Getting a Social Security number as an adult who has never lived in America

It is your taxpayer identification number as a citizen. It goes on your federal return, on the forms your bank asks you to complete, and on any benefit claim you may make one day.

It does not create any new obligation. The duty to file exists already, as the IRS page for citizens abroad explains.

It simply gives the system a way to match your filings to you.

No. The IRS says you cannot hold both numbers, and it lists anyone eligible for one among the people who do not need an ITIN. Citizens are eligible for one, so that is the only route open to you.

An ITIN exists for people who cannot get one.

The IRS page on the ITIN sets out who qualifies for which number.

Because the IRS says every return filed under the Streamlined procedures must carry a valid taxpayer number, and for a citizen that means a Social Security number. Without one, the IRS will not process the return under the procedure.

So the number is the first step in any catch-up, not the last.

The IRS Streamlined page states the requirement.

British banks must report a US tax number for accounts they treat as held by Americans. HMRC guidance lets them report a date of birth instead for a limited period, but only while they keep requesting the number every year.

That explains the annual letters.

The rules sit in HMRC's manual on reporting a US TIN.

The Federal Benefits Unit at the US Embassy in London deals with these applications from people living in the UK. Anyone over 12 must attend a short interview, held in London or at a designated US military installation.

Children under 12 can usually apply by post.

You request the interview through the embassy's contact form, giving a few working days' notice.

Work visa holders follow a different path. They apply after arriving in the United States, at a local office.

Originals only, because the embassy refuses photocopies. You need proof of birth, such as a US birth certificate or a Consular Report of Birth Abroad, proof of citizenship, and proof of identity, usually a current signed passport.

Bring photocopies as well, because staff keep copies and return the originals.

Missing one document can mean a second interview.

Because a citizen born in America would normally have received a number long ago. So an adult born in the US must produce documents covering a significant part of the time spent outside America, which explains why nobody issued a number.

School records, employment records and medical records all help.

In our practice this is the document set people find hardest to assemble, so start gathering it early.

Form SS-5-FS, the version of the card application used outside the United States. Answer every question, write legibly, and make sure the details match your supporting documents exactly, including any middle names.

Blank answers are the most common reason for delay.

Complete it before the interview rather than at the counter.

It is short and administrative. An officer checks your documents, compares them with the form, and confirms the citizenship evidence supports the application. Then the officer keeps copies and hands back the originals.

Questions usually concern where you have lived and why you never had a number.

Answer plainly. Nobody is testing you, and the interview is not about tax.

Roughly eight to ten weeks for processing, according to the embassy, and that follows the wait for an interview slot. Posted documents come back within a few days of arriving.

So allow two to three months from start to finish.

Plan any deadline around that, especially a bank's.

Holiday periods can stretch it further, so avoid starting in late November if a January deadline matters.

Yes. Social Security posts the card to the address on your application, which can be in the UK. Keep it safe, because a replacement takes the same route and the same wait.

Write the number down separately as well.

In practice the number matters far more than the card itself, since forms ask for the digits rather than the plastic.

Store a copy of the card with your tax records. You will need the digits again every single year.

Then you apply for a replacement card rather than a new number. Social Security stopped issuing printouts or verifications of numbers in 2014, so a replacement card is the way to prove the number you hold.

This works even if you cannot remember the number itself.

Many adults discover a parent applied for them as a baby.

Ask a parent first. An old tax return, a savings bond or a childhood account statement may show a Social Security number issued years ago.

Then your proof of citizenship is usually a Consular Report of Birth Abroad, or a passport issued on the strength of one. Without either, citizenship may need confirming before an SSN can follow.

That confirmation is a question of your parent's history, not yours.

Our note on American children born abroad sets out how citizenship passes.

Tell your bank you have applied, and keep proof of the application in case it asks. Meanwhile, prepare the returns and FBARs in full, leaving the number to add at the very end, so that filing can happen the week the card arrives.

You file the FBAR separately through FinCEN's system, so gather six years of balances now.

You gain nothing by waiting to start the rest of the work.

Indirectly, yes. American credits for children generally require the child to hold an SSN, so a family catching up often applies for everyone at once. That way the credit is available from the first return you file rather than a year later.

Children under 12 can apply by post, which is simpler.

We cover the credit in the child tax credit abroad.

Then bring evidence linking the names, such as a marriage certificate or deed poll. Social Security uses the name on your current identity document, so the link between your birth name and your current name must be clear.

Mismatched names are a common reason for a second appointment.

Your returns should then use exactly the name on the card, because the IRS matches the two.

No. Holding a number does not make you pay American social security tax, and it does not start any benefit. Those depend on where you work and what records you build, not on the number itself.

Employees on a British payroll usually pay National Insurance only, under the totalisation agreement.

The number simply lets the agencies identify you when you file.

Then settle that question first, because the application depends on it. Someone born in America is usually a citizen, but someone born abroad to an American parent is a citizen only if the parent met the residence conditions at the time.

A Consular Report of Birth Abroad or a US passport settles it.

Without either, take advice before applying, since the embassy will ask for proof you may not have.

This order avoids a second trip to London.

Take a Bristol engineer born in Denver who left at two. Her bank has written twice asking for a US tax number, and she has decided to catch up under the Streamlined route.

She books an interview, brings her US birth certificate, British passport and school records, and receives her card nine weeks later.

Her returns were ready by then, so she filed the week the card arrived. This example is illustrative, not advice.

Her bank accepted proof of the application in the meantime, and the account stayed open.

Often it makes sense. A parent catching up on their own returns usually wants numbers for any American children too, since credits and the children's own future filings will need them, and gathering one set of family documents is easier than two.

Children under 12 can apply by post, while adults and older children attend in person.

Booking the adult interviews on the same day saves a second journey to London.

On every American return, on the W-9 your bank may ask you to sign, and on any correspondence with the IRS. Banks use a Form W-9 to record a US person's taxpayer number for their FATCA files.

Give it only to institutions that genuinely need it.

The IRS page for Form W-9 explains the form.

First, applying for an ITIN because it looks quicker. It is not available to citizens.

Second, sending photocopies.

Third, leaving the application until you have finished the returns, which adds months to the whole process.

Fourth, ignoring the bank while waiting, rather than telling it an application is in hand.

Fifth, filling in the form with a different name order from the passport. Small mismatches cause long delays.

We plan the Social Security number application alongside your US federal return, so neither waits for the other. We also check the citizenship question first where it is unclear.

For people catching up, we fold the timing into the Streamlined package explained in our Streamlined guide.

This article is general information, not personal tax advice. Talk to us before your interview.