Introduction: Why Shadow Payroll Quietly Decides Your UK Tax Bill
A shadow payroll is a host-country payroll run purely to report and pay tax, while your actual salary continues to arrive from the home-country payroll. Furthermore, it is the mechanism almost every American executive seconded to London encounters, usually without being told. Your employer sets it up, your net pay looks unchanged, and the tax consequences land on you personally.
At TaxYork, we prepare returns for banking, private equity and technology executives on UK assignment. Consequently, we see the same failure repeatedly. The corporate payroll team runs the mechanics correctly, yet nobody explains what the arrangement does to the executive's own filing position. Therefore, this guide addresses the individual rather than the payroll department.
What a Shadow Payroll Actually Does
A shadow payroll does not pay you. Instead, it mirrors your home-country earnings inside a UK payroll so that PAYE and National Insurance reach HMRC on the correct amounts. Specifically, the UK reporting obligation attaches to the work you perform in Britain, regardless of which country issues the cheque. Additionally, the arrangement generates the P60 and P11D data that eventually populate your UK self-assessment return.
Why Executives Must Care Personally
Your employer carries the withholding obligation. However, you carry the filing obligation in both countries. Moreover, the timing of the tax your employer remits determines whether your US foreign tax credit works properly. That single interaction costs more money than every other issue in this article combined.
How Shadow Payroll Works Across Two Tax Systems
Understanding the mechanics takes five minutes and prevents years of confusion. Furthermore, the structure is simpler than the terminology suggests.
The Home Payroll Pays You, the Host Payroll Reports You
Your US employer continues paying your salary into your US account, deducting federal tax and applicable state tax. Meanwhile, the UK shadow payroll replicates those same earnings and calculates the PAYE due on your UK workdays. Consequently, HMRC receives tax on the correct figure without your bank details ever changing. The parallel payroll produces reporting, not payment.
You Are Not Paid Twice, and Not Taxed Twice
Executives frequently ask whether a shadow payroll doubles their income. It does not. Instead, one set of earnings appears in two reporting systems. Additionally, relief operates through the US-UK double taxation treaty and the foreign tax credit. Therefore, the same income is not taxed twice over. Nevertheless, relief requires correct claims on both returns, and those claims do not happen automatically.
Where Your Form W-2 Fits
Your W-2 continues reporting worldwide wages to the IRS, because US citizens remain taxable on global income. Furthermore, the UK shadow payroll figures rarely reconcile neatly to the W-2, since the two tax years differ. Britain runs from 6 April, while the United States runs to 31 December. Accordingly, every reconciliation involves apportioning across two overlapping periods.
Modified PAYE Under EP Appendix 6
Most tax-equalised assignments operate a modified PAYE scheme rather than a standard one. Specifically, HMRC permits this under EP Appendix 6, and it changes how your shadow payroll behaves throughout the year.
Who Qualifies for the Arrangement
EP Appendix 6 suits foreign national employees sent to work in the UK under a tax equalisation agreement. Moreover, the employer must undertake to meet the UK income tax liability on general earnings and operate PAYE on a grossed-up basis. HMRC sets out the conditions in the PAYE manual at PAYE82002. Applications use forms that the CIPP tracks each year.
The Best Estimate and the Monthly Twelfth
Under modified PAYE, your employer estimates total cash earnings and benefits for the year, then grosses that figure up. Consequently, the employer pays one twelfth of the estimated PAYE each month, by the 19th or 22nd of the following month. Employers covering five or fewer employees may pay quarterly instead. Importantly, the 50% overriding limit does not apply to these calculations.
The Deadlines That Routinely Slip
An in-year review runs from December to April, catching bonuses, share awards, arrivals and leavers. Furthermore, the P60 deadline falls on 31 May after the tax year ends, while forms P11D are due by 31 January following the tax year. That January date matters enormously to you, because your actual UK figures often arrive after your US return is already filed.
The April 2025 Section 690 Overhaul Nobody Told You About
Here is the change that most published guidance still ignores. From 6 April 2025, the section 690 process changed fundamentally, and the effect on any shadow payroll is immediate.
From Direction to Notification
Previously, employers applied to HMRC for a section 690 direction permitting PAYE on a reduced proportion of earnings. Now, employers submit an online notification instead. Additionally, HMRC's PAYE manual at PAYE81514 confirms that the notification takes effect from the date HMRC acknowledges receipt. Therefore, the waiting period that previously delayed assignments has largely disappeared.
Your Old Direction Has Already Expired
Directions issued before 6 April 2025 ceased to be effective from that date. Consequently, employers relying on a pre-2025 direction have been over-withholding or under-withholding ever since. Moreover, a fresh notification is required for each tax year, using the HMRC section 690 service. We check this for every new client, and we frequently find it missing.
Who the Notification Covers
Employers may notify for employees who are non-UK resident or eligible for split-year treatment. Furthermore, the process covers those treated as non-resident under a double taxation agreement, and those eligible for Overseas Workday Relief. Additionally, the employer specifies a non-PAYE proportion representing its best estimate of non-UK duties. That estimate should be revisited whenever your travel pattern changes materially.
Overseas Workday Relief After the FIG Reform
Overseas Workday Relief changed profoundly on 6 April 2025. Consequently, older guidance about offshore accounts and remittances is now actively misleading.
The Four-Year Qualifying New Resident Window
Relief now depends on qualifying new resident status rather than a remittance basis claim. Specifically, you must be UK resident having been non-UK resident for at least ten consecutive tax years beforehand. Relief then runs for the first year plus up to three further consecutive UK resident years. The Low Incomes Tax Reform Group explains the mechanics clearly, and Tax Adviser magazine covers the wider FIG regime.
The 30% and £300,000 Cap
Relief is capped at the lower of 30% of your worldwide employment income or £300,000 per qualifying year. Additionally, relieved earnings no longer need to sit in an offshore account, and you may bring the money to Britain freely. Nevertheless, the cap bites hard on the largest packages, which is precisely where a shadow payroll is most likely to operate.
The Price Additional-Rate Earners Do Not Pay
Claiming the relief costs you your personal allowance and your capital gains annual exempt amount for that year. However, here is the point advisers rarely make. If your income already exceeds £125,140, your personal allowance has tapered to nil regardless. Therefore, the election is effectively free for most executives running a shadow payroll, and failing to claim it simply discards money.
National Insurance, FICA and the Certificate of Coverage
Social security follows entirely separate rules from income tax. Consequently, a correct shadow payroll answer on tax tells you nothing about your contributions position.
Appendix 7A and the NIC Settlement Return
Employers operating modified PAYE may also apply to calculate National Insurance on a modified basis under EP Appendix 7A. Under that arrangement, the employer accounts for contributions on a best estimate of earnings attracting Class 1 liability. Furthermore, exact figures and residual contributions go to HMRC on a NIC Settlement Return by 31 March following the tax year end.
The Certificate That Stops Double Contributions
The US-UK totalisation agreement prevents paying into both systems simultaneously. Specifically, a certificate of coverage confirms which country's scheme covers you, and the IRS explains totalisation agreements here. Additionally, HMRC sets out the National Insurance position for work abroad. Without one, your employer keeps deducting FICA while HMRC also charges National Insurance.
Employer Contributions at 15%
Employer National Insurance runs at 15% on earnings above a secondary threshold of £5,000 for 2026/27. Moreover, that threshold fell sharply from £9,100 in 2024/25. Consequently, the employer cost of a UK assignment rose materially, which increasingly shapes whether companies approve secondments at all.
Short-Term Assignments: Appendix 4 and Appendix 8
Not every American working in Britain needs a full shadow payroll. Furthermore, two HMRC arrangements exist precisely to avoid one.
The Sixty-Day Rule for Business Visitors
An Appendix 4 short-term business visitor agreement lets a UK employer exempt qualifying overseas employees from PAYE during UK business visits. Additionally, HMRC operates a sixty-day concession where UK costs are borne locally, provided the days do not form part of a more substantive period. Integration into the UK business defeats the concession entirely.
When Treaty Relief Is Unavailable
Where treaty relief fails for employees spending sixty days or fewer in Britain, Appendix 8 permits annual PAYE accounting. Consequently, the employer reports and pays by 31 May following the tax year end. Grant Thornton summarises the practical thresholds, though the analysis of your own position still belongs on your return.
Where Shadow Payroll Goes Wrong for the Individual
Corporate compliance and personal compliance diverge sharply here. Moreover, the divergence costs executives real money every year.
The Foreign Tax Credit Timing Mismatch
This is the most expensive problem we see. Your UK tax accrues across a year ending 5 April, while your US return covers the calendar year. Furthermore, modified PAYE settles final figures as late as the following 31 January. Consequently, cash-basis foreign tax credit claims routinely misalign, stranding credits in the wrong year. The section 905(a) accrual election fixes this, but it binds you permanently, so we model it before filing your US tax return.
Tax Equalisation and Hypothetical Tax
Under equalisation, your employer deducts a hypothetical US tax and pays your actual UK liability. Therefore, your payslip deduction is not a real tax payment and generates no foreign tax credit. Additionally, the UK tax your employer pays on your behalf is itself taxable earnings, which is why the gross-up exists. Executives who treat hypothetical tax as creditable overstate their credit and invite an IRS adjustment.
Case Study: A Managing Director Seconded to London
Consider Rachel, a US bank managing director seconded from New York on 6 April 2026 under a tax equalisation agreement. Her package totalled $1.05 million, comprising $650,000 base and a $400,000 bonus. Her employer operated an EP Appendix 6 shadow payroll alongside her continuing US payroll.
Converted at 0.77, her UK employment income reached £808,500. Her personal allowance tapered to nil. Consequently, UK tax before relief came to £345,000, being £7,540 at the basic rate, £29,948 at 40% and £307,512 at the additional rate. Rachel spent roughly a quarter of her workdays outside Britain, producing £202,125 of overseas workdays.
Because that figure sat below both the 30% and £300,000 caps, Overseas Workday Relief applied in full, saving £90,956. Furthermore, the election cost her nothing, since her personal allowance had already tapered away. Her employer had also failed to submit a fresh section 690 notification. Consequently, PAYE ran on her entire salary rather than the reduced proportion. We corrected both points and realigned her foreign tax credit year, converting a projected US balance due into a refund position.
How TaxYork Can Help
We act for the executive, not the payroll provider. Specifically, we confirm whether your employer filed a current section 690 notification. Additionally, we test your qualifying new resident status. We then quantify Overseas Workday Relief before the year closes, rather than afterwards.
Furthermore, we reconcile your UK shadow payroll figures to your Form W-2 and model the foreign tax credit across both tax years. Our cross-border planning service handles the assignment structure, while we resolve any reporting gaps on foreign accounts through our FBAR and FATCA service.
Executives arriving with unfiled prior years are common, particularly where an earlier assignment went unreported. Accordingly, we bring those years current through the IRS Streamlined Filing service before HMRC or the IRS raises the question.
Conclusion
A shadow payroll is a reporting mechanism, not a tax charge. Nevertheless, it determines when your UK tax is paid, which in turn determines whether your US foreign tax credit lands in the right year. Executives who treat the arrangement as their employer's problem consistently overpay.
Three actions matter most this year. First, confirm your employer filed a section 690 notification for 2026/27, because pre-2025 directions expired. Second, test whether you qualify for Overseas Workday Relief, and claim it where your personal allowance has already tapered to nil. Third, obtain a certificate of coverage so that FICA and National Insurance do not run in parallel. Above all, align your two tax years deliberately rather than by accident.
Contact Us
Beginning or midway through a UK assignment? We would welcome the conversation. Please book a consultation and we will review your payroll position alongside both returns.
Email hello@taxyork.com or telephone 020 3488 8606. Additionally, professional guidance comes from the CIOT, the ICAEW and the AICPA. Meanwhile, HMRC and MoneyHelper publish free guidance for UK arrivals.
Disclaimer
This article provides general information about shadow payroll arrangements and related US-UK tax obligations. It does not constitute tax advice and you should not rely on it for any specific transaction. Tax rules change frequently and their application depends entirely on individual circumstances. Please obtain professional guidance before acting. TaxYork accepts no liability for any loss arising from reliance on this content.