The certificate of coverage: ending, and refunding, US self-employment tax from Britain

Figures relate to tax year 2025 (US) · 2025-26 (UK)

HMRC will issue a one-page document that can end years of US self-employment tax. A certificate of coverage confirms that British National Insurance covers you, and the IRS accepts it in place of the 15.3% American charge. Attached to amended returns, it can also bring back tax already paid.

Few American freelancers in Britain know the document exists. So this guide covers how to obtain it, how to attach it, how far back a refund can reach, and when the certificate stops protecting you.

Key takeaways

• HMRC issues the certificate, and the IRS accepts it as proof that British National Insurance covers you.
• Attached to a US return, it removes the 15.3% self-employment tax on British self-employed profit.
• A statement that you have applied is enough if the certificate has not yet arrived.
• Amended returns can recover self-employment tax paid in earlier years, within the refund window.
• The certificate runs for a set period and ends if you move or change how you work.
• Neither the earned income exclusion nor foreign tax credits achieve the same result.

What is a certificate of coverage?

It is a document from one country's social security authority confirming that you pay into its system. Under the agreement between Britain and America, that confirmation exempts you from the other country's social security charge. For a self-employed American living here, HMRC issues it and the IRS accepts it.

Think of it as the proof behind a treaty right. The right exists under the agreement, but without the document the IRS has no way to see it.

How do you get a certificate of coverage?

You apply to HMRC's National Insurance office, which confirms that you pay into the British system as a self-employed resident. The request needs your National Insurance number, your US Social Security number, your address and details of your self-employment. Processing can take several weeks.

Apply before you file if you can. Where the certificate has not arrived by the deadline, the IRS accepts a statement explaining that you have applied, and the certificate follows later.

Keep the certificate with your permanent tax papers. It usually covers a stated period, and you will need a fresh one when that period ends or your circumstances change.

How to claim the exemption on your US return

The exemption is claimed, not assumed. Leaving Schedule SE blank without the supporting document invites a notice charging the full amount, plus interest from the original due date.

1. Confirm you live in Britain and work for yourself rather than as an employee.
2. Apply to HMRC for a certificate of coverage covering the relevant years.
3. Complete your US return with self-employment income reported as normal.
4. Omit the self-employment tax and attach a copy of the certificate.
5. Where the certificate is still pending, attach a statement saying you have applied.
6. Keep paying Class 4 National Insurance through your Self Assessment return.
7. Diarise the certificate's end date so the next one arrives in time.

Can you recover self-employment tax already paid?

Often, yes. Where the certificate covers earlier years, amended returns can remove the self-employment tax for those years and produce a refund. The normal refund window of roughly three years from filing limits how far back that works.

This is one of the few areas where fixing old returns puts money back in your pocket. Our guide to amending a US tax return covers the mechanics of reopening a filed year.

In our practice the refunds are frequently larger than clients expect. Three years of self-employment tax on a steady freelance income can easily run to tens of thousands of dollars.

A worked example

The figures below are illustrative. Take an example: an American designer in Bristol earns $90,000 of freelance profit each year and has paid US self-employment tax for three years without a certificate.

Each year the American charge ran to roughly $12,700. Over three years that is about $38,000, paid on top of British National Insurance on the same profit.

With the certificate in place, the designer amends all three returns and removes the charge. The refund arrives with interest, and future returns carry the certificate from the start.

The designer also keeps paying Class 4 in Britain. At 2025-26 rates that comes to under £3,000 a year. So the saving is the full American charge, not a swap of one bill for another.

How long does the certificate last?

It covers a stated period, not a lifetime. Most run for a set number of years or until your circumstances change. So check the dates each spring. Then apply again before the old one ends.

Also watch for changes that end cover early. A move abroad, a switch to employment, or a new business structure can all change the answer.

What if you are both employed and self-employed?

Then each income stream follows its own rule. A British salary sits in the British system through Class 1 contributions. Side income from freelance work also sits there if you live in Britain. So the American charge falls away on both, provided the paperwork shows it.

Mixed years are common in the first year of a move. Still, the rule stays the same. Residence decides the self-employed part, and the employment rules decide the rest.

What happens if you move back to America?

Then the assignment flips. Once you live in America and work for yourself there, American self-employment tax applies and British contributions stop being compulsory. So British coverage ends from the date your residence changes. Plan the switch in the year of the move.

Voluntary British contributions can still make sense afterwards. They protect a State Pension record at low cost. Also, they sit outside the assignment rules entirely.

What if you run a UK limited company?

Then the answer changes, because you become an employee of your own company. Salary from the company falls under British Class 1 National Insurance, and the agreement assigns a locally employed worker to the British system too. Dividends are not social security income in either country.

The American side can still differ where the company is treated as a partnership or disregarded entity for US purposes. That classification decides whether profit counts as self-employment income, so check it before assuming the company solves the problem.

Ask before you incorporate. The structure you choose on day one tends to stick for years.

Why does the US charge self-employment tax abroad?

Because citizenship reaches social security as well as income tax. An American with self-employed profit owes self-employment tax wherever the work happens. Excluding the income from income tax does nothing to the social security charge, which runs on a separate schedule.

The rate is 12.4% for Social Security up to an annual wage base, plus 2.9% for Medicare with no ceiling. For 2025 the wage base stood at $176,100. An additional Medicare charge of 0.9% applies above higher income thresholds.

So a freelancer with $80,000 of profit can face over $11,000 of self-employment tax. That is before a single dollar of income tax, and before Britain has charged anything.

What Britain charges on the same profit

Class 4 National Insurance runs at 6% on profits between £12,570 and £50,270 for 2025-26, and 2% above that. Class 2 contributions stopped being compulsory from April 2024, though you can still pay them voluntarily. So for a typical freelancer the British bill is well under half the American one.

The agreement does not let you choose the cheaper system. It assigns you to one of them, and for a self-employed person living in Britain that system is the British one.

How the agreement assigns you

For self-employed people the rule is residence. If you live in Britain and work for yourself, British National Insurance covers you, and American self-employment tax does not apply. According to IRS guidance on totalization agreements, the certificate is how you demonstrate that coverage.

Employees follow a different rule. A worker sent abroad by an employer for five years or less usually stays in the home system, while a local hire joins the local one. Our guide to voluntary National Insurance covers how contribution records build up on each side.

What about your US Social Security record?

Paying into the British system instead of the American one stops new US credits building. But the agreement lets each country count periods in the other toward eligibility for benefits. A shorter American record can still qualify for a partial American pension once British periods are added.

Benefits are then calculated separately by each country. Our guide to the State Pension and Social Security explains how the two records combine in practice.

Is this worth doing for a small side business?

Usually, yes. Self-employment tax applies once net earnings reach $400 a year. So even a modest side income can carry a charge. But the application costs nothing except time, and the saving repeats every year.

Even at $10,000 of profit the charge runs to about $1,400 a year. That buys a great deal of paperwork.

What records should you keep?

Keep the certificate, the application, and each Self Assessment return showing Class 4 paid. Keep the US returns with their attached copies as well. Together they prove both halves of the position if either authority asks.

Store them for as long as the certificate runs, plus the usual period after. In our experience a missing copy is the most common reason a notice drags on for months.

Scan everything once and file it by year. Then the next application, or the next amendment, takes minutes rather than days.

Mistakes and penalties we see with self-employment tax

• Assuming the foreign earned income exclusion removes self-employment tax, which it never does.
• Trying to offset self-employment tax with foreign tax credits for British income tax.
• Leaving Schedule SE blank without attaching a certificate or a statement.
• Letting a certificate lapse and carrying on as if it still applied.
• Missing the refund window for earlier years that the certificate would have covered.
• Stopping Class 4 payments in Britain on the mistaken view that the agreement exempts both sides.

The penalties follow the unpaid tax. A notice charging self-employment tax carries interest from the original due date, and late payment penalties can follow if the notice sits unanswered.

How US UK Tax Accountants helps

We apply for the certificate, attach it correctly, and amend earlier years where a refund is available. For most freelancers this is the single most valuable fix on the return. If you work for yourself in Britain and pay American self-employment tax, get in touch and we will check your last three years alongside your US federal returns.

Last reviewed 21 September 2026. This article is general information and not personal tax advice. Rates, wage bases and thresholds change each year, so check the figures for your own filing year.