An American in Bristol goes freelance. The first year's profit sits comfortably under the exclusion, the accountant confirms there is no US income tax to pay, and everyone moves on.
The bill that arrives is for self-employment tax, and nobody mentioned it. It is not small, it is not income tax, and the exclusion that removed the income tax does nothing to it.
This catches people every year, because the two charges look like one thing from the outside. They are not. One funds the Treasury, the other funds Social Security and Medicare, and only one of them responds to Form 2555.
The relief that does work is quieter and comes from a different place: the social security agreement between the two countries, which exists precisely so one person's work does not fund two systems.
So this guide sets out what the charge is, why the exclusion leaves it standing, how the agreement removes it, and what paperwork makes that stick.
What is self-employment tax?
A Social Security and Medicare charge on net earnings from self-employment. The IRS sets the combined rate at 15.3%: 12.4% for social security and 2.9% for Medicare. It starts at $400 of net earnings.
Why does the exclusion not remove it?
Because the two charges answer different questions. The exclusion takes foreign earned income out of the income tax calculation. Self-employment tax runs on net earnings from self-employment, and the IRS is explicit that you bring all of that income into the figure, including the part you excluded.
So a year can show no income tax and a substantial social security bill.
That is the single most common surprise in a first freelance year abroad.
In our practice it is also the easiest one to plan for, once somebody says it out loud.
Who actually pays it?
Self-employed US citizens and residents, wherever they live and whoever their clients are. A sole trader in Manchester with only British customers is within the charge in the same way as one in Boston. Nothing about the location of the work or the currency of the invoice changes that.
Employees are outside it, because their payroll taxes work differently.
However, a UK employee with freelance work on the side is inside it for the freelance part.
So the mixed case is the one worth checking carefully.
Partnership profits can also land here. A share of trading profit from a partnership is usually net earnings from self-employment in American terms, so the charge follows the share rather than the pay slip.
| Situation | US income tax | Self-employment tax |
|---|---|---|
| Freelance profit under the exclusion | Usually nil after Form 2555 | Charged in full |
| Freelance profit above the exclusion | Charged on the excess | Charged in full |
| UK National Insurance paid, certificate held | Unaffected | Removed by the agreement |
| Employed in the UK, no freelance work | Usually nil after the exclusion | Not in point |
How does the totalization agreement help?
It decides which country's system you contribute to, and only one of them. The IRS describes the point of these agreements as eliminating dual coverage and dual contributions for the same work. For somebody self-employed in Britain and paying National Insurance there, that generally means the British system.
The result is one set of contributions rather than two.
The IRS explains how the agreements operate and which countries have one.
So the relief is real, but it has to be claimed rather than assumed.
What is a certificate of coverage?
The document that proves which system covers you. The social security authority of the covering country issues it, and you show it when the other country asks why you are not contributing. For an American self-employed in Britain, it comes from HMRC.
Without it, the exemption is an assertion rather than a fact.
The IRS asks you to keep a copy with the return for each year you claim the exemption.
So the paperwork is light, but skipping it undoes the whole arrangement.
Does National Insurance count instead?
In substance, yes, and that is the arrangement working as intended. Contributing to the British system through Class 2 and Class 4 National Insurance builds a UK record, and the agreement stops the same earnings funding the American system at the same time.
The contributions themselves are not interchangeable, though.
National Insurance rates are set separately and buy British entitlements.
So you are not paying less in total; you are paying one system rather than two.
So keep both records in view. One of them funds a British pension and the other does not grow while the agreement applies, which is a sensible trade for most people and a poor one for somebody close to qualifying in America.
What happens to your US benefit record?
It stops growing for the years the British system covers. Contributions made in Britain count towards a UK pension rather than towards American credits, so a long freelance career abroad can leave gaps in the US record.
The agreement can help the two records talk to each other at claim time.
However, that is a benefits question rather than a tax one, and it deserves its own advice.
So check what each record shows before assuming either pension is secure.
Can you choose to keep paying into the US system?
Not as a free choice. The agreement allocates coverage according to the facts, not according to preference, so somebody genuinely self-employed and contributing in Britain cannot simply elect to fund the American system instead.
People ask because they want to protect their American credits.
That is a reasonable instinct and the wrong lever.
Voluntary contributions, where available in either system, are the route worth asking about instead.
Does the charge apply to a loss year?
No, because the charge runs on net earnings. A year with a loss produces no self-employment tax, and the $400 threshold means a very small profit produces none either. What it does not produce is a credit against other years.
Losses do not carry across to reduce the charge later.
Also, a loss year leaves a gap in whichever benefit record applies.
So a quiet year is cheaper, not free of consequence.
What about a US LLC or a UK limited company?
Changing the vehicle changes the question. Profits of a UK limited company are not net earnings from self-employment, so the charge never reaches them. Salary and dividends out of that company bring their own treatment on both sides.
A US LLC is a different matter again, because American tax usually looks straight through it.
Our guide to a US LLC and a UK resident member covers that mismatch.
So incorporating can move the charge, and it moves several other things with it.
Is there any deduction for the tax itself?
There is, on the income tax side. The IRS allows a deduction for the employer-equivalent portion when working out adjusted gross income, which softens the income tax effect of the charge.
It does not reduce the self-employment tax itself.
Nor does it help in a year where the exclusion has already removed the income tax.
So the deduction is worth most to people above the exclusion and worth nothing to those comfortably below it.
In short, treat it as an income tax deduction rather than relief from the charge. The distinction decides whether it is worth anything to you at all in a given year.
Which form reports it?
Schedule SE, filed with the annual return. The profit itself reaches the return through Schedule C for a sole trade, and Schedule SE then works out the charge on those net earnings.
Our guide to Schedule C for a UK sole trader covers the profit side.
You claim the exemption on the return itself and keep the certificate on file.
So the mechanics are simple once the coverage question is settled.
Also check the currency. Profit earned in sterling converts to dollars for the American return, so a strong pound can push a profit over a threshold that looked comfortably clear in the UK accounts.
Sorting out self-employment tax, step by step
A short sequence for a first freelance year abroad.
- Work out net profit from the self-employment, in sterling and then in dollars.
- Check whether that profit reaches the $400 point at which the charge begins.
- Establish which country's social security system your work falls under.
- Apply to HMRC for a certificate of coverage if the British system applies.
- Keep the certificate with the return for every year you rely on it.
- Review the position whenever you change country, client base or trading vehicle.
What if you have already paid it unnecessarily?
Then an amended return is usually the route, and the certificate is the evidence. Americans who freelanced in Britain for years without knowing about the agreement have often paid a charge the agreement would have removed.
There are time limits on reclaiming, so the older years may be closed.
Our guide to amending a US return from abroad sets out what that involves.
So check the open years first and treat the rest as a lesson rather than a project.
Does it interact with the foreign tax credit?
Barely, and that catches people out. The foreign tax credit relieves foreign income tax against American income tax. Self-employment tax is not income tax, so credits built up against it do not apply.
British National Insurance is not creditable against it either.
Our comparison of the exclusion and the foreign tax credit deals with the income tax choice.
So the social security charge has to be solved by the agreement, not by credits.
An illustrative example
Consider an American designer in Leeds, self-employed, with a profit comfortably below the exclusion in her first full year abroad.
Form 2555 removes her US income tax entirely. Schedule SE then charges 15.3% on the same profit, and she pays it, assuming it is simply what living abroad costs.
In her third year an adviser applies for a certificate of coverage, and the charge stops. Two earlier years are still open to amend.
These figures are illustrative. The sequence is the usual one: the exclusion works, the second charge goes unnoticed, and the fix was available all along.
Common mistakes we see
The first assumes no income tax means no return. The charge is reported on the same return and often stands alone.
The second claims the exemption without obtaining a certificate, which leaves nothing to show if anyone asks.
The third treats British National Insurance as creditable against the American charge. The agreement removes the charge; it does not credit against it.
The fourth forgets the charge when pricing freelance work, which quietly costs 15.3% of the first year's margin.
How US UK Tax Hub helps with self-employment tax
We settle the coverage question before the first return, because the answer decides whether the charge applies at all.
Where years have already gone by, we look at which are still open and whether amending them is worth the fee.
Our US federal returns service covers the filing, and fees stay fixed and agreed in writing. How we work sets out the process.
If you have gone freelance abroad, or are about to, talk to us before the first invoice.
