Form 6166 is a letter from the US Treasury certifying that you are a US resident for tax treaty purposes. A US resident with UK income, such as a UK pension, uses it to claim relief from UK tax under the UK-US Income Tax Treaty. You request it on Form 8802. The user fee is $85 for an individual, and the IRS recommends applying at least 45 days before you need the certificate.
Treaty relief is not automatic. A UK pension provider or HMRC will keep deducting UK tax until someone proves that the recipient is resident in the other country. For people living in the US, that proof is Form 6166. This guide explains who can get one, how the application works alongside HMRC's own claim form, and why a US citizen living in Britain usually cannot use it. It covers individuals; companies follow a similar but separate process.
What Form 6166 is and who needs it
Form 6166, Certification of U.S. Tax Residency, is printed on US Department of the Treasury letterhead. It states that the person named is a resident of the United States for purposes of US taxation for a given year. The IRS describes it on its Form 6166 page. Foreign tax authorities and payers rely on it to grant treaty benefits.
Typical UK situations
The most common user is someone who worked in the UK, moved to the US and now draws a UK pension. Under Article 17 of the treaty, a pension paid to a US resident is generally taxable only in the US. Other users include US residents receiving UK interest or royalties, and US companies receiving UK-source payments. In each case, UK tax is reduced or removed only once residence is certified.
| Person | Certificate needed | Issued by | Purpose |
|---|---|---|---|
| US resident with a UK pension | Form 6166 | IRS | Stop UK tax under Article 17 |
| US resident with UK interest or royalties | Form 6166 | IRS | Claim 0% UK tax under Articles 11 and 12 |
| UK resident with US dividends | Form W-8BEN to the payer | Self-certified | Reduce US withholding to 15% |
| UK resident needing proof for a US or third-country claim | Certificate of residence | HMRC | Prove UK treaty residence |
| UAE resident | Tax Residency Certificate | UAE Federal Tax Authority | Claim relief under the UAE's treaties |
How to apply: Form 8802
You apply on Form 8802, Application for United States Residency Certification. The Instructions for Form 8802 set out the requirements.
The fee and timing
The user fee is $85 per Form 8802 for an individual, regardless of how many countries or years are requested on that form (IRS, Instructions for Form 8802). It is non-refundable, and the IRS will not process the application until it is paid. The IRS asks you to apply at least 45 days before you need the certificate. In practice, allow longer in the early months of the year.
The return requirement
The IRS certifies residency by checking that you filed the appropriate return, usually Form 1040, for the year concerned. If you request certification for the current year before a return is due, you must normally include a signed statement, under penalties of perjury, that you are a US resident and will remain one throughout the year. If the return is missing, the IRS can refuse the application.
Authorising someone to apply for you
A tax adviser can submit Form 8802 for you if they hold a valid power of attorney on Form 2848 or an authorisation on Form 8821 covering the year. The form has a section for third-party appointees.
Using Form 6166 with HMRC
For UK relief, the certificate works together with an HMRC claim form. A US-resident individual uses HMRC's form US-Individual 2002, which covers UK pensions, purchased annuities, interest and royalties. HMRC publishes it on its Form US-Individual 2002 page.
The sequence
First, you complete form US-Individual 2002. Next, you send it to the IRS with Form 8802 and the fee. The IRS then certifies your US residence and forwards the claim to HMRC. Finally, HMRC issues an "NT" (no tax) code to your pension provider and repays any UK tax over-deducted for earlier years within the time limit. Our guide to UK pension drawdown and US tax explains what happens once the NT code is in place.
How long relief lasts
An NT code normally continues until your circumstances change. However, HMRC can ask for fresh evidence, and a new provider may need a new claim. Therefore, keep a copy of the certificate and note the year it covers.
Why US citizens living in the UK usually cannot use it
Form 6166 certifies treaty residence, not citizenship. A US citizen who is resident in the UK under the treaty's tie-breaker rules is not a US resident for treaty purposes, so the IRS will not generally certify them for a claim against UK tax. In any case, the UK taxes them as a resident. Their protection comes from foreign tax credits and the treaty's saving clause exceptions, as our guide to the saving clause exceptions explains.
The UAE
The US has no income tax treaty with the UAE, so Form 6166 does not reduce any income tax there. A UAE resident who needs to prove residence for the UAE's own treaties, including the UK-UAE agreement, applies to the Federal Tax Authority instead. Our guide to the UAE Tax Residency Certificate covers that process, and our cross-border taxation page explains how residence is decided in each country.
An illustrative case
Consider an illustrative British engineer who retired to Arizona in 2025 and draws £24,000 a year from a UK workplace pension. The figures are illustrative. His provider deducts UK tax under PAYE. In early 2026, he completes form US-Individual 2002 and sends it to the IRS with Form 8802 and the $85 fee. The IRS certifies his residence and passes the claim to HMRC, which issues an NT code and refunds the UK tax deducted since he became US resident. From then on, he reports the pension only on his US return. Our US tax on UK pensions page covers that reporting.
If UK tax is being deducted from income that the treaty says should be taxed only in the US, book a consultation with our US-UK treaty team. We prepare Form 8802 and the HMRC claim together.
Frequently Asked Questions
What is Form 6166?
Form 6166 is a certification of US tax residency issued by the IRS on US Treasury letterhead. It confirms that a person is a US resident for tax purposes for a stated year, so that a foreign tax authority or payer will grant benefits under a tax treaty.
How do I get Form 6166?
Apply on IRS Form 8802, Application for United States Residency Certification, and pay the user fee. The IRS checks that you have filed the appropriate US tax return for the year and then issues Form 6166.
How much does Form 6166 cost?
The user fee is $85 per Form 8802 for an individual applicant, regardless of the number of countries or years requested on that form (IRS, Instructions for Form 8802). The fee is non-refundable.
How long does Form 6166 take?
The IRS recommends submitting Form 8802 at least 45 days before the certificate is needed. Processing can take longer at busy times of the year, so apply early.
Which HMRC form do US residents use to stop UK tax on a pension?
A US-resident individual uses HMRC form US-Individual 2002. It is sent to the IRS with Form 8802. The IRS certifies US residence and forwards the claim to HMRC, which then issues a no-tax code to the pension provider.
Can a US citizen living in the UK get Form 6166?
Generally not for a claim against UK tax. Form 6166 certifies residence for treaty purposes, and a US citizen who is treaty-resident in the UK is not a US resident under the treaty. Their relief comes from foreign tax credits instead.
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