UTR Number for Americans in the UK: How to Get One and How Long It Takes

A UTR number is HMRC's 10-digit Unique Taxpayer Reference, and Americans in the UK only get one by registering for Self Assessment. It does not come with a National Insurance number or a UK job. HMRC says it usually arrives by post around 15 days after registering, and longer if you live overseas.

Americans arriving in the UK are used to one number doing everything. In the US, the Social Security number is the key to the payroll, the tax return and the bank account. The UK splits those jobs between two numbers, and the one that files a tax return is the one most new arrivals do not have. This guide explains what the UTR is, how to get it, how long it takes and what to do with it once it arrives. If you are still working out whether you need a return at all, start with our guide to whether you need to file Self Assessment in the UK.

What is a UTR number?

A UTR number is the reference HMRC uses for your Self Assessment account. GOV.UK describes it on its find your UTR number page as a 10-digit number you get when you register for Self Assessment or set up a limited company. Individuals and companies have separate UTRs: a company's Corporation Tax UTR is not the director's personal UTR, and the two are never interchangeable.

The UTR stays with you. Once HMRC has issued it, the same number is used every year you file, and it is reused if a dormant Self Assessment record is later reactivated. An adviser dealing with HMRC on your Self Assessment will ask for it too.

UTR, National Insurance number and Social Security number compared

Much of the confusion comes from expecting a UK equivalent of the Social Security number. There is not one. The table sets out which number does which job.

Number	Issued by	What it is for	How you get it
UTR (Unique Taxpayer Reference)	HMRC	Self Assessment: filing a UK return, paying the tax, authorising an adviser	Register for Self Assessment
National Insurance number	UK government (apply on GOV.UK)	National Insurance contributions, PAYE and employment records	Apply once you live and have the right to work in the UK; may already appear on a BRP or eVisa
Social Security number	US Social Security Administration	US taxpayer identification on IRS returns	Already held by US citizens
Company UTR	HMRC	Corporation Tax for a limited company	Issued when the company is set up

GOV.UK says you can apply for a National Insurance number if you live in the UK, have the right to work here, and are working, looking for work or have an offer of work. It can take up to four weeks, and anyone with a biometric residence permit or an eVisa may already have one shown on it. On the US side, the IRS explains on its taxpayer identification numbers page that the Social Security number is issued by the Social Security Administration and that a TIN must be furnished on US returns. The UTR does not replace it, and the Social Security number means nothing to HMRC.

How do Americans in the UK get a UTR number?

Americans in the UK get a UTR number by registering for Self Assessment with HMRC. There is no separate application for the number itself. The registration tells HMRC why you need to file and from when, and the UTR is issued as a result.

1. Confirm you need to file. The usual triggers for Americans are income PAYE does not tax: US dividends and interest, rent on a US property, self-employment income, or a capital gain.
2. Sort out your National Insurance number early. If you work in the UK you will usually need one anyway, and GOV.UK says it can take up to four weeks to arrive.
3. Register through the right route. Individuals with a Personal Tax Account can use HMRC's online service. People who are not self-employed can also use form SA1, and self-employed people register as sole traders. Our guide to registering for Self Assessment by 5 October covers the routes and the deadline in detail.
4. Wait for the UTR. Keep a record of the date you registered. If the expected time passes, check HMRC's reply times rather than registering again.
5. Set up online filing. The UTR identifies the account, and you still need online access to file the return itself.

Illustrative example: an American engineer who moved to Bristol in September 2025 already had a National Insurance number shown on her eVisa and was paid through PAYE. Her US brokerage account paid dividends through the year, so she needed a UK return for 2025/26. She registered online through her Personal Tax Account in early September 2026, her UTR appeared in the account, and she could then file online before 31 January 2027 and pay using her UTR with the letter K as the reference.

How long does it take to get a UTR?

A UTR usually takes around 15 days to arrive by post after you register, and HMRC says it takes longer if you live overseas. That timing appears on GOV.UK's find your UTR number page, and it is the realistic timetable for anyone registering on paper or through an adviser.

The faster route is recent. On 9 September 2026 HMRC announced an improved Self Assessment registration service for individuals with a Personal Tax Account, which puts the UTR in the online account within 72 hours instead of up to 15 days by post. The announcement makes clear that agents cannot use the new service and continue to register clients on forms SA1 or CWF1.

The timing matters because of the calendar. For the tax year that ended on 5 April 2026, anyone filing for the first time must tell HMRC by 5 October 2026, and the online return is due by 31 January 2027, according to HMRC's Self Assessment deadlines. The UTR is the first link in that chain, and posted codes for online access can add more time after it.

Where to find your UTR if you have lost it

HMRC lists three places an individual's UTR appears:

• your Personal Tax Account on GOV.UK;
• the HMRC app;
• previous tax returns and other HMRC documents, such as payment reminders.

If none of those works, HMRC's instruction is to contact it. The one thing not to do is register again as a way of getting a new number. GOV.UK's registration page separately warns that anyone registered in an earlier year who did not file last year may need to reactivate their existing account rather than start a new one.

What you use the UTR for

Filing the return

The UTR identifies the Self Assessment record the return is filed against. Without it you cannot file the return against your account.

Paying HMRC

Self Assessment payments carry an 11-character payment reference, which HMRC's bank details page describes as the 10-digit UTR followed by the letter K. HMRC publishes separate account details for payments from UK and overseas bank accounts. Americans paying from a US account should take the details from that page on the day they pay, rather than from an old letter or a third-party website, and allow for the time an international transfer takes. HMRC says Faster Payments usually arrive the same or next day, CHAPS the same working day and Bacs in three working days.

Authorising an adviser

An adviser acting on your UK taxes will ask for your UTR in order to deal with HMRC about your Self Assessment account. Keep it with the rest of your cross-border paperwork, next to your Social Security number and US return copies.

What happens to your UTR when your circumstances change?

A UTR belongs to one person and follows that person through changes in their circumstances. Three changes come up most often for Americans in the UK.

Marriage or a spouse who also needs a return

The UK taxes spouses and civil partners as individuals, and there is no UK equivalent of the US joint return. If both of you need to file, each of you registers for Self Assessment, each gets a separate UTR and each files a separate return. That is often the opposite of what an American couple expects, especially when they file jointly with the IRS. Joint accounts and jointly owned property are split between the two UK returns according to each person's share, while the US return may still combine them. Our guide to tax planning for US/UK couples covers how those two treatments interact.

Leaving the UK

Moving back to the US does not cancel your UTR. The departure year usually needs a UK return to record the date you left and any split-year claim. GOV.UK also confirms that people who are not UK resident usually still pay UK tax on UK income such as rent and some savings interest. An American who keeps a London flat after moving home may therefore go on filing under the same UTR for years, and should keep it with their US tax records rather than assuming the UK side has ended.

Setting up a UK company

A founder who incorporates a UK limited company gets a separate company UTR for Corporation Tax, and HMRC sends it to the registered office address. The founder's personal UTR is unchanged and is still used for their own return, which will now include salary or dividends from the company. Keeping the two numbers apart on every payment and letter avoids money landing in the wrong account. Our guide to UK Self Assessment for Americans covers how the UK return itself fits with your US one.

Common UTR mistakes Americans make

• Assuming the National Insurance number is enough. It runs your payroll record but does not file a return.
• Waiting until January to register. The 5 October deadline comes first, and the post takes about 15 days, longer to an overseas address.
• Registering twice. A lost or late UTR is a reason to check with HMRC, not to start a new registration.
• Mixing up company and personal UTRs. Founders with a UK limited company have two, and payments made against the wrong one land in the wrong account.
• Dropping the K. HMRC asks for the 11-character reference, so use it every time.

Our tax obligations checklist for Americans living in the UK shows where the UTR sits alongside the US return, FBAR and other filings.

Getting your UTR and first return in place

US/UK Cross Border Tax is US CPAs and UK tax advisers working as one team, with offices in London, Manchester, New York and San Francisco. For Americans in the UK we register clients for Self Assessment on the right basis, obtain the UTR, and prepare the first UK return with the US return in view so that residence dates and foreign tax credits agree.

If you need a UTR number as an American in the UK and a first return filed on time, see our UK Self Assessment service, read how we work with Americans living in the UK, or contact us with your arrival date and income sources.