Often yes. The US expat filing requirement is set by gross income, counted worldwide and before the foreign earned income exclusion or the foreign tax credit, measured against a threshold for your filing status. For a single filer under 65 the threshold for tax year 2025 is $15,750, and for married filing separately it is only $5. A modest UK salary can therefore create a duty to file Form 1040 (opens the official IRS page in a new tab) even where no US tax will be due.
This post is for US citizens and green card holders in Britain on a part-time wage, a single small salary, savings income or a pension, who want to know whether the US expects a return at all. It goes deeper on one question than our guide to US and UK tax returns for Americans in the UK. It covers the thresholds, what counts as gross income for a UK resident, the self-employment rule, why filing below the threshold can still pay, and why the FBAR is a separate question.
What income level triggers a US tax return for an American abroad
The threshold depends on filing status and age. For tax year 2025, a filer under 65 must file once gross income reaches $15,750 if single, $31,500 if married filing jointly, and $5 if married filing separately, at any age. Head of household and older filers have their own figures in the IRS charts.
Publication 501 (opens the official IRS page in a new tab) sets out the full table, and the Form 1040 instructions repeat it as Chart A. The instructions say the rules apply to all US citizens, wherever they live, and to resident aliens. A UK address changes where the return goes and the due date, not whether one is needed. The guidance on US citizens and resident aliens abroad (opens the official IRS page in a new tab) says the same.
Filers aged 65 or over at the end of the year have a slightly higher threshold, and so do couples where one or both spouses are 65 or older. The single and joint figures quoted here are the under-65 amounts. Someone close to that age, or with a spouse who is, should read the chart for their own row before concluding that no return is due.
- Single, under 65: $15,750 of gross income
- Married filing jointly, both under 65: $31,500
- Married filing separately, any age: $5
- Head of household and filers aged 65 or over: the higher figures in Chart A
- Net earnings from self-employment above a low fixed amount: a return whatever the gross income
Why married filing separately catches almost everyone
A US citizen married to a British spouse who is not a US person usually files as married filing separately. That status has a gross income threshold of $5, so a few pounds of UK bank interest is enough to require a return. It is the most common reason a low earner in Britain still has to file.
A joint return with a non-US spouse is possible only by election, which brings the spouse's worldwide income into the US return. Many families decide against it for that reason. Head of household status can sometimes be used where a qualifying child lives with the US parent, and it has a higher threshold, but it has its own conditions. Our post on which US filing status applies when married to a Brit works through the choice.
The Form 1040 instructions add one more point. A married person who did not live with their spouse at the end of the year must file once gross income reaches the married filing separately figure, regardless of age. Separated couples who have not divorced should check their status before relying on the single threshold.
What counts as gross income for a US citizen living in the UK
Gross income means all income received as money, goods, property or services that is not exempt from tax, including income from outside the United States. For the filing test it includes salary you could exclude under the foreign earned income exclusion. It is counted before deductions, credits and the exclusion, and losses do not reduce it.
Publication 54 (opens the official IRS page in a new tab) states the point about exclusions directly: for deciding whether you must file, gross income includes any amount you can exclude as foreign earned income or as a foreign housing amount. So a UK salary that will end up fully excluded on Form 2555, or fully covered by UK tax through the credit on Form 1116, still counts in full towards the threshold.
UK tax-free status does not help either. Interest inside a cash ISA and Premium Bond prizes are free of UK tax, yet the US has no matching exemption, so both count. Gains count, but losses on other sales do not reduce them. Business income counts at the gross income figure on Schedule C, not the net profit. Social security benefits are left out of the test unless you file separately and lived with your spouse at any time in the year.
- UK salary and bonuses, before PAYE and before any exclusion
- Interest from UK bank accounts, including cash ISAs
- Dividends from UK shares, funds and investment ISAs
- Rental income from a UK or US property
- Gains on sales of shares, funds or property, with losses left out
- Gross business income from freelance or sole trader work
Does self-employment change the US expat filing requirement
Yes. A US citizen with net earnings from self-employment above a low fixed amount set in the IRS instructions must file even when gross income is below the threshold for their filing status. The rule exists because self-employment tax is worked out on the return, separately from income tax.
Publication 54 and Table 3 of Publication 501 both state this rule. For a US citizen in Britain the self-employment tax position is shaped by the totalization agreement (opens the official SSA page in a new tab) between the two countries, which generally assigns social security coverage to one country only. A sole trader in the UK paying UK National Insurance is often exempt from US self-employment tax, but the exemption is claimed with a certificate of coverage, not assumed.
That makes freelance income in the UK a common trigger for a return that nobody expected. A short side project, a few months of consulting or a small online business can pass the net earnings figure on its own. Our post on self-employment in the UK as a US citizen covers the social security side in more detail.
Why file a US return when you are under the threshold
Filing can still be worth it below the threshold. A return is the only way to claim a refundable credit such as the additional child tax credit, and the IRS lists that credit as a reason to file even when not required. A filed return also starts the time limit for the IRS to assess tax for that year.
The child tax credit (opens the official IRS page in a new tab) has a refundable part, worked out on Schedule 8812 (opens the official IRS page in a new tab) from earned income. The 2025 Schedule 8812 instructions say a filer who claims the exclusion on Form 2555 cannot claim the additional child tax credit, and each qualifying child needs a valid social security number. A low-earning parent who uses the foreign tax credit instead may receive a payment. Our post on the child tax credit for American families in Britain explains the trade-off.
The time limit point is less obvious. IRS guidance on recordkeeping says there is generally no period of limitations to assess tax for a year in which no valid return was filed. A return showing nil tax closes that door after the normal period. It also creates a record of foreign tax credit carryovers and of compliance, which matters later for Streamlined eligibility or a renunciation.
- Claiming the refundable part of the child tax credit
- Starting the IRS time limit for assessing that year
- Recording unused UK tax as a foreign tax credit carryover
- Building the five-year compliance record that renunciation requires
Is the FBAR tied to the income threshold
No. The FBAR has its own test and has nothing to do with income. It is required once the combined maximum value of all your foreign financial accounts exceeds $10,000 at any time in the year. A US person with almost no income but some savings in UK accounts can owe an FBAR and no tax return.
The FBAR (opens the official FinCEN page in a new tab) is filed electronically with FinCEN, not with the IRS and not attached to Form 1040. Its due date is 15 April, extended automatically to 15 October. The threshold is an aggregate across every account, so a current account, a savings account and a cash ISA that each look small can pass it together. Accounts you can sign on, such as an employer's account or a parent's, count as well as accounts you own.
The reverse also happens. A low earner below the FBAR threshold may still have a tax return to file because of the married filing separately rule. Our foreign income and FBAR service handles both, and the FBAR form page sets out who files.
How the rules work for a low earner in Bristol
Take a US citizen working part-time in Bristol, married to a British spouse, with a small UK salary, a savings account and a cash ISA. Her salary is well below the single threshold, and she assumes that no US return is needed because UK tax is taken through PAYE.
Her filing status is likely to be married filing separately, so the threshold is $5 and her salary alone means she must file. Her ISA interest counts as gross income too. The UK tax on her salary is likely to remove most or all of any US tax through the credit, but that relief is claimed on the return. If her combined account balances exceed $10,000 at any point, she also files an FBAR.
If she has missed earlier years, the question becomes how to catch up, which our post on being behind on US taxes but owing nothing covers. For the current year, she files by 15 June under the automatic extension for filers abroad. Our individual tax returns service prepares returns of this kind, and the guide for Americans in the UK sets out the full yearly cycle.
General information, not advice. The right answer depends on your circumstances and the tax year concerned.
