Expats' Self-Employment Tax: An Overview for Wealthy US-UK Dual Filers
US self-employment tax is a 15.3% charge on your net trading profit, and the Foreign Earned Income Exclusion does not offset the self-employment tax that expats face. Wealthy US-UK dual filers usually escape it through the totalization agreement, paying UK National Insurance instead and attaching a certificate of coverage to the US return.
Why does self-employment tax blindside high-earning US expats?
Picture a London-based US citizen running a six-figure consultancy. Their accountant claims the Foreign Earned Income Exclusion, the US income tax bill drops to nothing, and everyone assumes the American filing is handled. A second figure, many thousand dollars in self-employment tax on income that has already been subject to UK tax, then shows up close to the bottom of the form.
Nobody mentioned it, and it reads like a fine for daring to work for yourself abroad.
That shock is common because self-employment tax sits in a different corner of the US Internal Revenue Code from income tax. It funds Social Security and Medicare rather than the general Treasury, and Congress deliberately walled it off from the reliefs expats lean on most.
Grasping that wall — and the treaty that lets you climb over it legally — is the difference between an ugly annual bill and a clean, single-system contribution record. For the wealthy dual filer with a growing practice, the numbers involved are rarely trivial.
What is the US self-employment tax, and who actually pays it?
Self-employment tax is the freelancer's version of the payroll taxes an employer and employee normally split between them. Because a sole trader is both boss and worker, they shoulder both halves. The IRS sets the combined rate at 15.3% on net earnings from self-employment, and it bites whether you live in Manhattan or Marylebone. In actuality, sole proprietors, independent contractors, and single-member LLC owners who bill clients under their own names are the most vulnerable self-employment tax filers.
Component
Rate
Applies to
Social Security
12.4%
Net SE earnings up to the annual wage base ($184,500 for 2026)
Medicare
2.9%
All net SE earnings, with no upper cap
Additional Medicare
0.9%
Income over $250,000 (married filing jointly) or $200,000 (single)
You calculate the trading profit on Schedule C, then compute the levy on Schedule SE. Only about 92.35% of your net profit is subject to the charge. You can deduct half of the resulting tax against your income, but the Social Security slice alone can still exceed $22,000 once profits exceed the wage base. For a high earner, that is a meaningful sum landing on top of a full UK tax bill.
The bill is the self-employment tax that expats still owe after the FEIE.
Under Internal Revenue Code section 911, the Foreign Earned Income Exclusion removes qualifying foreign wages and self-employment profit from your US income tax base. What it pointedly does not touch is the Social Security and Medicare charge. The statute excludes that income for income tax purposes only, so the self-employment tax expats who rely on the exclusion to zero out their federal bill still watch the full 15.3% land on the very same profit. It is entirely possible to owe zero US income tax and thousands in self-employment tax in the same year.
How the US-UK totalization agreement removes the charge
The genuine fix is a 1984 treaty, in force since 1985, known as a totalization agreement. The IRS explains its purpose plainly: to stop the same earnings being taxed for Social Security by two countries at once. The US-UK agreement assigns you to a single system, and for a self-employed person, that is normally the country where you actually live rather than where your passport was issued.
A UK-resident freelancer, therefore, pays UK National Insurance and is exempt from the US charge on the same earnings. This is where the self-employment tax expats living in Britain finally find their relief: you contribute to one national scheme, not both, and your Social Security record is protected under the treaty's totalisation rules for any future US benefit claim.
The certificate of coverage is your proof.
The exemption is not automatic. Recent US cases have confirmed that totalization agreements are not self-executing, which means you cannot simply leave the SE tax line blank and hope. You must hold a certificate of coverage showing UK National Insurance covers you.
Self-employed dual filers apply to HMRC through its overseas National Insurance service, then attach a copy of the certificate to the US return each year. The SSA's UK pamphlet sets out the same requirement from the American side. Secure the certificate before you file, because reconstructing it after a return has gone in is slow and stressful.
What you pay in the UK instead: Class 2 and Class 4
Swapping a US charge for a UK one is only sensible if you know the UK side. British self-employed contributions are paid through National Insurance, and the structure is far lighter at the top end than the US equivalent, because Class 4 is not uncapped in the same punishing way.
Contribution
Who pays
Broad effect
Class 2 NIC
Self-employed with profits above the small-profits threshold
Flat, low weekly amount protecting your state pension record
Class 4 NIC
Self-employed on profits above the lower profits limit
A main rate on profits within a band, then a reduced rate above the upper limit
Because the UK reduces the Class 4 rate above its upper profits limit, a wealthy consultant frequently pays less into the UK system than the US would have demanded through an uncapped Medicare charge plus the Social Security slice. The treaty does not merely prevent double payment; for many high earners, it steers them into the cheaper of the two regimes.
Foreign Tax Credit versus self-employment tax
A frequent and costly muddle is assuming the Foreign Tax Credit can absorb the SE charge. It cannot. The Foreign Tax Credit offsets US income tax with foreign income taxes you have paid; self-employment tax is a separate Social Security levy that the credit simply does not apply to.
UK National Insurance is not a creditable income tax either, so it cannot be used to reduce US income tax. Two different systems, two different reliefs — and only the totalization agreement bridges the SE side. Our guide to self-employed US expat tax walks through how these reliefs stack in a real return.
Watch-outs before you assume you are covered
Not every pound of income is self-employment income, and the self-employment tax expats are most likely to get wrong is most likely to fall into a few predictable groups. Landlords are the classic example: ordinary UK rental profit is generally investment income, not self-employment, so it usually falls outside the SE charge altogether — reporting it on Schedule C by mistake can manufacture a tax bill that never existed.
Single-member LLC owners are another trap. The US treats a single-member LLC as disregarded, so its trading profit flows straight onto your personal return as self-employment income, treaty exemption and all. Consultants who split time between countries need to assess their residence carefully, because the tie-breaker that determines their UK coverage depends on where they genuinely reside while performing the work. Get the residence position wrong, and the certificate of coverage may not hold up.
Partnership income deserves a second look, too. A partner's distributive share of a UK partnership's trading profit is generally self-employment income for US purposes, so a wealthy filer who has drifted from a sole trade into a partnership structure carries the same exposure and needs the same certificate.
Directors of US S-corporations sit in a different regime again, where a reasonable salary rather than SE tax drives the Social Security cost, so the planning levers are not identical across structures. The safest habit is to map each income stream to the correct US tax schedule before assuming the treaty covers it all.
How to check whether you are exposed this year
A short annual review usually settles the question before it becomes a filing problem. Run through the following before your return is prepared, and raise anything uncertain with an adviser while there is still time to obtain documentation.
- Confirm which income streams are genuinely self-employment income and which are investment, employment,t or passive income that was wrongly captured on Schedule C.
- Check that you are actually within the UK National Insurance scheme for the year, including any periods of arrival or departure that could split your coverage.
- Verify your certificate of coverage is current and matches the tax year on the US return, not a prior year.
- Separate the income tax analysis, where the Foreign Tax Credit and exclusion operate, from the social security analysis, where only the treaty helps.
- Recalculate if your profit has crossed the Social Security wage base or an Additional Medicare threshold, because the numbers at stake rise sharply at the top.
Wealthy dual filers rarely fail this review for lack of documents; they fail it for timing, discovering in April that a certificate they needed should have been requested months earlier. Building the check into your yearly rhythm removes most of that risk and keeps the treaty position clean and defensible.
Case study: a US-UK consultant escaping double contributions
Rachel is a US citizen who moved to Bristol and now runs a marketing consultancy through a UK sole trade, netting around £160,000 a year. Her first US return, prepared before she came to TaxYork, claimed the FEIE, showed no US income tax, and still reported roughly $11,000 of self-employment tax — a charge she was paying on top of full UK Income Tax and National Insurance.
The correction was straightforward once the treaty was applied. Rachel obtained a certificate of coverage from HMRC confirming she was within UK National Insurance, and her amended US return attached that certificate and removed the SE charge.
She now pays only UK Class 2 and Class 4 contributions, maintains a single protected pension record, and has stopped funding two social security systems for a single stream of work. The recovered $11,000 a year, compounded over a career, is the sort of leakage that quietly erodes a wealthy expat's balance sheet.
Talk to TaxYork before your next filing.
If you are self-employed on either side of the Atlantic and unsure whether the SE charge applies to you, get the position confirmed before you file, not after. Our US-UK dual-qualified team handles certificates of coverage, Schedule SE positions, and treaty analysis as a single, joined-up piece of work. Email hello@taxyork.com, call 020 3488 8606, or visit taxyork.com to arrange a review.