Self-Employed in the UK, Paying US Self-Employment Tax: The Complete Guide for American Expats

Self-Employment Tax Still Applies to Americans Abroad

If you're self-employed and a US citizen or resident alien, the IRS expects you to pay self-employment (SE) tax on your worldwide net earnings—even if you live and work entirely in the United Kingdom. This tax funds Social Security and Medicare, and it's one of the most commonly overlooked obligations for expats. Unlike income tax, which may be reduced by the Foreign Earned Income Exclusion (FEIE), SE tax is largely unavoidable. Understanding how it works, how to calculate it correctly, and when to file is essential to staying compliant and protecting your US retirement benefits.

How US Self-Employment Tax Works for UK-Based Americans

The Basics: What You Owe

Self-employment tax is calculated on your net profit from self-employment—roughly 15.3% of your net earnings. This breaks down as:

• 12.4% for Social Security (on income up to the current annual threshold)
• 2.9% for Medicare (no income cap)
• An additional 0.9% Medicare surtax applies if your modified adjusted gross income exceeds certain thresholds

You calculate SE tax using IRS Form Schedule SE. The self-employed pay both the employee and employer portions, though you may deduct half of your SE tax when calculating adjusted gross income.

Crucially, the IRS does not forgive SE tax based on where you earn your income. Even if you qualify for the Foreign Earned Income Exclusion (up to the current annual limit), you must still pay self-employment tax on the full amount of your self-employment income before applying any exclusion. This is a critical distinction that trips up many expats.

Calculating Your Net Self-Employment Income

Your net self-employment income is your gross business income minus allowable business deductions. As a self-employed person in the UK, you should be tracking:

• Professional fees and supplies
• Home office expenses (if you have a dedicated workspace)
• Travel and vehicle costs (be cautious with UK mileage allowance relief rules)
• Equipment and technology
• Professional development and memberships
• Insurance and accounting costs

You'll report this on IRS Form Schedule C, Profit or Loss from Business. The UK tax authority (HMRC) has parallel rules; you'll file a UK Self Assessment tax return as well, and the two regimes may not align perfectly—for instance, on home office deductions or depreciation schedules. Many expats find it essential to work with a tax professional who understands both systems.

Filing Requirements: US and UK Obligations

US Federal Filing Deadlines

As a self-employed American, you must file a US individual income tax return (Form 1040) by the current annual deadline—typically April 15 in the United States, or later if you request an extension. You'll include Schedule C (profit or loss) and Schedule SE (self-employment tax calculation). If you're abroad, you automatically receive a filing extension to the current deadline extension date (usually June 15), though interest will accrue on any tax owed after April 15.

If you've missed prior-year US tax returns, don't delay. The IRS penalty for not filing is severe, and expats can face both failure-to-file and failure-to-pay penalties. If you're concerned about prior years, our dedicated guide to missed US tax returns walks through your options, including the Streamlined Filing Compliance Procedures for unintentional non-compliance.

UK Self-Assessment

Simultaneously, you must register for UK Self Assessment with HMRC if your turnover exceeds the current threshold (confirm the latest figure with HMRC). You'll file a Self Assessment tax return annually, report your profits, and pay UK income tax and National Insurance contributions. HMRC's treatment of self-employed earnings and allowable deductions may differ from the IRS, so reconciling the two is crucial.

Other Filings: FBAR and FATCA

If you have UK bank or investment accounts totaling more than the current reporting threshold, you must file an FBAR (FinCEN Form 114) with the US Treasury by the current deadline. Additionally, if you hold certain foreign financial assets above the current threshold, FATCA (Form 8938) may apply. These are separate from income tax but equally non-negotiable.

The Foreign Earned Income Exclusion (FEIE) and Self-Employment Tax

Can You Use FEIE to Reduce SE Tax?

No—and this is the source of much confusion. The Foreign Earned Income Exclusion lets you exclude up to the current annual limit of foreign earned income from US federal income tax, but self-employment tax is calculated before the exclusion is applied. In other words:

• You pay SE tax on your full net self-employment earnings.
• You then apply FEIE to reduce your taxable income for income tax purposes.
• The result: you may owe little or no income tax, but you still owe the full SE tax.

This is one reason many self-employed expats find their US tax bill higher than expected. An employer abroad would pay half your payroll tax; as self-employed, you pay both halves.

Tax Treaty Considerations: US-UK

Double Taxation Risk

The US and UK have a tax treaty, but it primarily addresses income tax, not self-employment tax. Both countries may tax your self-employment income, leading to potential double taxation. However, you can claim a Foreign Tax Credit on your US return for UK income taxes paid (including National Insurance contributions, in some cases), which may offset your US income tax liability—though not your SE tax.

Proper structuring and documentation of these credits requires careful attention to eligibility rules and form completion (primarily Form 1118). This is another area where professional guidance is invaluable.

Quarterly Estimated Tax Payments

Do You Need to Pay Quarterly?

If you expect to owe US tax for the year, you should pay estimated quarterly taxes by the current deadlines (typically April 15, June 15, September 15, and January 15). This includes both income tax and SE tax. Paying quarterly helps you avoid penalties and keeps cash flow predictable.

Many self-employed expats underestimate their liability because they overlook SE tax or rely on outdated thresholds. Consulting a tax professional at the start of your business year to project your liability is wise.

Retirement Planning: Self-Employment Tax and Social Security

Building Your US Retirement Benefits

One silver lining: the SE tax you pay directly funds your US Social Security and Medicare benefits. Even abroad, paying SE tax helps you accrue qualifying credits toward future Social Security eligibility. If you're self-employed for a decade, you're building a claim on US retirement benefits that will follow you globally.

That said, if you're also covered by a UK pension scheme or National Insurance contributions, there may be bilateral social security agreements to consider. The US and UK have a totalization agreement to prevent double contributions and coordinate benefit eligibility; this is worth reviewing if you're planning a long-term move abroad.

Common Mistakes and Red Flags

What Often Goes Wrong

• Overlooking SE tax entirely and reporting only income tax on the UK return, leaving a gap when the IRS reconciles.
• Applying FEIE to SE tax, forgetting that it doesn't reduce SE tax liability.
• Misclassifying income (e.g., treating a UK salary as self-employment income when it should be W-2 equivalent), triggering unwarranted SE tax.
• Failing to file US returns for multiple years while abroad, accruing penalties and interest that compound annually.
• Not reconciling UK and US deductions, claiming deductions in both countries and triggering IRS scrutiny.

If you've missed prior-year US filings, the time to act is now. Our comprehensive resource on missed US tax returns explains your options, from simple catch-up filings to more complex procedures like the IRS Streamlined Filing Compliance Procedures for expats.

Working with a Cross-Border Tax Professional

Why It Matters

Self-employment tax calculations, FEIE eligibility, treaty planning, and multi-country deduction reconciliation are complex. Every filing is reviewed and signed by a licensed professional—a CPA or Enrolled Agent in the US, and a chartered accountant in the UK—to ensure both countries' rules are satisfied and your liability is minimized.

A cross-border specialist will:

• Model your liability under different scenarios (FEIE vs. Foreign Tax Credit, for example).
• Coordinate your UK Self Assessment with your US return to avoid inconsistencies.
• Ensure FBAR and FATCA filings are current and correct.
• Review estimated quarterly payments to avoid underpayment penalties.
• Advise on entity structure if you're considering incorporation or partnership.

Key Takeaways

• Self-employment tax (15.3%) applies to your worldwide self-employment income, regardless of location.
• The Foreign Earned Income Exclusion reduces income tax but not self-employment tax.
• You must file both a US return (Form 1040, Schedule C, Schedule SE) and a UK Self Assessment return.
• Quarterly estimated tax payments are necessary if you expect to owe tax.
• Double taxation is possible; proper use of Foreign Tax Credits and treaty provisions is essential.
• If you've missed prior-year US returns, filing now is critical; the penalties only grow with time.

Next Steps

If you're a self-employed American in the UK and haven't filed US returns in prior years, or you're unsure whether you're calculating SE tax correctly, don't navigate this alone. The rules are technical, the penalties are steep, and a single missed filing can trigger years of IRS correspondence. We recommend reviewing our detailed guide to missed US tax returns to understand your options, then scheduling a consultation with one of our cross-border tax specialists. We'll review your situation, quantify your liability, and put together a plan to get you compliant—and at ease.

Book a consultation with a Next Tax Source cross-border specialist today.

Frequently asked questions

Do I have to pay US self-employment tax if I'm living and working in the UK?

Yes. US self-employment tax applies to US citizens and resident aliens on worldwide net self-employment earnings, regardless of where you live. The tax funds Social Security and Medicare and is separate from income tax.

Can I use the Foreign Earned Income Exclusion to reduce my self-employment tax?

No. The FEIE reduces your taxable income for federal income tax purposes, but self-employment tax is calculated on your full net earnings before any exclusion is applied. You'll still owe the full SE tax even if FEIE eliminates your income tax liability.

What happens if I miss a year of US tax filing while abroad?

The IRS will charge failure-to-file and failure-to-pay penalties, plus interest, which compound annually. If this applies to you, our missed US tax returns guide explains your options, including catch-up filings and the Streamlined Filing Compliance Procedures for expats.

Do I need to file both a UK Self Assessment return and a US return?

Yes. You must file a UK Self Assessment return with HMRC and a US Form 1040 (with Schedule C and SE) with the IRS. The two jurisdictions have different deadlines and rules, so reconciling them is important.

What is the Foreign Tax Credit, and can it help offset my SE tax?

The Foreign Tax Credit lets you offset US income tax with UK income taxes paid, but it does not reduce self-employment tax. SE tax must be paid in full; the FTC reduces your income tax liability only. Proper form filing (Form 1118) is required.