National Insurance When Working in Multiple Countries

Introduction

If you work in the UK and one or more other countries at the same time, you need to establish which country's social security system you should pay into. You can apply for a certificate (form CA8421) to confirm your position and avoid paying National Insurance contributions in multiple countries unnecessarily.

Who needs to apply for a CA8421 certificate

You should complete a CA8421 form if you fall into one of these situations:

• You live in the UK and work in two or more countries across the UK, EU, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland
• You live in an EU country, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland, but only work in the UK
• You work as flight or cabin crew and your home base is in the UK
• You need proof that you're subject to UK social security rules — for example, you only live or work in the UK but rent out property or maintain a professional status in the EU, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland

If you're unsure whether you need to apply for this particular certificate, you can use HMRC's online tool to check how to apply for a National Insurance certificate when working abroad, particularly if the countries involved have specific social security agreements with the UK.

Information you'll need to provide

When completing the CA8421 form, you must provide:

• Your country and place of birth
• Your previous name if you've changed it
• Which nationalities you hold
• Your employer's details if you're employed
• Your business details if you're self-employed

Depending on your circumstances, you may also need to include:

• Whether you hold a right to work in the UK — if so, you'll need to specify the type of right to work and whether you held this right before 1 January 2021
• If you have a husband, wife or partner with an EU Settlement Scheme status — if so, you'll need to provide their details
• Whether you have a current right to reside in an EU country, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland — including whether you held this right before 1 January 2021
• Where you carry out your work activities

Healthcare entitlement

If you're resident in an EU country, Iceland, Liechtenstein, Norway or Switzerland and your certificate of coverage confirms that you pay UK National Insurance while working in any of those countries, you may be entitled to healthcare funded by the UK in your country of residence.

When HMRC issues your certificate confirming UK National Insurance coverage, they will also issue you with a healthcare entitlement certificate (known as an S1 form).

How to apply

You can apply online through HMRC's digital service. You'll need to sign in to use this service, and if you don't already have sign-in details, you can create them when you start your application.

You don't have to complete the form in one sitting — you can save your answers and return to finish it later.

If you're using an accountant or agent

If your accountant or agent is applying on your behalf, you need to complete an authorising your agent form (form 64-8) first. Your agent should submit the completed 64-8 form alongside your CA8421 application.

When your agent applies, they should use their own sign-in details rather than yours.

After you apply

Once you've submitted your application, you can check HMRC's guidance to find out when you can expect a reply about your application. Processing times can vary depending on the complexity of your circumstances and the countries involved.

Why this matters

Having the correct certificate is important for several reasons:

• It prevents you from paying social security contributions in multiple countries when you only need to pay in one
• It provides official documentation that you can show to foreign tax authorities or employers
• It ensures you're building up the correct social security entitlements in the right country
• It may unlock healthcare benefits in your country of residence

Working across borders creates complex social security obligations. The rules exist to ensure you're protected in one country's system rather than falling between multiple systems or paying twice for the same protection.

Sources

• Apply for a certificate to confirm you pay UK National Insurance when working in 2 or more countries (CA8421)

This article provides general guidance based on current HMRC rules. For advice specific to your situation, speak to your accountant.