claim on a foreign-source gain realised by a nonresident alien. Similarly, Washington has no claim, because you are not yet domiciled there. Instead, UK capital gains tax applies at the current rates of 18% and 24%, after a £3,000 annual exempt amount. For a higher-rate taxpayer, the effective charge is therefore close to 24%.
Selling After You Arrive
Once you are a US resident and domiciled in Washington, the same gain faces 20% federal tax, the 3.8% net investment income tax and 7% or 9.9% state tax. For expat tax Seattle purposes, that totals 30.8% or more. Furthermore, the United States gives you no basis step-up on arrival. Consequently, every pound of growth accrued during your London years becomes US-taxable and Washington-taxable when you finally sell.
Currency makes this worse. The IRS measures your gain in dollars, using the exchange rate on the purchase date and the sale date. Therefore a sterling holding that barely moved in pounds can still show a large dollar gain if sterling strengthened. In practice, expat tax Seattle projections must be run in both currencies before you decide.
UK Funds, ISAs and the Washington Base
UK ISAs lose their tax-free status the moment you become a US resident. Consequently, dividends, interest and gains inside them are reportable on your Form 1040, and long-term gains flow into the Washington calculation. In addition, most UK collective funds and ETFs are passive foreign investment companies for US purposes. Excess distribution gains on those funds are taxed federally as ordinary income with an interest charge, so they generally sit outside the Washington capital gains base. Nevertheless, in expat tax Seattle cases the federal cost usually far exceeds any state saving, so restructuring before arrival remains the better route.
Temporary Non-Residence: The Five-Year Trap
Many expat tax Seattle clients plan to return to London within a few years. However, the UK's temporary non-residence rules can pull gains back into charge. If you were UK resident in at least four of the seven years before leaving and return within five years, gains on assets you owned before departure become taxable in the UK in the year you come back. Our guide to temporary non-residence for internationally mobile families explains the mechanics.
In that situation, the same gain could suffer federal tax, Washington tax and UK tax. Fortunately, Washington allows a credit for income or excise tax paid to another taxing jurisdiction, and that definition expressly includes foreign countries. Moreover, the Department of Revenue's interim statement on the credit presumes that an intangible asset is located in the jurisdiction that legally taxed its gain. Therefore a well-prepared expat tax Seattle file preserves every record needed to claim that credit later.
Equity Compensation, Property and Pensions
Seattle's economy runs on equity-heavy pay packages. Consequently, RSUs, options and property questions dominate most expat tax Seattle returns we prepare for British households in the region.
RSUs and Stock Options
RSUs are taxed as wages when they vest, so Washington charges no state income tax on the vesting value. However, if you hold the vested shares for more than a year and sell at a gain, that gain enters the Washington capital gains base. Additionally, RSUs granted in London and vesting in Seattle create a split: HMRC taxes the portion earned during UK workdays, while the IRS taxes the full amount as a resident. Our guide to cross-border RSU tax on UK vesting covers the foreign tax credit that resolves the overlap.
Your London Home and UK Rental Property
Under expat tax Seattle rules, selling your former UK home creates no Washington tax, because real estate is exempt. Nevertheless, the federal return still reports the gain, and the section 121 exclusion of up to $500,000 for joint filers only applies if you owned and lived in the property for two of the previous five years. Furthermore, the UK requires a non-resident capital gains tax return within 60 days of completion, even where private residence relief removes the tax.
If you let the flat instead, the UK taxes the rental profit and your agent withholds basic-rate tax unless HMRC approves gross payment. Notably, the UK property income rates rise to 22%, 42% and 47% from 6 April 2027, and the withholding rate follows. Our guide to stopping 20% non-resident landlord withholding explains the approval process, and the gov.uk guidance on UK income while living abroad confirms your filing duties.
UK Pensions Under the Treaty
The US-UK double taxation convention generally lets a UK pension grow without current US tax while you live in Seattle. However, lump sums need careful modelling, because the treaty's savings clause and US reporting rules can remove the expected exemption. Moreover, Washington's retirement account exemption refers to US-qualified plans, so do not assume it extends automatically to a SIPP. Our cross-border planning service models drawdown timing before you touch a UK pension.
Missed FBAR and Form 8938 Reporting After the Move
Reporting failures cause more expensive expat tax Seattle problems than any rate. Most British arrivals simply do not know that UK accounts they have held for decades are now reportable.
Who Must Report and What Counts
Every US tax resident, including green card holders and visa holders meeting the substantial presence test, must file an FBAR with FinCEN when foreign accounts together exceed $10,000 at any point in the year. Current accounts, savings accounts, ISAs, brokerage accounts and many pension arrangements all count for expat tax Seattle reporting purposes. The FinCEN FBAR filing page sets the April deadline with an automatic extension to October.
Separately, Form 8938 applies to residents once specified foreign assets exceed $50,000 at year end or $75,000 at any time for single filers. Joint filers living in the United States use $100,000 and $150,000. The IRS comparison of Form 8938 and FBAR requirements shows how the two overlap. Our FBAR and FATCA reporting service prepares both.
Penalties and Putting Missed Reporting Right
Non-wilful FBAR penalties reach $16,536 per report in 2026, while wilful penalties reach the greater of $165,353 or 50% of the balance. Moreover, the IRS withdrew its Delinquent FBAR Submission Procedures on 1 July 2026. Consequently, late filers now need a properly documented reasonable cause position, or a formal offshore disclosure route where income was also omitted. Therefore any expat tax Seattle client who has missed a year should correct it before the IRS writes first.
Missed Reporting on Pensions, ISAs and Investment Accounts
The accounts most often left off are the ones clients do not think of as bank accounts. Specifically, stocks and shares ISAs, general investment accounts, Premium Bonds holdings and workplace or personal pensions all require analysis for FBAR and Form 8938 purposes. Moreover, ISA income is taxable on the Form 1040 itself, so missed reporting usually means an understated return as well as a missing form. In our experience, the typical Seattle arrival has between six and twelve reportable UK accounts. As a result, an expat tax Seattle catch-up project should inventory every UK relationship first, then decide which years need amended returns and which need only late information filings.
A Worked Case Study: The Bellevue Couple Who Overpaid $19,460
The following illustrative case study reflects the kind of expat tax Seattle engagement we handle regularly. Names and details are changed.
The Facts
James and Sophie moved from London to Bellevue in August 2024, when James took a senior engineering leadership role on an L-1A visa. Both are British citizens, and they filed a joint US return for 2025. James earned $720,000 in salary and vested RSUs. In June 2025 they sold a UK share portfolio held directly for many years, receiving $2,400,000 against a dollar cost basis of $1,250,000. Therefore their long-term gain was $1,150,000, of which about $700,000 had accrued before they left London.
Additionally, they held £180,000 across two stocks and shares ISAs, a UK current account and a workplace pension. Nobody had told them about FBARs, so their 2024 FBAR was never filed. Furthermore, their 2024 return omitted $6,200 of ISA dividends.
What the Sale Cost
Because their ordinary income already exceeded the 20% threshold, the whole gain bore 20% federal tax, or $230,000. In addition, the net investment income tax added $43,700. Washington then taxed the gain above the $278,000 deduction: $872,000 at 7%, which is $61,040. Consequently, the single sale cost $334,740 in federal and state tax, an effective rate of 29.1%.
What Planning Would Have Saved
Had they split the sale evenly across June 2025 and January 2026, each year's $575,000 gain would have used a separate Washington standard deduction. The 2025 half would have borne ($575,000 − $278,000) × 7%, or $20,790. The 2026 deduction is indexed upwards, so the 2026 half would have cost no more than $20,790. As a result, the Washington tax would have fallen to at most $41,580, saving at least $19,460 with no increase in federal tax.
Better still, selling the pre-arrival portion before August 2024 would have kept it out of both the US and Washington bases entirely. Instead, that $700,000 of London growth would have faced UK capital gains tax at up to 24% while they were still UK resident, rather than a combined 30.8% after arrival.
What We Fixed
We filed their late 2024 FBAR with a detailed reasonable cause statement and prepared a Form 1040-X reporting the omitted ISA dividends. Furthermore, we added Form 8938 for 2024 and 2025, and we reviewed their UK departure-year Self Assessment return, which had wrongly claimed full-year non-residence instead of split-year treatment. Finally, we mapped their remaining UK holdings against the temporary non-residence window, because they plan to return to London in 2028. Thus the family ended with compliant reporting and a clear expat tax Seattle plan for every future disposal.
How TaxYork Can Help With Expat Tax Seattle Compliance
TaxYork provides comprehensive US tax return preparation for British families and dual national US UK households in Seattle and across Washington. We prepare dual-status and joint Forms 1040, calculate Washington capital gains tax returns and handle every FBAR and Form 8938 filing. Additionally, we coordinate your UK Self Assessment, split-year claims, non-resident landlord filings and non-resident capital gains returns so both systems agree.
Furthermore, where earlier years contain missed returns or missed reporting on pensions, ISAs or investment accounts, we prepare the corrective filings and offshore disclosure in full. Where treaty positions matter, our tax treaty optimisation service secures the credits you are due. Therefore you deal with one team for every expat tax Seattle obligation on both sides of the Atlantic. If you are weighing Seattle against other destinations, compare our guides to expat tax in San Francisco and expat tax in Texas.
Conclusion
Seattle offers British professionals a genuine advantage: no state tax on salary, bonuses or vesting RSUs. However, Washington's 7% and 9.9% capital gains tax reaches the UK portfolios that high earners bring with them, and the 2028 income tax may yet add a second layer. Moreover, federal tax, UK residence rules and foreign account reporting all continue to apply, so expat tax Seattle compliance is never a single-form exercise. Ultimately, the families who benefit most are those who time their disposals, document their domicile and correct any missed reporting before the first Washington return is due. To see how different investment choices affect your position, try our US-UK tax calculators.
Contact Us
If you are moving to Seattle or already living there, the right expat tax Seattle preparation now avoids costly corrections later. Please book a consultation with our US-UK tax specialists to review your position. You can also email hello@taxyork.com or call 020 3488 8606. Alternatively, visit TaxYork to explore our full range of cross-border services.
Disclaimer
This article provides general information about expat tax Seattle rules and does not constitute tax or legal advice. Tax law changes frequently, and Washington's income tax remains subject to a November 2026 ballot and pending litigation. Furthermore, the figures cited reflect published guidance at the date of writing, and the case study is illustrative. Readers should also review IRS Topic 409 on capital gains and losses and material from the Chartered Institute of Taxation and the ICAEW. Therefore always obtain professional guidance tailored to your own position before acting.