CA3821: Telling HMRC You're Sending Employees to Work Abroad

This guide follows HMRC's CA3821 page and GOV.UK's guidance on National Insurance for work in the EU and partner countries, as of October 2026.

Why employers file it

Under the UK's social security agreements with the EU, Gibraltar, Iceland, Liechtenstein, Norway and Switzerland, a worker only pays into one country's scheme at a time, and usually that's the country where they're working. GOV.UK adds that an employer's liability follows the employee's. So unless HMRC issues a certificate of coverage, a UK employee posted to France or Germany would normally fall into that country's system, and so would their employer's contributions. CA3821 is the employer's route to keeping them in the UK system.

Who qualifies for a certificate

GOV.UK says a certificate should be applied for when an employee is employed in the UK by an employer who normally carries out its activities in the UK, and is going to work temporarily in an EU country for up to 2 years. The employer must have sent them, or agreed to them working there temporarily. The same up-to-2-years rule applies to Gibraltar, Iceland, Liechtenstein, Norway and Switzerland.

The new-business rule

Here's the detail most guides miss. If your business has been trading in the UK for less than 18 months, HMRC wants extra information with the application, for example a sample of invoices or contracts from the last 2 months. That's how HMRC checks you're an employer that normally operates in the UK and not a shell set up to post staff abroad. Have those documents ready to upload before you start, or the application will stall.

How to apply

Route	Who uses it	Notes
Online form	Employers	Sign in with a Government Gateway user ID, or get a confirmation code by email
Agents online form	Agents acting for an employer	Same sign-in options
Print and post form	Anyone who prefers paper	Filled in on screen, can't be saved part way, then printed and posted

Gather everything first if you use the print and post version, because you can't save your progress. HMRC has a tool showing when you can expect a reply.

CA3821, CA3822 or CA8421?

Form	Use it when
CA3821	An employer is sending staff to work temporarily in the EU, Norway, Iceland, Switzerland or Liechtenstein
CA3822	Someone needs a certificate confirming they pay UK National Insurance while working temporarily abroad
CA8421	Someone works in 2 or more countries at the same time

If an employee splits their time between several countries in the same period rather than taking one temporary posting, the multi-state form CA8421 is usually the better fit. HMRC's interactive guidance tool will tell you which one to use.

What happens to payroll

Once a certificate is in place, you keep running the employee through UK payroll and deducting National Insurance as normal, at the usual National Insurance rates, with employer's National Insurance on top. The certificate is the evidence you show the other country's authority that no contributions are due there.

Postings outside these countries

For a country with no social security agreement with the UK, GOV.UK says an employee pays UK National Insurance for the first 52 weeks of working abroad if all of these apply: the work is temporary, the employer has a place of business in the UK, the employee is ordinarily resident in the UK, and they lived in the UK immediately before starting work abroad. Countries with their own agreement with the UK have their own certificate process.

Things the certificate doesn't do

• It isn't a work permit. GOV.UK says UK citizens need permission to work in most of these countries, so check with the country's embassy.
• It doesn't cover postings longer than 2 years under the standard rule. Longer arrangements are only agreed between HMRC and the other country in exceptional circumstances.
• It doesn't replace the employee's own tax position in the other country, which is a separate question.

Other workers the rules cover

The same certificate rules on GOV.UK also cover a civil servant working for the UK government in an EU country, people working on board a UK-flagged vessel in certain circumstances, and flight or cabin crew whose home base is in the UK. If your posted staff fall into one of these groups, check the guidance tool before you choose a form.

Voluntary contributions for long postings

If an employee won't be paying UK Class 1 contributions while abroad, GOV.UK suggests they think about paying voluntary National Insurance contributions to protect their benefit entitlement and State Pension. They can only contribute voluntarily to one social security system at a time, and voluntary contributions don't cover health insurance in the country where they live.

The verdict

CA3821 is a small admin step that protects both the employee's UK contribution record and the employer from a second social security bill. Apply before the posting starts, keep invoices and contracts ready if the business is under 18 months old, and use CA8421 instead for staff who work across several countries at once.

Frequently asked questions

What is CA3821?

It's the HMRC form employers or agents use to tell HMRC they're sending employees to work temporarily in an EU country, Norway, Iceland, Switzerland or Liechtenstein.

How long can an employee be posted under CA3821?

GOV.UK describes temporary work for up to 2 years for an employee of an employer who normally carries out its activities in the UK.

What extra evidence do new businesses need for CA3821?

If the business has traded in the UK for less than 18 months, include extra information such as a sample of invoices or contracts from the last 2 months.

Can an agent apply for CA3821?

Yes. Agents have their own online form, and there's also a print and post version.

Is CA3821 the same as CA8421?

No. CA3821 is for employers posting staff temporarily abroad, while CA8421 is for people working in 2 or more countries at the same time.

Does the employee still pay UK National Insurance?

Yes. With a certificate of coverage, the employee stays in UK National Insurance and doesn't pay social security in the other country.