You registered with a GP months ago. Your National Insurance comes out of your payslip, the NHS looks after your family, and Medicare feels like something that belongs to a country you left. Then your accountant mentions Medicare tax, and the year suddenly looks more complicated.
The confusion is understandable, because two different systems share one word. Medicare tax is a payroll charge collected under US social security law. Medicare cover is a benefit administered by a different agency under different rules. Moving to Britain changes your relationship with both, though not in the same way or at the same time.
This article deals with the tax side only. In our practice, that is where the avoidable cost sits: people either pay a charge they were exempt from, or skip one the treaty was never going to relieve.
What is Medicare tax?
Medicare tax is a US payroll charge on earnings. Employers and employees each pay a share, and the self-employed pay both halves through self-employment tax. It funds the Medicare programme. Critically, it is a social security charge rather than an income tax, which is why the income tax treaty does not touch it.
Does the NHS change what you owe?
Using the NHS does not change a line of your US return. The social security agreement does. It decides which system your earnings belong to. Paying National Insurance usually settles the question, because one set of earnings belongs to one system.
So the NHS is relevant only because it sits behind National Insurance, and National Insurance is the evidence that Britain has taken your earnings into its system. That is a narrow point, though it is the one that does the work.
Which country collects the Medicare tax?
The US and the UK have a social security agreement. Most people call it a totalisation agreement. The IRS explains that these agreements exist to avoid double taxation of the same earnings. So you check the agreement first, before you decide whether the US charge applies at all.
The general pattern is simple. Work performed in Britain for a British employer belongs to the UK system, so National Insurance applies and US Medicare tax does not. A posting that stays short and stays with a US employer can run the other way for a limited period.
Our longer piece on how the US-UK totalisation agreement works walks through the detached worker rules and the certificate that proves them.
| Situation | Which system normally collects | What proves it |
|---|---|---|
| Employed in Britain by a British employer | UK National Insurance | Payslips and P60 showing NIC deducted |
| Posted to Britain short term by a US employer | US Social Security and Medicare tax | Certificate of coverage from the US authority |
| Self-employed and working in Britain | UK National Insurance, once the agreement is claimed | Certificate of coverage from HMRC |
| Self-employed in Britain with no certificate | The IRS charges self-employment tax | Nothing — which is the problem |
Does the foreign earned income exclusion cover Medicare tax?
No, and this is the single most expensive misunderstanding in the area. The exclusion removes foreign salary from your income tax calculation. It leaves self-employment tax untouched, so a freelancer can owe nothing in income tax and still face a bill for the social security element.
The IRS says so directly. You count all your self-employment income when you work out net earnings, even where the exclusion removed it from income tax. The threshold is only $400 of net earnings.
If you are weighing the exclusion against the credit for other reasons, our comparison of the exclusion and the foreign tax credit sets out the trade-off.
Why self-employment is where people get caught
Employees rarely stumble here. Their British employer deducts National Insurance, the payslip records it, and the agreement does its job quietly. Freelancers have no such paper trail unless they build one.
A consultant invoices clients from a flat in Bristol. She pays Class 2 and Class 4 National Insurance through Self Assessment. That is the UK system taking the earnings. Without a certificate, however, her US return shows nothing of it, and the self-employment tax line waits.
In our practice this turns up most often in the second or third year abroad, once someone reads the form properly. The fix is administrative rather than clever, and it is described further down.
What about the Additional Medicare tax?
The 0.9% Additional Medicare tax is a separate charge on wages, other compensation and self-employment income above set thresholds. The IRS notes that it does not apply to investment income, and that it sits alongside rather than inside the net investment income tax. Two charges, two bases, no overlap.
For someone abroad, the practical point follows from the last section. If your earnings belong to the UK system under the agreement, the Additional Medicare tax has nothing to attach to either.
Is the net investment income tax a Medicare tax?
People call the 3.8% net investment income tax a Medicare surtax, which is misleading. It applies to investment income above the thresholds, not to earnings, and it is charged on your income tax return. That matters abroad because foreign tax credits do not offset it.
So a US citizen in Britain with dividends and gains can pay UK tax on that income, claim a credit against the US income tax, and still owe the 3.8% charge on top. Unlike the payroll charges, no social security agreement helps here.
Can you deduct what you spend on healthcare here?
Sometimes, though less often than people hope. The US allows medical costs as an itemised deduction only to the extent that they exceed 7.5% of adjusted gross income, and only if you itemise at all. Most people abroad take the standard deduction, which ends the question.
There is a further wrinkle. If you exclude your salary under the foreign earned income exclusion, deductions that relate to the excluded income are cut back in proportion. Claiming a deduction against income you told the IRS to ignore is not a position that survives review.
The immigration health surcharge sits in the same uncertain territory. We do not treat it as an insurance premium without looking at the individual facts, because the IRS has published nothing that names it.
What about medical cover from your employer?
Private medical insurance from a British employer counts as a reportable benefit here. A narrow list of exemptions applies. Treatment abroad for an employee working overseas can qualify. So can one health screening a year, eye tests for screen work and flu jabs.
The US side reads differently. Employer contributions to an accident or health plan are generally excluded from wages under the fringe benefit rules. So a benefit that increases your UK tax may not increase your US income at all, which affects how much credit you have to work with.
Our piece on National Insurance for Americans covers the contributions side of the same payslip.
Claiming the agreement, step by step
The administrative route is short, and it is worth doing before the return rather than after.
- Work out which country's system should hold your earnings: where the work happens and who employs you are the first two questions.
- If the answer is Britain, apply to HMRC for a certificate of coverage confirming you pay National Insurance on those earnings.
- Keep the certificate with your tax papers. It is the document that supports leaving self-employment tax off the return.
- File the US return showing the income and, where the agreement applies, no self-employment tax on the same earnings.
- Check the position again whenever your work changes country, employer or legal form, because the answer can change with it.
An illustrative example
Take an illustrative case. A US citizen moves to Manchester and works as a self-employed designer, billing UK clients about £70,000 a year. She pays UK income tax and National Insurance through Self Assessment, and her US income tax comes to nothing once the exclusion is applied.
Without a certificate of coverage, her US return still shows self-employment tax on the full net profit. With the certificate, that line disappears. The figures are illustrative, though the shape of the outcome is the one we see repeatedly: the income tax was never the problem.
What the tax does not buy you abroad
Paying into a system and drawing from it are different questions, and they are handled by different agencies. Whether Medicare pays for treatment outside the United States, and what happens to enrolment while you are away, is a benefits matter for the Social Security Administration.
We do not advise on it, and we would rather say so than guess. Ask the agency directly before you rely on an answer, because the cost of a wrong assumption here is a health bill rather than a tax one.
Common mistakes we see
Three patterns come up again and again. First, treating the income tax treaty as though it covered social security charges, when it does not. Second, assuming the foreign earned income exclusion wipes out self-employment tax. Third, leaving the certificate of coverage until after the return is filed.
The fourth is quieter. People who incorporate a UK company change their own position without noticing, because a salary from that company is employment rather than self-employment. That is worth advice before the change, not after.
What paperwork should you keep?
Keep three things: your payslips and P60, the certificate of coverage once you hold one, and your Self Assessment returns. The payslips record the National Insurance you actually paid. Together they answer the only question that matters, which is simply which system took these earnings.
Store them by tax year, not by employer. The two countries run different years, so a pile sorted by job turns into guesswork later.
Our clients who keep this tidy spend far less on the eventual return. The ones who do not usually pay us to rebuild a year from bank statements.
What happens when you move back?
The position flips. Work performed in the United States belongs to the US system again, so the payroll charges resume from the first pay run. National Insurance stops when the UK work stops. Nothing carries over, and nothing needs unwinding, though the year of the move splits into two halves.
Plan the split before you fly. A mid-year move leaves one country's system holding part of the year and the other holding the rest.
Self-employed people should also cancel the certificate of coverage. It describes a working pattern that no longer exists.
How US UK Tax Hub helps with Medicare tax questions
We start by establishing which system owns your earnings, then make the paperwork match. That usually means a certificate of coverage, a consistent Self Assessment position and a US return that lines up with both. Our treaty relief service covers the wider cross-border position, including the parts the social security agreement does not reach.
Where a charge is genuinely due, we say so early. Where it is not, we make sure the file can prove it. You can ask us about your own position before the next filing season starts.
