Glossary
Certificate of coverage
Official document issued by an employee's home-country social-security authority that proves they remain covered there during a foreign assignment, exempting the employer and employee from paying social-security contributions in the host country under a totalisation agreement or EU coordination regulation.
A certificate of coverage is the document that proves an employee stays in home-country social security during a foreign assignment, blocking host-country contributions.
For global payroll and mobility teams, the real question isn't whether a certificate exists. It's whether the application lands with the home-country authority before host payroll opens, and whether the host EOR or local payroll provider will accept it without re-collecting contributions on day one.
The mechanic runs through bilateral totalisation agreements (the US has 30 in force) or the EU coordination regulation 883/2004. Inside the EU and EEA, the document is the A1. The UK now issues its own Portable Document A1 for postings into EU and EFTA states under the Trade and Cooperation Agreement.
Without a valid certificate, the employer pays social security in both countries. On a UK-outbound posting to France or Germany, that double-charge can add 20 to 25 per cent of gross to the assignment cost over the posting window. Global mobility programmes that treat certificate handling as a formality usually find out about the gap on the first quarterly close.
Why a certificate of coverage matters for the employer's payroll bill
The certificate isn't a tax-planning instrument. It's a contribution-routing document that tells the host country's payroll system to stop collecting social security on the assignee.
What it actually exempts
The certificate covers employer and employee social-security contributions: pension, unemployment, sickness, family, and work-injury, depending on the country pair. Income tax is unaffected and runs under the host country's residence rules and any applicable double-tax treaty.
On the home side, contributions continue at home rates. The assignee keeps building entitlement in the home social-security system without interruption, which protects their pension record and any contribution-based benefits.
What it does not cover
The certificate doesn't waive host-country income tax, payroll tax, or labour-law obligations. It doesn't avoid permanent establishment risk either; that test runs against the activity, not the social-security routing.
It also doesn't cover periods before issuance. If host payroll has already collected contributions for a quarter, the certificate fixes future cycles but the back-recovery sits with the home-country authority on a country-specific timeline.
When do you actually need to apply for one?
The trigger is any cross-border work that crosses the host country's contribution threshold. Most regimes set this at zero: a single day of paid work in-country can in principle create an obligation.
Posted-worker assignments inside the EU
EU Regulation 883/2004 Article 12 covers the standard posted-worker case: a home-country employee sent to another Member State for up to 24 months on continuous employer payroll. The A1 is issued by the home-country social-security authority and presented to the host on request.
Article 13 covers multi-state workers: someone routinely working in two or more EU countries for the same employer. The A1 issued under Article 13 names which country's social security applies, usually the country of residence if substantial activity (25 per cent or more) happens there.
Postings under bilateral totalisation agreements
Outside the EU, the certificate runs under a bilateral totalisation agreement between the home and host countries. The US-UK agreement (in force since 1 January 1985) is the standard example: typical validity is 5 years, extensible to 8 by mutual consent.
The US Social Security Administration lists 30 totalisation agreements in force, including with Germany, France, Italy, Japan, Spain, Canada, and Australia. If no agreement exists between the country pair (US-China, US-India, UK-Brazil), the certificate route doesn't apply and the employer pays in both countries.
Business-travel and short trips
Short trips below 30 days often fall under host-country administrative tolerance, but the safe default is to apply. URSSAF in France, for example, has tightened enforcement and now expects an A1 from any worker performing paid services on French soil regardless of duration.
What is the form called in each country?
The certificate has a different name and a different issuing authority in each home country. The mechanic is the same; the paperwork is not.
| Home country | Document name | Issuing authority | Typical validity | Lead time |
|---|---|---|---|---|
| United States | Certificate of Coverage | SSA Office of International Programs | 5 years; extensible to 8 | 2 to 6 weeks |
| United Kingdom (to EU/EFTA) | Portable Document A1 | HMRC NIC&EO (form CA3837) | Up to 24 months | 4 to 8 weeks |
| United Kingdom (rest of world) | Certificate of Continuing Liability | HMRC NIC&EO (form CA3822) | Treaty-dependent | 4 to 8 weeks |
| EU Member State | A1 certificate | National social-security body | Up to 24 months | 2 to 8 weeks |
| France | A1 (Article 12) via DSN | URSSAF / CLEISS | Up to 24 months | 2 to 4 weeks |
| Switzerland | A1 certificate | Compenswiss / cantonal AHV | Up to 24 months | 3 to 6 weeks |
Lead times are critical. A certificate that lands two weeks after host payroll opens still creates a recovery problem: the host system has already collected contributions that must now be reclaimed.
For the form-by-form breakdown, see the A1 form entry and the totalisation agreement entry.
What does double social security cost when you skip the application?
The exposure is the host-country employer contribution rate applied to the assignee's full host-country gross, on top of the home-country contributions still running.
| Line | Amount (GBP) | Notes |
|---|---|---|
| Base salary | £100,000 | UK assignee posted to France, 18 months |
| UK employer NI (home, A1 in place) | £12,000 | 13.8% above threshold, annual |
| French employer social charges (no A1) | £25,000 | Approx 25% URSSAF, annual |
| Avoidable double cost over 18 months | £37,500 | French charges that the A1 would block |
| Reclaim time if collected in error | 12 to 18 months | Sits in URSSAF dispute queue |
Figures are indicative. The £37,500 line is the avoidable cost on a single mid-band assignment. Across a programme of 10 or 20 outbound assignees a year, missed certificates routinely turn into six-figure recovery exposure.
For accurate scenario modelling, the employer cost burden calculator covers the per-country employer-side loading that a certificate is meant to suppress, and the employer contributions entry sets out the underlying contribution stacks by country.
How do payroll teams and EORs handle CoC requests?
Responsibility usually splits across three parties: the home-country payroll or NIC team, the EOR or host-country payroll, and the assignee. Each side needs to know which form, which authority, and which deadline applies.
| Task | Home payroll / NIC | EOR or host payroll | Employer / mobility |
|---|---|---|---|
| Decide if A1 / CoC applies | Advisory | Advisory | Decision |
| File the application | Owner | Not in scope | Supply data |
| Hold the certificate on file | Owner | Copy required | Copy required |
| Suppress host social-security collection | N/A | Owner | Approve |
| Renew or extend the certificate | Owner | Flag deadline | Decide on extension |
| Respond to host-country audit | Supply original | Owner | Brief legal |
The recurring gap is the EOR scope assumption. Most EOR contracts cover host-country payroll, not home-country certificate filing. If the assignee comes in via an EOR rather than a direct home-country payroll, the certificate often needs a separate mobility-tax provider or the home employer's in-house NIC team.
Whichapp view
Most EOR providers will accept an A1 or certificate of coverage when handed one, but few will originate the application. Treat the certificate as a home-side responsibility, not part of the host onboarding pack. Build the four-to-eight-week lead time into the assignment timeline before the offer letter goes out.
For mobility programmes, see our Deel review for how the assignment workflow handles certificate verification at host-payroll opening, and the best global payroll providers shortlist for providers that integrate home-country A1 filing into the assignment service rather than referring it out.
See our ranked shortlist of providers, scored for European compliance, pricing transparency, and onboarding speed. Updated for 2026.
View the shortlist →Certificate of coverage FAQs
Is a certificate of coverage the same as an A1 form?
Effectively yes, but the labels differ by region. Inside the EU and EEA, the document is the A1 issued under Regulation 883/2004, while the US calls its equivalent a Certificate of Coverage issued under bilateral totalisation agreements. The UK now issues a Portable Document A1 for postings into EU and EFTA states and a Certificate of Continuing Liability for postings to other treaty countries.
How long is a certificate of coverage valid?
Validity depends on the underlying agreement. EU A1 certificates run up to 24 months under Article 12 of Regulation 883/2004, while US Certificates of Coverage run for 5 years and can be extended to 8 with mutual consent. Multi-state worker certificates issued under Article 13 are reviewed annually if work patterns change.
What happens if no totalisation agreement exists between the two countries?
The certificate route doesn't apply, and the employer pays social-security contributions in both countries: home rates because the employee stays on home payroll, and host rates because the host country has no obligation to recognise an exemption. Common exposed pairs include US-China, US-India, UK-Brazil, and UK-Mexico. See the totalisation agreement entry for the full list of country pairs.
Does an EOR handle the certificate of coverage application?
Usually no, because EOR providers run host-country payroll while the certificate is a home-country document filed with the home social-security authority before the assignee lands. The EOR will accept and apply the certificate at host payroll, but the application itself sits with the home payroll provider, the home-country NIC team, or a mobility-tax specialist. See the tax equalisation entry for how the certificate sits inside the broader mobility-policy stack.
Can a certificate be issued retroactively?
Retroactive issuance is possible in some country pairs but routinely difficult. The home-country authority will usually issue the certificate from the date of application or the date of departure if the application is filed promptly, while host-country contributions already collected sit in a reclaim queue that can run 12 to 18 months in France or Italy. The reliable rule is to apply before host payroll opens.