Figures relate to tax year 2025-26 (UK) · 2025 (US)
Sooner or later a British person dealing with American tax hits a wall. A form wants a taxpayer number. You have no Social Security number. Nothing moves until you get one.
The answer is an ITIN. America issues it to people who must deal with its tax system but cannot get a Social Security number.
The snag is proving who you are. The default route asks you to post your real passport to Texas and wait. That is why so many an ITIN application stalls before it starts.
Key takeaways
- An ITIN is for people who cannot get a Social Security number.
- It is for tax purposes only and confers no immigration status.
- The application is made on Form W-7.
- It usually has to accompany a tax return rather than stand alone.
- Original passports can be sent, but there are safer options.
- A certifying acceptance agent can verify documents for you.
- Numbers lapse if unused on a return for three consecutive years.
What is an ITIN?
A nine digit number for people who owe an American filing duty but cannot get a Social Security number. According to IRS guidance, it exists solely to allow tax processing and carries no other status.
It does not give you the right to work in America, does not affect immigration and does not make you eligible for benefits. It is a filing reference and nothing more.
The number always begins with a nine, which is how institutions recognise it. Format aside, it sits in the same box on a form as a Social Security number.
Who actually needs one?
An ITIN application suits anyone with an American filing duty who cannot get a Social Security number. That typically means a British person with American rental income, a gain on American property, or income from an American partnership.
It also reaches the non-American spouse of a citizen where the couple want to file jointly. The spouse needs a number before you can make that election.
Our guide to a nonresident alien spouse covers that election. The ITIN application is usually the first step in it.
Who does not need one?
Most British investors in American shares. Tax taken at source settles the bill, the broker needs only your British tax reference, and no return falls due. An ITIN application would achieve nothing for them.
People often apply unnecessarily because a form has a box for it. A W-8BEN asks for a foreign tax identifying number, and your National Insurance number fills that box perfectly well.
Check first whether you owe a return at all. An unnecessary application wastes months.
A worked example
The figures below are illustrative. They describe a pattern rather than a specific person.
Elena is British, lives in Cardiff and inherited a small apartment in Florida that she now rents out. The rent is about $14,000 a year.
She has an American filing obligation on that rental income and no Social Security number. With no tax number she cannot file. Without filing she cannot make the election that taxes her on net rent rather than gross.
Her ITIN application therefore goes in alongside her first American return. The two travel together, because the IRS rarely issues a number on its own.
Once issued, the number stays with her permanently provided she keeps filing. She uses it on every American return from then on.
What is Form W-7?
The ITIN application itself is a single page asking for your name, address, date of birth, country of citizenship and the reason you need a number. You pick the reason from a short list.
Picking the right one matters, because it sets what proof you must send. A category chosen carelessly is a common cause of rejection.
The form goes with your tax return rather than separately, in most cases. The return is the evidence that you genuinely need the number.
The document routes compared
The table sets out the three ways of proving identity. Only one of them involves parting with your passport.
| Route | What you send | Passport risk |
|---|---|---|
| Post originals | Your actual passport | Out of your hands for weeks |
| Certifying acceptance agent | Certified copies | None |
| Issuing agency copy | Copy certified by the passport office | None |
| IRS Taxpayer Assistance Centre | In person verification | None, but requires US travel |
| Notarised copy | Not accepted on its own | Not applicable |
| Solicitor certified copy | Not accepted on its own | Not applicable |
Do you really have to post your passport?
No, and this is the single most useful thing to know about an ITIN application. A certifying acceptance agent can verify your original documents in person and send certified copies instead.
Agents are approved firms, many of them British accountants, who hold an IRS agreement to check documents. You attend with your passport and leave with it.
The alternative is a copy certified by the issuing agency itself, which for a British passport means the passport office. That route works but is slower to arrange.
Why are notarised copies rejected?
Because an ITIN application needs certification by the issuing agency or an approved agent. A notary is neither. A solicitor or notary copy that would satisfy a British institution is simply not accepted here.
This catches people constantly, because notarisation feels like the obvious answer. The application comes back months later with the documents and no number.
Establish the route before paying anyone to certify anything.
How long does it take?
An ITIN application usually takes seven to eleven weeks once a complete package reaches the IRS, and longer during the filing season when volumes peak. Build that into any deadline you are working to.
A rejected application restarts the clock entirely. That is why getting the category and the evidence right first time matters more than speed.
Apply well before you need the number rather than against a deadline.
Can an ITIN expire?
Yes. A number you do not use on a federal return for three years in a row lapses at the end of the third year. Using it after that means a fresh ITIN application, with all the same evidence.
Renewal uses the same form and the same evidence requirements, so it is no simpler than the original application. The passport problem returns with it.
If you expect a gap in filing, that expiry is worth planning around.
Does it affect your immigration position?
Not at all, in either direction. An ITIN application gives you no right to enter, work or remain in America, and applying for one does not prejudice any future visa application.
The IRS issues it for tax administration and shares it for that purpose. It is not an immigration document and is not treated as one.
People sometimes avoid applying for fear of consequences. That fear is misplaced. Not filing is the bigger risk.
What about children and dependants?
They can hold numbers too. A child often needs one where a parent claims them on an American return. The rules on proof are tighter for a child than for an adult, so plan for extra papers.
A passport alone usually does for a child. Where it carries no entry stamp, you may need extra records. Medical or school records can fill that gap.
Our guide to the child tax credit from abroad covers when a number becomes necessary.
What if the application is rejected?
You get a notice saying why, and you can apply again once you fix it. Most failures come down to three things: the wrong category, thin evidence, or a missing return. Each one is avoidable.
The return attached to a rejected application is usually still treated as filed, which protects you on deadlines. The number waits until you fix the problem.
Read the notice carefully rather than resubmitting the same package. A second identical application fails for the same reason.
Does a British company need one?
No. A company needs an employer identification number, which is a different reference from a different process. An ITIN application will not help a corporate filing at all, and the two get mixed up often.
People mix the two up often, above all British firms selling into America. An individual number will not work for a corporate filing.
Our guide to US sales tax for UK sellers covers the business registrations that do apply.
What does it cost?
The IRS charges nothing to issue the number. Your cost sits in the certification appointment and the return that travels with it, since the two almost always go together in one package.
A certifying acceptance agent charges a fee for the verification appointment, usually a modest one against the value of keeping your passport. For a family applying together that fee multiplies.
Set it against the alternative. Being without a passport for two months during the 2025 filing season has its own cost.
Can you apply before you need to file?
Rarely. The IRS wants to see why you need the number, and a return is the proof. A few exceptions exist, mostly where a treaty claim or a bank requires one, and each needs its own supporting letter.
So in most cases the ITIN application waits until the return is ready. That feels backwards and it is simply how the process runs.
Plan the two as one job rather than two.
What if you later get a Social Security number?
You stop using the old one and tell the IRS to merge your records. The Social Security number takes over, and the earlier number is retired rather than running alongside it.
Doing this keeps your filing history in one place. Two live references on one person causes matching problems later.
Write to the IRS with both numbers once the new one arrives.
Does the whole family apply together?
They can, and it is usually simpler. One return can carry several forms, with each person supplying their own proof of identity inside the same package sent to the IRS.
The cost rises with each person, because a certifying agent charges per appointment. Four people means four sets of fees.
Book them together so nobody has to repeat the trip.
What happens to the papers you send?
Certified copies stay with the IRS and never come back. Original passports are returned eventually, though that wait is exactly what the certified route exists to avoid in the first place.
Keep your own copy of everything you submit. If the file goes missing you will need to rebuild it quickly.
Scan the whole package before posting.
Is an ITIN worth having if you may not file again?
Often yes, because a one-off American gain or inheritance rarely stays one-off. Property in particular tends to throw off income first and a sale later, and each of those needs a return.
The number lapses after three unused years, so it is not a permanent asset. It is still easier to renew than to start again from nothing.
Weigh it against the chance of a second American event.
What does the whole thing cost in practice?
The number itself is free. In 2025 a certifying agent appointment typically runs to a few hundred pounds per person, and the return that goes with it is priced on its own complexity.
Set that against posting a passport to Texas in filing season. For anyone who travels, the fee buys back two months of freedom.
For a family the sums shift, because the fee repeats per head.
How to apply
- Confirm you actually have an American filing obligation.
- Check whether a Social Security number is available to you instead.
- Identify the correct category on the application form.
- Prepare the American tax return that will accompany it.
- Book an appointment with a certifying acceptance agent.
- Attend with your original passport and leave with it.
- Submit the form, the certified copies and the return together.
- Allow seven to eleven weeks, longer in filing season.
Mistakes and penalties we see with an ITIN application
The first is sending a notarised copy of a passport. It fails every time. The papers come back months later and nothing has moved.
The second is applying without a return attached. You get the number because you must file. An ITIN application on its own usually fails.
The third is applying when you need no number at all. An investor whose only American income is withheld dividends rarely needs one.
The fourth is letting a number lapse through three years of non-filing and discovering it at the worst moment.
How US UK Tax Accountants helps
We confirm first whether an ITIN application is needed at all, because a surprising number of applications are unnecessary. Where you do need one, we handle the category, the proof and the return that goes with it.
We arrange certification so your passport never leaves Britain. Our US federal return service covers the return that travels with the application.
If an American form has asked for a tax number you do not have, get in touch. The route matters more than the form.
Last reviewed 12 October 2026. This article is general information and not personal tax advice. Every case turns on its own facts, so take advice on yours before applying.
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Official guidance from the IRS, FinCEN and GOV.UK. Thresholds and rates on those pages are updated annually — check the current tax year before relying on a figure.
