Introduction: What Tax Equalisation Really Costs a London Assignee
Tax equalisation promises that your London assignment will leave you no better and no worse off than staying in New York. Furthermore, the promise is usually kept. However, the mechanism that delivers it quietly rewrites almost every line of your Form 1040.
Senior assignees routinely misread this. Specifically, they assume their employer has taken the American filing problem away. In reality, the employer has taken the economic risk away and left the filing obligation exactly where it was. Consequently, the return becomes harder, not easier.
We prepare returns for managing directors, partners and senior executives moving between Wall Street and the City. Notably, the same three misunderstandings surface every year. Additionally, each one costs real money when the settlement lands.
Why Tax Equalisation Is Not an IRS or HMRC Programme
No tax equalisation election exists in the Internal Revenue Code. Similarly, HMRC operates no equalisation scheme. Instead, the arrangement is purely contractual, sitting between you and your employer.
Neither revenue authority recognises it, adjusts for it, or cares about it. Therefore, you still report worldwide income to the IRS. Moreover, you still file a Self Assessment return in Britain. The contract changes who bears the cost, never who bears the obligation.
That distinction matters enormously. For example, if your employer's provider files a late or wrong return, the penalty notice arrives addressed to you. Accordingly, you should read every return before it goes anywhere.
The Three Numbers That Drive Every Calculation
Every tax equalisation settlement turns on three figures. Firstly, there is hypothetical tax, the amount your employer withholds as your notional home-country cost. Secondly, there is actual tax, the real liability in both countries. Thirdly, there is the settlement, the balancing payment between you and your employer.
Understanding these three numbers gives you control of the process. In contrast, treating the policy as a black box guarantees surprises. Ultimately, the settlement is where every earlier assumption becomes cash.
Hypothetical Tax: The Deduction That Never Reaches a Tax Authority
Hypothetical tax sits at the heart of every tax equalisation policy, yet it is a payroll reduction rather than a tax payment. Your employer calculates what you would have paid had you never left home, then withholds that amount. Subsequently, the employer uses the money to fund your real liabilities in both countries.
The figure typically covers federal income tax, your home-state income tax, and the employee side of Social Security and Medicare. Furthermore, most policies strip out income the assignment did not generate. For instance, your investment portfolio and your spouse's earnings usually sit outside the calculation.
Crucially, hypo tax never reaches the IRS. It reaches your employer's balance sheet. Hence, it is a private cost-sharing device wearing the costume of a tax.
How Hypo Tax Changes Your Form W-2
Hypo tax reduces the wages reported in Box 1 of your Form W-2. It does not appear as a deduction anywhere on your return. Instead, it simply shrinks the gross figure before reporting begins.
This trips up sophisticated readers constantly. Specifically, executives look for a deduction line and cannot find one. However, the benefit already sits inside the reduced wage number.
Meanwhile, the employer adds back every payment it makes on your behalf. Therefore, UK tax settled by your employer becomes additional taxable compensation to you. The IRS guidance on taxable fringe benefits treats the discharge of your legal obligation as income, and that principle drives the whole structure.
Why Hypo Tax Is Never Creditable
You cannot claim a foreign tax credit for hypothetical tax. Equally, you cannot deduct it. No government received it, so no relief attaches to it.
Assignees occasionally try to include hypo tax on Form 1116. Consequently, they receive an IRS notice disallowing the claim. Only genuine foreign income taxes qualify, as the IRS foreign tax credit rules make clear.
Who Claims the Foreign Tax Credit When Your Employer Pays the Bill
Here sits the most valuable point in any tax equalisation arrangement. Your employer writes the cheque to HMRC. Nevertheless, you claim the foreign tax credit.
Many assignees assume the credit belongs to whoever paid. Actually, American law looks past the payer entirely. As a result, you receive credit for tax you never personally remitted.
This single rule is what makes the arithmetic work. Without it, employer-paid UK tax would be taxable to you with no offsetting relief. Accordingly, the assignment would become economically impossible.
The Technical Taxpayer Rule Under Regulation 1.901-2(f)
American law credits the person on whom foreign law imposes legal liability. The Treasury regulation at 26 CFR 1.901-2 states the rule directly: tax is considered paid by the person legally liable, even where another person remits it. Furthermore, the allowance-of-credit regulation at 1.901-1 confirms who may elect the credit.
British law imposes income tax on you, the employee. Your employer merely discharges your debt. Therefore, you remain the technical taxpayer and the credit is yours.
Practically, this means two entries move together. Firstly, the employer-paid UK tax increases your gross income. Secondly, the identical amount feeds Form 1116 as creditable foreign tax. Omitting either half produces a badly wrong return.
The Gross-Up Spiral and the Year-Two Problem
Employer-paid tax creates more taxable income, which creates more tax. Consequently, the calculation must gross up, layering tax upon tax until the series converges. This is arithmetic, not avoidance.
The timing compounds the difficulty. Your employer settles your UK liability months after the year closes. Meanwhile, that payment becomes American compensation in the year it is made, not the year it relates to.
Assignees therefore see income and credits landing in different years. In particular, a large UK payment in 2027 relating to 2026 lands on your 2027 return. Notably, IRS Publication 514 governs how the credit follows, and the ten-year carryforward often rescues the mismatch.
Modified PAYE, EP Appendix 6 and the Payments on Account Advantage
Most tax equalisation arrangements for inbound assignees run through a modified payroll. HMRC calls this an EP Appendix 6 agreement. Furthermore, your employer must apply for it, because it relaxes strict PAYE operation.
Under the arrangement, your employer estimates your annual grossed-up pay and benefits before the year begins. Subsequently, it pays one twelfth of the estimated liability each month. The HMRC guidance on modified PAYE in tax equalisation cases sets out the mechanics.
This matters to you personally. Specifically, it changes your British payment profile in a way that directly protects your American credit.
How the Appendix 6 Monthly Estimate Works
The best estimate includes annual salary, cash bonuses paid to 5 April, and non-cash benefits provided by the home employer. Additionally, it captures housing, school fees and relocation costs where the policy covers them. Your employer then trues up the figures after the year closes.
Actual earnings reach HMRC through your Self Assessment return by 31 January. Meanwhile, exact earnings and residual National Insurance go on a NIC Settlement Return by 31 March. The broader HMRC guidance on tax equalisation arrangements explains how the employer's undertaking operates.
Why Removing Payments on Account Protects Your Credit
Ordinary Self Assessment taxpayers make payments on account each January and July. Consequently, a first UK year can push roughly two years of British tax into a single American tax year. That bunching wrecks foreign tax credit planning for many expatriates.
Tax equalisation assignees escape this entirely. HMRC has used its powers under section 59A(9) of the Taxes Management Act 1970 to remove the payments on account obligation for everyone within a modified PAYE scheme. The HMRC Self Assessment manual on tax equalised employees confirms the concession.
Almost no commentary connects this British administrative rule to its American consequence. However, the effect is substantial. Because payments on account disappear, your UK tax lands in a smoother annual pattern, and your credit tracks your income far more closely.
HS212 and the Schedule HMRC Demands With Your Return
HMRC publishes a dedicated helpsheet for equalised employees. Furthermore, it imposes a reporting requirement most assignees never see, because their employer's provider handles it silently.
Reading it yourself is worthwhile. Specifically, it tells you exactly what your British return must contain.
What Goes in Box 1
The HMRC tax equalisation helpsheet HS212 requires Box 1 to carry an aggregate figure. It combines cash earnings, the cash equivalent of non-cash benefits taxed on a grossed-up basis, and the grossed-up tax on both.
Critically, HMRC then demands supporting detail. You must provide a full analysis of the Box 1 figure as a schedule with the return. Therefore, a bare number without the schedule leaves the return incomplete.
Notably, the helpsheet declines to explain how to gross up from a net position. HMRC assumes your adviser already knows. Consequently, the actual methodology sits entirely with your employer and its provider, which is precisely why you should review it.
The NIC Settlement Return Deadline
National Insurance follows a separate timetable from income tax. Your employer reports exact earnings and residual contributions by 31 March following the tax year. Additionally, Class 1A contributions on benefits carry their own 19 July deadline, with interest running on late payment.
Current thresholds sit in the HMRC rates and thresholds for employers 2026 to 2027. Furthermore, employee National Insurance is not creditable against American tax, a point we return to below.
FEIE or Foreign Tax Credit Under a Tax Equalisation Policy
Assignees frequently ask which relief their tax equalisation policy uses. In practice, the foreign tax credit does the heavy lifting in Britain. Nevertheless, the exclusion still appears on many returns.
Your employer's policy usually dictates the choice. Moreover, most policies require the provider to claim whichever combination minimises total cost, since the employer bears that cost.
The 2026 Exclusion Figures
For 2026, the foreign earned income exclusion reaches $132,900, up from $130,000 for 2025. Additionally, the housing amount limitation rises to $39,870. The IRS guidance on figuring the exclusion sets out the mechanics, and you claim it on Form 2555.
For a managing director earning several hundred thousand dollars, the exclusion barely moves the needle. Specifically, it shelters a modest slice and leaves the balance fully exposed. Therefore, the credit matters far more.
Why the Credit Usually Wins in Britain
British rates comfortably exceed American ones at senior levels. UK income tax reaches 45% above £125,140, while the personal allowance of £12,570 disappears entirely between £100,000 and £125,140. The GOV.UK income tax rates confirm the 2026/27 position, with thresholds frozen.
That 45% rate exceeds the 37% American top rate. Consequently, the credit usually eliminates American tax on employment income outright. Furthermore, it generates excess credits that carry forward for ten years.
Claiming the exclusion can actually reduce your credit, because excluded income cannot support a credit. Hence, on high London packages the exclusion often costs more than it saves.
Social Security, State Tax and the Gaps Your Policy Leaves Open
Tax equalisation policies cover assignment-related taxes. However, they rarely cover everything you owe. Understanding the gaps prevents unpleasant discoveries.
Totalisation and the Certificate of Coverage
The US-UK totalisation agreement stops you paying social security twice. Where your American employer seconds you temporarily, a certificate of coverage keeps you in the US system. Consequently, your employer pays FICA and you owe no UK National Insurance.
Your hypothetical tax normally includes the 6.2% Social Security and 1.45% Medicare employee shares. Therefore, you continue bearing your notional home cost. The Social Security Administration's US-UK agreement guidance explains the certificate process.
Where no certificate exists, you pay UK National Insurance instead. Importantly, National Insurance is not a creditable income tax for American purposes. As a result, that cost produces no foreign tax credit whatsoever.
The State Tax Your Hypo Never Covers
Your hypothetical tax assumes a stay-at-home state. Nevertheless, some states pursue you after departure regardless. California and New York are the most aggressive.
California grants no foreign earned income exclusion, no foreign tax credit, and no treaty relief. Similarly, New York applies a demanding domicile test to departing residents. Consequently, an unresolved state residency position can produce real tax that your policy never contemplated.
Review your state position before you leave, not afterwards. Furthermore, keep evidence of severed connections. Our cross-border planning specialists address this at the outset for every assignee.
A Worked Tax Equalisation Case Study With Real Numbers
Consider a US-citizen managing director relocating from New York to London on 6 April 2026. Their base salary is $450,000. Additionally, the employer provides UK housing worth $158,400 and covers school fees.
The employer withholds hypothetical tax of $128,000, covering notional federal tax, New York State and City tax, and the employee FICA shares. Therefore, the assignee receives $322,000 of net cash salary. That $128,000 represents their entire personal tax cost for the year.
All figures below use an illustrative exchange rate of £1 to $1.32.
The Settlement Calculation
Once grossed up, the assignee's British taxable earnings reach roughly £480,000. UK income tax and employee National Insurance come to approximately £198,000, which converts to about $261,360. The employer pays that amount directly to HMRC.
That payment becomes additional American compensation. Consequently, total US gross income reaches roughly $869,760, combining salary, housing and the employer-paid British tax. American tax before relief runs to approximately $295,000.
The assignee then claims the foreign tax credit for the full $261,360, because they remain the technical taxpayer. Residual American tax of roughly $34,000 remains, which the employer also settles. Subsequently, that $34,000 becomes taxable compensation in the following year, generating a further gross-up of around $12,600.
The employer's true additional cost therefore reaches roughly $180,000 beyond the headline package. Meanwhile, the assignee's cost stayed fixed at $128,000 throughout. That gap explains why employers scrutinise these policies so carefully.
The Repayment Trap in the Following Year
Tax equalisation settlements sometimes run the other way. Where withheld hypothetical tax exceeds the policy figure, the employer refunds you. Conversely, where it falls short, you repay the employer.
Repayments create a genuine American problem. You already paid tax on that compensation in an earlier year. Therefore, you need relief under the claim-of-right rules in section 1341 to recover it.
Critically, section 1341 relief compares your earlier tax with and without the repaid income. Where a foreign tax credit already reduced your earlier American tax to nil, the recomputation produces little or no benefit. Consequently, the credit that saved you in the assignment year can neutralise your relief in the repayment year, and few providers flag this before the settlement lands.
How TaxYork Can Help
TaxYork prepares American and British returns for senior assignees, investment bankers and company owners moving between the two countries. Furthermore, we work alongside employer-appointed providers, reviewing their computations rather than simply accepting them.
We check that employer-paid British tax appears correctly on both sides of your return. Additionally, we verify the gross-up methodology, the Box 1 schedule, and the credit position across assignment years. Our US tax return preparation service covers the full American filing, while our FBAR and FATCA specialists handle the foreign account reporting your assignment triggers.
Assignees often arrive with earlier years unfiled or wrongly filed. In those cases, we assess catch-up options and correct the historic position. Professional standards guidance from the ICAEW tax faculty, the Chartered Institute of Taxation and the AICPA informs how we approach every engagement.
Conclusion
Tax equalisation protects your economics, yet it complicates your compliance considerably. Your employer absorbs the extra cost of working abroad. However, you retain every filing obligation in both countries.
Three tax equalisation points deserve your attention above all others. Firstly, hypothetical tax reduces your reported wages and never generates relief. Secondly, you claim the foreign tax credit for British tax your employer paid, because British law makes you legally liable. Thirdly, the settlement timing shifts income and credits between years, and repayments can strand your relief entirely.
Modified PAYE brings a genuine advantage most advisers overlook. Because HMRC removes payments on account for equalised employees, your British tax lands more evenly and your American credit tracks it far better. Ultimately, reviewing your own numbers before signing anything remains the single most valuable step you can take. General guidance from MoneyHelper and background reading on the foreign tax credit at Investopedia provide useful orientation, though neither replaces specialist review.
Contact Us
Speak to a specialist before your tax equalisation settlement is finalised. You can book a consultation with our cross-border team at any stage of your London posting.
Email hello@taxyork.com or telephone 020 3488 8606. Furthermore, we review employer-prepared computations for assignees who already have a provider in place.
Disclaimer
This article provides general information only and does not constitute tax advice for any specific person or situation. Tax legislation, rates and thresholds change frequently, and their application depends entirely on individual circumstances. Figures quoted reflect the 2025/26 and 2026/27 British tax years and the 2025 and 2026 American tax years. Exchange rates used in the case study are illustrative. You should obtain professional advice before acting on anything contained here. TaxYork accepts no liability for any loss arising from reliance on this article.