US-UK Social Security Totalization Agreement: What US Expats Need to Know

The US-UK Social Security Totalization Agreement is a bilateral treaty that coordinates the social security systems of the United States and the United Kingdom. For US citizens and green card holders working in the UK — whether employed, self-employed, or sent on assignment — this agreement determines which country’s social security contributions apply, prevents dual contributions on the same income, and protects benefit entitlements built up in both countries.

Understanding the Totalization Agreement is essential for US expats working in the UK, UK employers of US workers, and Americans approaching retirement who have worked in both countries.

What Is the Totalization Agreement?

The US-UK Totalization Agreement, which has been in force since 1985, addresses two primary problems that arise when workers move between countries:

• Dual coverage: Without an agreement, a worker could be required to pay social security taxes to both countries on the same income — a significant financial burden for mobile workers.
• Gap in coverage: Workers who divide their careers between countries may not work long enough in either to qualify for retirement, dISAbility, or survivor benefits. The Totalization Agreement allows work credits from both countries to be combined (“totalized”) for benefit eligibility purposes.

Which Social Security Systems Does It Cover?

The agreement covers the following systems:

• US side: Social Security (OASDI — Old-Age, Survivors, and Disability Insurance) and Medicare Hospital Insurance (HI)
• UK side: National Insurance contributions (NICs) which fund the UK State Pension, Statutory Sick Pay, Statutory Maternity/Paternity/Adoption Pay, and other state benefits

The UK system is divided into contribution classes. Class 1 NICs are paid by employees and employers on employment income. Class 2 and Class 4 NICs apply to self-employed individuals. The agreement covers all of these.

Which Country’s System Applies to You?

The primary rule is the territoriality principle: you pay into the social security system of the country where you perform your work, regardless of where you or your employer are based. If you work in the UK, you pay UK NICs (and your employer pays employer NICs). You do not pay US Social Security taxes on the same employment income.

However, there are several important exceptions:

• Temporary assignments: If a US employer sends a worker to the UK for a temporary assignment expected to last five years or less, the worker may remain covered under the US Social Security system and be exempt from UK NICs. A Certificate of Coverage (Form SSA-2497) must be obtained from the US Social Security Administration to certify this.
• Self-employed workers: Self-employed individuals are generally covered by the system of the country in which they are resident. A US citizen self-employed in the UK is generally subject to UK Class 2/Class 4 NICs, not US Self-Employment Tax — though this must be documented correctly.
• Government employees: US government employees working in the UK remain covered by the US Social Security system, regardless of how long the posting lasts.

Certificate of Coverage: How to Claim the US Exemption

If you are a US employee sent to work in the UK and your employer wants you to remain in the US Social Security system (rather than switching to UK NICs), your employer must obtain a Certificate of Coverage from the US Social Security Administration.

The employer completes Form SSA-2497 and submits it to the Social Security Administration’s Office of International Programs. The SSA then issues a certificate confirming US Social Security coverage for the assignment period. A copy of this certificate must be available to present to HMRC if requested — it certifies the worker’s exemption from UK NICs during the covered period.

Without the certificate, both the worker and employer may be liable for UK NICs even if they believe the Totalization Agreement exemption applies. Retroactive certificates can sometimes be obtained, but it is far better to apply before or at the start of the assignment.

Combining Credits for Benefit Eligibility

If a US citizen has not worked long enough in either the US or the UK to qualify for benefits based solely on their contributions to that country’s system, the Totalization Agreement allows credits from both countries to be combined:

• US Social Security: Requires 40 Social Security credits (approximately 10 years of work) to qualify for retirement benefits. A US citizen who worked 7 years in the US and 15 years in the UK can use both periods to meet the 40-credit threshold — and then receives a US benefit proportional to their US-only earnings record.
• UK State Pension: Requires 10 qualifying years of NICs to receive any State Pension, and 35 qualifying years for the full New State Pension (currently £221.20 per week for 2024/25). US work periods can be counted to meet the 10-year minimum threshold.

Importantly, combining credits does not increase the amount of benefit — it only helps meet the minimum qualifying period. Each country pays a benefit proportional to its own contributions record. You receive a US Social Security benefit based on your US earnings and a UK State Pension based on your UK NICs record, separately.

US Social Security Benefits Received in the UK: US Tax Treatment

US Social Security benefits received by US citizens living in the UK are subject to US income tax under the same rules that apply to US residents. Up to 85% of US Social Security benefits may be included in US taxable income depending on your combined income (adjusted gross income plus tax-exempt interest plus half of Social Security benefits).

Under the US-UK Tax Treaty, US Social Security benefits paid to UK residents who are not US citizens are taxable only in the UK. For US citizens living in the UK, the US retains the right to tax Social Security benefits under the “saving clause” — meaning US citizens cannot use the treaty to exempt their Social Security from US tax.

UK State Pension Received by US Expats: US Tax Treatment

UK State Pension income received by US citizens (whether living in the UK or elsewhere) is generally taxable for US purposes. It is reported as foreign pension income on Form 1040. The Foreign Tax Credit may offset UK income tax paid on the State Pension against US tax, preventing double taxation. The US-UK treaty (Article 17) generally allocates UK pension income to the country of residence — for US citizens living in the UK, this means UK tax applies, and the Foreign Tax Credit handles the coordination.

Frequently Asked Questions

Do I pay both US Social Security tax and UK NICs if I work in the UK?

Generally no — the Totalization Agreement’s territoriality rule means you should only pay into one system. If you work in the UK, you pay UK NICs and are exempt from US Social Security tax on the same income (assuming no Certificate of Coverage for a temporary assignment is in place). If you have a Certificate of Coverage for a US assignment to the UK, you pay US Social Security and are exempt from UK NICs.

I worked in both countries at different times. Can I combine my work history for State Pension or Social Security?

Yes. The Totalization Agreement allows both countries to count work periods from both systems to meet the minimum qualifying period for benefits. You must apply to each country’s benefits authority separately — Social Security for US benefits and the UK Pension Service for State Pension. Each country pays based on its own contribution record, with the combined records used only to establish eligibility.

I am self-employed in the UK as a US citizen. Do I pay US Self-Employment Tax?

Under the Totalization Agreement, a self-employed US citizen who is resident and self-employed in the UK is generally covered under the UK system and pays UK Class 2/Class 4 NICs. In this case, they should not also pay US Self-Employment Tax on the same income. However, properly documenting this position — including potentially obtaining a Certificate of Coverage — is important to avoid disputes with the IRS.

Does the Totalization Agreement cover UK private pensions or occupational pensions?

No. The Totalization Agreement covers only the UK National Insurance system and US Social Security. UK private pensions (including SIPPs and occupational pension schemes) are governed by the US-UK income tax treaty, not the Totalization Agreement. See our SIPP and US Tax guide for information on how UK private pensions are treated for US tax purposes.

Get Cross-Border Social Security Advice

The US-UK Totalization Agreement reduces dual-contribution burden, but maximising the benefit for your specific situation — whether you are mid-career, approaching retirement, self-employed, or working on assignment — requires understanding the interaction with your full US and UK tax position. Our advisors can review your NICs and Social Security record, advise on Certificate of Coverage applications, and model your combined retirement benefits from both countries.

Contact us today to discuss your US-UK social security and retirement planning.