Self-Employed Abroad: US Self-Employment Tax and How to Escape It

The $400 trigger

Self-employment puts you on the IRS's radar at a remarkably low level: net earnings of $400 or more from self-employment create a US filing requirement by themselves, whatever your other circumstances. A UK-based American doing occasional consulting, selling online or freelancing between jobs is inside the system at the first few hundred dollars of profit.

The business itself is reported on Schedule C — income and expenses, converted to dollars — with the net profit flowing into the return like any other income. So far, ordinary. The trap is in the next layer.

Self-employment tax: the charge nothing else removes

Alongside income tax, US law levies self-employment tax — the self-employed person's version of Social Security and Medicare contributions — at 15.3 percent of most net self-employment earnings (12.4 percent Social Security up to an annually adjusted wage base, plus 2.9 percent Medicare with no cap).

Here is the part that surprises almost every expat freelancer: neither the foreign earned income exclusion nor the foreign tax credit reduces it. The FEIE excludes income from income tax only — excluded profit is still subject to SE tax. Foreign tax credits offset income tax only — UK income tax paid cannot be credited against a social security charge. A freelancer whose income tax bill is zero can still owe the full 15.3 percent to the US, while simultaneously paying UK National Insurance on the same profits. Double social security, with no relief from any of the usual machinery.

The relief lives somewhere else entirely.

The totalization agreement: one system, not two

The United States and the United Kingdom have a totalization agreement — a social security treaty, separate from the income tax treaty — whose purpose is exactly this problem: making sure a worker contributes to one country's system at a time, and helping combined contribution records qualify for benefits later.

Under the agreement, a self-employed person is generally assigned to the social security system of the country where they reside. A US citizen living and freelancing in the UK therefore normally belongs to the UK system: National Insurance is due, and US self-employment tax is not.

The exemption is claimed with evidence, not assumed. The standard proof is a certificate of coverage — for a UK-resident freelancer, obtained from HMRC — confirming you are covered by UK National Insurance under the agreement. With that in hand, the US return reports the self-employment income but takes the exemption from SE tax, citing the agreement. Keep the certificate; the IRS can ask for it.

There is a real choice buried here for some people: exempt from US SE tax means not accruing US Social Security credits for those years. For most UK-resident freelancers, paying one system — the one where they live — remains the sensible default, but anyone close to a US benefit threshold should look before leaping.

Estimated taxes: paying as you go

The US expects tax to arrive during the year, not just at filing. Self-employed taxpayers who will owe US tax — because the totalization exemption does not apply, because investment income creates liability, or because credits will not cover everything — generally make quarterly estimated payments, with interest-based penalties for underpayment. Whether you need them is a bottom-line question: many UK-based freelancers, fully covered by the totalization agreement and foreign tax credits, owe nothing during the year — while others, particularly those with US-source income on the side, need the quarterly discipline.

The UK, meanwhile, runs its own version through Self Assessment payments on account. The two calendars do not align, which is an argument for having both returns prepared by people looking at the same numbers.

Beyond the sole trader

Everything above assumes a simple unincorporated business. Add a structure — a UK limited company, a US LLC used from the UK, VAT registration, employees — and the cross-border analysis changes materially, sometimes in expensive ways. Our guide for freelancers and consultants working across the US and UK picks up the structuring questions; the message here is narrower and worth keeping: report the business from the first $400, and never pay social security twice without checking the agreement first.