An adult US citizen living in the UK who has never had a Social Security number applies for one on Form SS-5-FS through the Federal Benefits Unit at the US Embassy in London, and attends an interview in person. The number has to come before the tax work. A citizen cannot use an ITIN in its place, and the IRS requires a valid taxpayer identification number on every return in a streamlined submission (opens the official IRS page in a new tab).
This post is for people who have learned in adult life that they are American, often after a bank letter, and now need a number before they can file anything. It goes further than the short section in our guide for people who are behind on US taxes in the UK: who gets which number, how the application runs from the UK, what evidence is asked for, how long to allow, and what the wait means for the timing of a catch-up filing.
Does a US citizen need a Social Security number or an ITIN?
A US citizen needs a Social Security number. The IRS issues an individual taxpayer identification number (opens the official IRS page in a new tab) only to people who have a federal tax purpose and are not eligible for a Social Security number. A citizen is always eligible, so the ITIN is closed to them however long they have lived abroad.
The confusion is understandable. Both numbers identify a taxpayer on a US return, and the ITIN is the one applied for through the tax system, on Form W-7 (opens the official IRS page in a new tab). The IRS guidance says that anyone eligible for a Social Security number does not need an ITIN, and that a person cannot hold both. Our page on Form W-7 explains who that form is for, which is usually a non-US spouse or dependant and not the citizen.
The number is needed because the IRS treats US citizens abroad (opens the official IRS page in a new tab) as subject to the same filing rules as those at home. A citizen whose worldwide income is above the filing threshold for their status files Form 1040 each year, and the return asks for the filer's number. The late returns in a catch-up submission are no different.
- US citizen, wherever born or living: Social Security number
- Green card holder: Social Security number
- Non-US spouse or dependant who must appear on a US return: usually an ITIN
- Someone who has already given up US citizenship: see the separate relief described below
How do you apply for a first Social Security number from the UK?
You complete Form SS-5-FS, the version of the Social Security card application used outside the United States, and apply through the Federal Benefits Unit at the US Embassy in London. The Social Security Administration has no offices abroad, and its regulations require an in-person interview for anyone aged twelve or older applying for an original number.
The Social Security Administration says on its international pages that embassies and consulates assist its customers who live outside the United States. The London unit covers the whole of the UK. Applications for young children, replacement cards and name changes are handled by post. A first number for an adult is not, because of the interview rule, so the unit arranges an appointment.
The embassy asks for appointment requests in writing, through its contact form or by email, and asks applicants to say whether they were born in the United States or abroad. It has warned that bookings made through third-party scheduling sites are not recognised and will not get a visitor into the building. It has also announced the end of its incoming telephone service, so written contact is the only route. Interviews for UK residents are held at the unit in London or at a designated US military installation.
Two points save a wasted journey. Every question on the form has to be answered legibly. And the unit deals with Social Security matters only: its own page says it cannot answer questions about the IRS, passports or visas, so tax questions belong with whoever prepares the returns.
What documents does the Federal Benefits Unit ask for?
The unit asks for original documents proving birth, US citizenship and identity, and, for anyone born in the United States, proof of having lived outside it. Photocopies are not accepted as evidence. The regulations allow originals or copies certified by the office that holds the original record.
One document can serve more than one purpose. A US birth certificate is listed as proof of both birth and citizenship. A person born abroad to an American parent relies instead on a Consular Report of Birth Abroad, a certificate of naturalisation or citizenship, or a US passport. Someone who holds none of these has a nationality question to settle before a number can be issued, a point covered in our post on accidental Americans in the UK.
For identity, the embassy lists a current, signed passport, which may be American or foreign, so a British passport is acceptable for this purpose. Where the name on the passport differs from the name at birth, evidence of the change is needed too. The embassy suggests bringing photocopies along with the originals, so that the copies can be kept and the originals handed back at the interview.
- The completed Form SS-5-FS
- Proof of birth: a US birth certificate, a Consular Report of Birth Abroad or another birth certificate
- Proof of citizenship: a US birth certificate, consular report, naturalisation or citizenship certificate, or US passport
- Proof of identity: a current, signed US or foreign passport
- If born in the United States: Form SSA-L706, which lets the birth record be verified with its custodian
- If born in the United States: documents showing residence abroad since leaving
Why do adults have to prove they lived outside the United States?
Because an adult born in the United States is expected to have a number already. The embassy describes it as very rare for someone born there never to have been assigned one, and asks for documents showing absence from the country as the explanation. The usual case is a child who left when very young.
The evidence should run from the date of departure to the present. The embassy says proof for every single year is not required, but the documents together must show foreign residence across the period, and it states that an application will not be accepted where that evidence is insufficient. Its suggested documents include school reports or a letter confirming dates of attendance, current and cancelled passports, employment records, medical records and proof of registration with a doctor.
A worked example: a secondary school teacher in Bristol was born in Texas while her British parents were working there and came to England as a baby. She has never held a US passport. She takes her Texas birth certificate, which covers birth and citizenship, and her British passport for identity. She completes Form SSA-L706. For residence she gathers primary and secondary school records, her university transcript, her employment history, her old British passports and a letter from her GP surgery showing registration since infancy.
How long does a Social Security number take to arrive?
Allow months, and do not plan a filing date around a shorter period. The embassy publishes an approximate processing time, counted in weeks, for the applications it handles by post, and says that a replacement card cannot be expedited. It gives no separate figure for adult first-time applications, which also depend on getting an interview.
The appointment is the first variable. The embassy says interview slots are limited, and its pages give different notice periods for requesting one, so ask early and follow whatever the reply says. The second variable is evidence. An applicant who arrives without every required document may be asked to come back for a second interview, and the verification of a US birth record with the state that holds it is outside the applicant's control.
There is no interim proof. The Social Security Administration stopped issuing printouts or verifications of a number some years ago, and the embassy confirms that the card itself is the only proof. We do not quote a turnaround for this stage, because it is not ours to control. The practical answer is to apply as soon as US status is confirmed and to use the waiting time on the tax records.
What does waiting for a number mean for a streamlined submission?
It means the submission cannot be posted until the number arrives. The IRS says all returns submitted under the streamlined procedures must carry a valid taxpayer identification number, which for a citizen is a Social Security number. Its allowance for filing with a pending ITIN application covers only people who are not eligible for a Social Security number.
The waiting time can still be used. The Streamlined Foreign Offshore Procedures (opens the official IRS page in a new tab) ask for three years of returns and six years of FBARs, counted back from the most recent year whose due date has passed. Records can be gathered, returns drafted and the narrative written while the application is in progress. Because the look-back moves with the calendar, a long wait can bring a new year into the package, so the years are confirmed again once the number is issued. The FBAR covers every year in which foreign accounts together exceeded $10,000, and FinCEN's guidance (opens the official FinCEN page in a new tab) is the place to check how it is filed.
The wait does not change the terms of either route. The Foreign route carries no penalty beyond tax and interest for a person who qualifies, and the Domestic route (opens the official IRS page in a new tab) charges a 5% miscellaneous offshore penalty. Both require non-wilful conduct, certified in writing, and neither is available once the IRS has opened an examination. A prompt application, with the dated emails and appointment confirmation kept on file, helps show that the taxpayer acted on learning of the duty, which matters when writing the Form 14653 certification.
One group does not need a number at all. The relief procedures for certain former citizens (opens the official IRS page in a new tab) say that a person who has already relinquished citizenship need not obtain a Social Security number merely to use them. Everyone else applies first. Our IRS streamlined filing service prepares the package in parallel with the application, and individual tax returns covers the annual filing that follows. The full sequence is in our guide for people who are behind on US taxes in the UK.
- Confirm US citizenship with documents before anything else
- Request the interview and assemble the residence evidence
- Gather account and income records while the application is processed
- Answer any bank self-certification truthfully, saying a number has been applied for
- Post the streamlined package once the card arrives
General information, not advice. The right answer depends on your circumstances and the tax year concerned.
