- Who CA8421 is for
- The rule behind it: one country at a time
- CA8421 compared with the other abroad forms
- What you'll need before you start
- How to apply
- The healthcare bonus
- What the certificate isn't
- Countries outside the EU arrangement
- If you're covered by the Withdrawal Agreement
- Voluntary contributions while you're abroad
- The verdict
- Frequently asked questions
CA8421 is HMRC's application for a certificate confirming you pay UK National Insurance when you work in 2 or more countries, usually the UK plus one or more EU countries, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland. The certificate shows the other country you don't need to pay its social security contributions as well.
This guide follows HMRC's CA8421 guidance and GOV.UK's National Insurance abroad guidance, as of October 2026.
Who CA8421 is for
- You live in the UK and work in 2 or more countries across the UK, the EU, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland.
- You live in an EU country, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland and work only in the UK.
- You're flight or cabin crew and your home base is in the UK.
- You need evidence that UK social security law applies to you, for example you only live or work in the UK but sell or rent out a property, or keep a professional status, in one of those countries.
That last group surprises people. A UK freelancer who lets a flat in Spain or keeps a professional registration in Ireland can use CA8421 to get written proof that they belong to the UK system.
The rule behind it: one country at a time
GOV.UK says that if you work across the UK and the EU, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland, you only pay into one country's social security scheme at a time. You usually pay where you work. You only pay UK National Insurance for that work if HMRC has issued a certificate of coverage, sometimes called a PDA1. CA8421 is the route to that certificate when the work is split between countries.
CA8421 compared with the other abroad forms
| Situation | Form |
|---|---|
| Working in 2 or more countries at the same time | CA8421 |
| Employer sending staff to work temporarily in an EU or partner country | CA3821 |
| Applying for a certificate confirming you pay UK National Insurance while working temporarily abroad | CA3822 |
If you're not sure which applies, HMRC's guidance points to its interactive tool that checks which application you need, including for countries with their own social security agreement with the UK.
What you'll need before you start
- Your country and place of birth, any previous name and every nationality you hold.
- Your employer's details if you're employed, or your business details if you're self-employed.
- Where you carry out your work activities.
- If relevant, the type of UK right to work you hold and whether you held it before 1 January 2021.
- If relevant, your partner's EU Settlement Scheme status, and any right to reside in an EU or partner country, with whether you held it before 1 January 2021.
How to apply
You apply online and you'll need to sign in, or create sign-in details. You don't have to finish in one go: you can save your answers and come back. An agent applies with their own sign-in details, and the client fills in form 64-8 to authorise them, which is sent with the CA8421 application. HMRC also has a tool that shows when you can expect a reply.
The healthcare bonus
If you live in an EU country, Iceland, Liechtenstein, Norway or Switzerland and get a certificate confirming you pay UK National Insurance while working in any of those countries, HMRC also issues an S1 healthcare entitlement certificate. That can give you health cover in your country of residence funded by the UK, which is worth knowing before you sign up for private cover.
What the certificate isn't
GOV.UK is clear that a certificate of coverage is not a work permit. UK citizens need permission to work in most of these countries, so check with that country's embassy in the UK. It also doesn't change how much you pay: your contributions still follow the normal UK National Insurance rates, and if you're self-employed the usual rules on Class 2 National Insurance apply.
Countries outside the EU arrangement
CA8421 covers the UK plus the EU, Gibraltar, Iceland, Liechtenstein, Norway and Switzerland. For other countries, GOV.UK says it depends on whether the country has a social security agreement with the UK. If it does, you'll need that agreement's own certificate of coverage to show you pay in the UK. If it doesn't, you pay UK National Insurance for the first 52 weeks of working abroad when you're working there temporarily, your employer has a place of business in the UK, you're ordinarily resident in the UK and you lived here immediately before the work started.
If you're covered by the Withdrawal Agreement
Some people keep the older rules. GOV.UK says you're covered by the social security provisions of the EU Withdrawal Agreement if, for example, you're a UK national who was resident or started working in an EU country before 1 January 2021 and have lived or worked there ever since, or an EU national who was resident or working in the UK before that date, including with EU Settlement Scheme status. That's why the application asks whether your right to work or reside started before 1 January 2021.
Voluntary contributions while you're abroad
If you don't have to pay UK Class 1 contributions and aren't treated as having paid Class 2, GOV.UK suggests thinking about voluntary National Insurance to protect your State Pension. You can only contribute voluntarily to one social security system at a time.
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The verdict
If your working week crosses a border between the UK and an EU or partner country, CA8421 is the form that stops two countries asking for social security on the same earnings. Apply before the work starts if you can, gather your nationality and right-to-work details first, and keep the certificate where you can show it to a foreign authority on request.
Employers in that position should also read our guide to telling HMRC about staff abroad.
Frequently asked questions
What is CA8421?
It's HMRC's application for a certificate confirming you pay UK National Insurance when working in 2 or more countries, such as the UK and an EU country.
Who should use CA8421?
People living in the UK and working in 2 or more of the UK, EU, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland, people living in those countries who only work in the UK, and UK-based flight or cabin crew.
Is CA8421 the same as an A1 certificate?
It's the application for a certificate of coverage, which GOV.UK also refers to as a PDA1, for people working in more than one country.
Can I apply for CA8421 online?
Yes. You apply online, sign in, and can save your answers and return later.
Do I get healthcare cover with a CA8421 certificate?
If you live in an EU country, Iceland, Liechtenstein, Norway or Switzerland and get the certificate, HMRC also issues an S1 healthcare entitlement certificate.
Is a certificate of coverage a work permit?
No. You may still need a work permit to work in the other country.
