Introduction: Inside IR35 and the Bill Americans Pay Twice
Being inside IR35 already costs a British contractor twenty to thirty per cent of their take-home pay. For an American consultant working in London, however, the damage runs considerably deeper. Furthermore, almost nothing written on the subject acknowledges that a second tax system is watching the same money.
The reason is structural. HMRC recharacterises your fees as employment income. The IRS, meanwhile, applies its own classification rules and reaches its own conclusion. Consequently, one engagement can be employment in Britain and self-employment in America at the same instant. That mismatch drives the real cost.
At TaxYork we prepare returns for consultants, contractors and interim executives who move between the two systems constantly. In our experience, the most expensive errors are not the UK ones. Rather, they sit on the US return, where a misread payslip quietly overstates income by fifteen per cent every single year.
This guide covers the UK mechanics in full, then the US consequences that no British contractor guide addresses. Additionally, it sets out how to recover tax already overpaid, and what to do when several years of US filings have been missed altogether.
What Inside IR35 Actually Means for an American in Britain
An engagement sits inside IR35 when the working relationship resembles employment rather than genuine business-to-business supply. HMRC examines control, personal service and mutuality of obligation. Notably, the written contract matters far less than what actually happens day to day.
The consequence is mechanical. Your fee-payer deducts income tax and employee National Insurance before you receive anything. Therefore, money that once arrived gross into your company now arrives net, taxed at source under PAYE. HMRC explains the framework in its off-payroll working guidance.
Importantly, the label attaches to the engagement, not to you. Accordingly, you can be inside IR35 on one contract and outside it on another in the same tax year. Each determination stands alone, and each carries its own US consequences.
Why the US Side Does Not Follow the UK Determination
Here is the point that catches nearly every American out. Being inside IR35 changes nothing about how the IRS classifies you. The United States applies its own common-law test, set out in IRS guidance on worker classification, and it does not defer to HMRC.
In practice the two systems often disagree. HMRC may treat you as a deemed employee while the IRS still sees an independent contractor filing Schedule C. Consequently, you can face PAYE in Britain and self-employment tax in America on identical earnings.
The good news is that this outcome is fixable. However, it is fixable only if you identify it before filing, rather than three years later when a notice arrives. Therefore, the classification question deserves attention at the moment the determination lands, not at the end of the tax year.
How an Inside IR35 Determination Is Made and Who Makes It
Since April 2021, medium and large private-sector clients decide status themselves under Chapter 10 of ITEPA 2003. Public authorities have done so since April 2017. Meanwhile, small clients remain under the older Chapter 8 rules, where your own company decides.
That split matters enormously, because it determines who carries the risk and which calculation applies. Furthermore, it changed materially on 6 April 2026.
Status Determination Statements and the Client's Duty
A client inside the regime must issue a Status Determination Statement. The statement must give the conclusion and the reasoning behind it. Additionally, the client must pass it to you and to any agency in the chain.
You may challenge it. Specifically, the client has 45 days to respond to a disagreement, either confirming the original view or replacing it. Many blanket determinations collapse under a properly evidenced challenge, particularly where substitution rights are genuine.
Clients frequently rely on the Check Employment Status for Tax tool. Nevertheless, the tool returns an undetermined result in a meaningful minority of cases, and it only binds HMRC where the answers given were accurate.
The 6 April 2026 Threshold Rise That Hands Status Back to You
On 6 April 2026 the small-company thresholds rose substantially. Turnover moved from £10.2 million to £15 million, and the balance sheet total from £5.1 million to £7.5 million. The employee test stayed at fifty, and a client must exceed two of the three.
Around fourteen thousand clients therefore fall out of the regime, as ICAEW has documented. For those engagements, responsibility for deciding whether you are inside IR35 returns to your own company under Chapter 8.
There is a timing quirk worth knowing. Company size is tested on the prior financial year, so most affected engagements only feel the change from April 2027. Consequently, do not assume the rules have already moved in your favour.
The Wholly Overseas Client Exemption
If your end client has no UK presence, the off-payroll rules do not apply at all. HMRC confirms in manual ESM10006 that a client with no UK residence and no UK permanent establishment sits outside Chapter 10 entirely.
This exemption is enormously relevant to Americans in Britain. Many bill US parent companies, US private equity houses or US technology firms directly. In those cases your own company self-assesses, and a determination that you are inside IR35 never arrives from the client at all.
Be careful, though. A UK subsidiary, branch or permanent establishment destroys the exemption. Therefore, check the contracting entity rather than the brand on the letterhead.
What Inside IR35 Costs You in the UK in 2026/27
The UK arithmetic is unforgiving, and most contractors underestimate it because they measure against the wrong number. Specifically, they compare their day rate to their old net income, forgetting what the fee-payer removes before PAYE even starts.
The Deemed Direct Payment and PAYE at Source
Where Chapter 10 applies, the fee-payer treats your fees as a deemed direct payment. Income tax follows the ordinary bands: twenty per cent, then forty per cent above £50,270, then forty-five per cent above £125,140. The personal allowance of £12,570 tapers away entirely once income passes £125,140.
Employee Class 1 National Insurance applies at eight per cent between £12,570 and £50,270, then two per cent above. Consequently, a well-paid consultant sees a marginal rate of forty-seven per cent long before the contract ends.
Under Chapter 8, by contrast, your company calculates a deemed employment payment at the year end. The mechanics differ, but the destination is similar. HMRC sets out the steps in manual ESM8175.
One relief does survive intact. Employer pension contributions made through the deemed employer's payroll still reduce the taxable amount, and MoneyHelper explains the annual allowance limits that apply. Therefore, salary sacrifice remains the most effective lever left to a contractor caught by the rules.
Employer National Insurance Comes Out of Your Rate
This is the cost that never appears on a payslip as yours. Employer National Insurance runs at fifteen per cent above a £5,000 secondary threshold for 2026/27, and the apprenticeship levy adds another half a per cent. The rates sit in the HMRC employer thresholds guidance.
Economically, you bear it. Agencies build employer NIC into the assignment rate they quote, so the headline figure is not your gross wage. Rather, your gross wage is what remains after those employer costs are stripped out.
Solve the arithmetic before you accept a rate. On a £240,000 annual assignment rate, gross taxable pay is roughly £208,400 once employer NIC and the levy are removed. Therefore, more than £31,000 vanishes before a single band of income tax applies.
The 5% Allowance That Only Survives Under Chapter 8
Contractor guides routinely promise a flat five per cent allowance against the deemed payment. Importantly, that allowance only survives under Chapter 8, where your own company runs the calculation. It was removed for public-sector engagements in 2017 and does not feature in the Chapter 10 deemed direct payment at all.
Accordingly, the 2026 threshold rise quietly restores the allowance for engagements that drop back into Chapter 8. On £200,000 of relevant income, five per cent is £10,000 of relief that a Chapter 10 contractor simply cannot claim.
For a US filer there is a sting attached. The allowance reduces the UK deemed payment, but the IRS taxes what you actually received. Consequently, the two figures diverge, and the foreign tax credit calculation must reconcile them rather than assume they match.
The US Return: Where the Double Tax Actually Happens
Now to the part that British contractor guides omit entirely. Being inside IR35 reshapes your US return in three separate places, and each one can cost five figures if handled badly.
Employee or Self-Employed? The IRS Decides Separately
Start with classification, because everything else follows from it. If the IRS treats you as self-employed, your earnings land on Schedule C and attract self-employment tax. If it treats you as an employee, they are wages, and Schedule SE never opens.
A Chapter 10 engagement usually supports employee treatment on the US side too, since the deemed employer withholds and reports through real PAYE. A Chapter 8 engagement is far weaker, because your own company pays you. Therefore, the same phrase — inside IR35 — produces different US answers depending on which chapter applies.
Get this wrong in the generous direction and you underpay by roughly fifteen per cent. Get it wrong in the cautious direction and you hand the IRS tax the treaty never required.
Self-Employment Tax and the Certificate of Coverage
Self-employment tax runs at 15.3 per cent of 92.35 per cent of net earnings. Social Security applies to the first $184,500 for 2026, while Medicare at 2.9 per cent is uncapped and an extra 0.9 per cent applies above $200,000. On a substantial consulting income, that charge exceeds $30,000.
The US-UK totalisation agreement removes it entirely. Because you pay National Insurance in Britain, you are covered by the UK system alone, as the IRS totalization agreements page confirms. The relief is not automatic, however.
You need an HMRC certificate of coverage, attached to your Form 1040 each year with a statement citing the agreement. Additionally, where HMRC will not issue one, Revenue Ruling 92-9 provides an alternate procedure that almost no competitor page mentions. The SSA agreement summary explains the coverage rules in detail.
Foreign Tax Credit Sourcing and the Uncreditable Employer NIC
Only some of your UK burden generates a US credit. UK income tax qualifies. Employee National Insurance does not, because contributions are social security payments rather than creditable income taxes, and the totalisation agreement handles them instead.
Employer National Insurance fails twice over. It is not an income tax, and it is not legally your liability at all. Consequently, the £31,000 stripped from a £240,000 assignment rate delivers no US relief whatsoever, which is precisely why being inside IR35 hurts an American more than a Briton.
Claim what remains on Form 1116, in the general category basket. The IRS foreign tax credit guidance sets out the limitation calculation that caps the claim.
Timing, Baskets and the Credit You Nearly Lose
Even a correctly computed credit can be stranded by timing. Fortunately, one feature of being inside IR35 works firmly in your favour, and most filers never notice it.
Why PAYE Fixes the Payments on Account Problem
Self-assessment taxpayers pay UK tax in lumps, including payments on account each January and July. On the cash basis, two years of UK tax can land in a single US calendar year. The result is a credit surplus in one year and a shortfall in the next.
PAYE removes that distortion completely. Because the fee-payer withholds as you earn, UK tax accrues evenly across the year. Therefore, being inside IR35 aligns your UK payments with your US calendar year far better than outside-IR35 trading ever did.
That alignment is worth real money. Consequently, filers who previously used the section 905(a) accrual election to smooth bunching may no longer need it, although the election is irrevocable once made.
The 2024 Set-Off Rules and Your Foreign Tax Credit
From 6 April 2024, HMRC can set off tax you or your company already paid against a deemed employer's PAYE liability. The relief applies where a status determination is later corrected. Furthermore, it reaches deemed direct payments made on or after 6 April 2017, provided the trigger event falls after April 2024. HMRC explains commencement in manual ESM10037.
This fixes UK double taxation. It does nothing for your US return, however, and it can actively harm it. Specifically, a set-off can reduce the tax you are ultimately treated as having borne, which shrinks the creditable amount claimed years earlier.
That is a foreign tax redetermination. Accordingly, section 905(c) obliges you to notify the IRS, and failing to do so carries penalties independent of the tax at stake. Few contractors realise a UK correction can force a US amendment.
FEIE Versus Foreign Tax Credit When You Are Inside IR35
The foreign earned income exclusion caps at $132,900 for 2026. On a consulting income well above that, exclusion alone leaves a substantial balance exposed. Additionally, the exclusion never shelters self-employment tax.
For most consultants inside IR35, the foreign tax credit wins decisively. An effective UK rate approaching thirty-eight per cent comfortably exceeds US rates, so the credit eliminates residual US tax and generates carryforward besides. The IRS exclusion guidance sets out the qualifying tests.
Think carefully before revoking an existing exclusion election, though. Revocation locks you out for five tax years without IRS consent. Therefore, model both routes across the full contract term rather than a single year.
Reporting Duties That Survive an Inside IR35 Determination
Going inside IR35 does not retire your company, and it certainly does not retire your reporting obligations. On the contrary, a dormant personal service company creates precisely the filings people forget.
FBAR and Form 8938 for the Dormant Company
Your company's UK bank account remains a foreign financial account. If your aggregate foreign balances exceed $10,000 at any point, you file an FBAR, and signature authority alone triggers the duty. Penalties reach $16,536 for non-wilful failures and $165,353 where wilfulness is alleged.
Form 8938 sits alongside it under different thresholds. Living abroad, you report where specified foreign assets exceed $200,000 at year end or $300,000 at any time, doubled for joint filers. Notably, the two forms overlap without replacing one another, which is why our FBAR and FATCA reporting service treats them as a single exercise.
The Company You Stopped Using Still Files
A UK company you control remains a controlled foreign corporation for US purposes. Consequently, the Form 5471 duty continues while the company exists, even with no trading activity and no distributions.
Many consultants stop filing the moment the contract goes inside IR35, assuming an idle company is invisible. It is not. Furthermore, information-return penalties start at $10,000 per form per year and run independently of any tax owed, so striking the company off promptly is often the cheaper answer.
Case Study: A US Consultant Moved Inside IR35 in London
Consider a client we will call Dana, an American technology consultant contracting through a personal service company. In April 2026 their bank client issued a Status Determination Statement placing the engagement inside IR35. The assignment rate stayed at £240,000 for the year.
The fee-payer stripped employer costs first. Employer National Insurance of £30,516 and an apprenticeship levy of £1,042 came out, leaving gross taxable pay of £208,441. Dana never saw the missing £31,558, yet their agency statements kept quoting £240,000.
UK income tax on that gross pay came to £80,001, with the personal allowance fully tapered away. Employee National Insurance added £6,179. Net UK receipts were therefore £122,261, against a headline rate that had promised far more.
On the US return, the first error was the obvious one. Dana's previous preparer had reported the full £240,000, overstating US income by more than £31,000 — roughly $41,600 at prevailing rates. That inflation distorted the Form 1116 limitation every year it was repeated.
The second error cost more. Because the preparer treated Dana as self-employed on Schedule C, self-employment tax of just over $30,000 appeared, despite full UK National Insurance coverage. A certificate of coverage removed it entirely.
Correcting both, creditable UK income tax of roughly $105,400 against US wages of about $274,600 produced an effective UK rate near thirty-eight per cent. Consequently, no residual US tax arose, and a general-category carryforward emerged for later years. We amended within the ten-year window that section 6511(d)(3) allows for foreign tax credit claims.
Missed Filings: Catching Up After Years Inside IR35
Many consultants only discover the problem after several years. Fortunately, structured relief exists, and it works well for exactly this fact pattern.
Streamlined Foreign Offshore Procedures
Where the failure was non-wilful, the IRS Streamlined Filing Compliance Procedures remove the offshore penalty entirely for qualifying non-residents. You file three years of amended or delinquent returns, six years of FBARs, and a Form 14653 certification explaining the failure.
A misunderstood inside IR35 determination supports a genuine non-wilful narrative. After all, PAYE was deducted at source, tax was demonstrably paid to HMRC, and no income was hidden anywhere. Our IRS Streamlined Filing service builds that certification from the payroll evidence.
Amending to Recover Overpaid US Tax
Separately, where you paid US tax you never owed, amendment recovers it. Foreign tax credit claims enjoy a ten-year window rather than the ordinary three, which reaches back much further than most filers expect.
Self-employment tax refunds are different, however. Those follow the ordinary three-year limit, so a wrongly paid SECA charge expires far sooner than a missed credit. Therefore, address the self-employment tax question first when triaging several open years.
How TaxYork Can Help
We prepare US and UK returns for consultants, interim executives and company owners across both systems. Consequently, we read a Status Determination Statement and a Form 1116 with equal fluency, which is unusual and, on this topic, decisive.
Our work on an inside IR35 engagement begins with the payslip arithmetic. We establish true gross wages, separate creditable income tax from non-creditable National Insurance, and settle the US classification question before anything is filed. Additionally, we secure the certificate of coverage that removes self-employment tax.
Where years have been missed, we handle the catch-up end to end through our US tax return preparation service. Additionally, where the wider structure needs attention, our cross-border planning service takes over. We do not hand you a checklist. Instead, we prepare, file and defend the position.
Our team follows the technical debate closely, including the Chartered Institute of Taxation's employment status work and the statutory text of Chapter 10 of ITEPA 2003 itself. Consequently, we argue from the legislation rather than from a summary of it.
Conclusion
Being inside IR35 is a UK determination with unmistakably American consequences. Furthermore, the largest costs never appear on a UK payslip. Employer National Insurance earns no credit. The IRS decides your classification for itself. Additionally, a self-employment charge often survives that a certificate of coverage would have removed.
The remedies are concrete. Establish true gross wages rather than the assignment rate. Separate creditable tax from National Insurance. Obtain the certificate of coverage. Additionally, watch for UK corrections that force a section 905(c) redetermination on the US side.
Above all, act while the windows remain open. Ten years for foreign tax credit claims is generous, yet three years for self-employment tax refunds is not. Ultimately, an engagement inside IR35 rewards precision, and precision here is worth tens of thousands.
Contact Us
Speak to a specialist who prepares both returns rather than one. To review an engagement that has moved inside IR35, or to catch up on missed US filings, book a consultation with our team today.
Email hello@taxyork.com or call 020 3488 8606. Furthermore, if several years remain unfiled, raise it at the outset, because sequencing the claims correctly protects the refunds with the shortest deadlines.
Disclaimer
This article provides general information on UK and US tax rules current at August 2026 and does not constitute tax advice for any specific person or engagement. Tax outcomes depend entirely on individual circumstances, contract terms and residence status. Accordingly, you should obtain professional advice before acting. TaxYork accepts no liability for action taken solely in reliance on this content.