A1 certificates for workers posted to Norway

The problem

When a Portuguese company sends workers to Norway, both countries could claim social security contributions on the same wages. Without coordination, the employer would pay both Portuguese Seguranca Social and Norwegian arbeidsgiveravgift — roughly doubling the cost. The A1 certificate solves this by proving which country's system applies.

What an A1 certificate does

It formally certifies that the worker remains subject to the social security legislation of the sending country (e.g., Portugal) during the posting period. Norwegian authorities must accept this — they cannot require Norwegian social security enrollment for a worker with a valid A1.

The financial impact

Without A1: the employer pays Norwegian arbeidsgiveravgift (14.1% of gross salary) and the worker pays trygdeavgift (7.6%). With A1: these are replaced by the home country's rates (Portuguese employer contributions are approximately 23.75%, but the worker avoids Norwegian trygdeavgift entirely). For PAYE workers, the tax withholding rate drops from 25% to 17.4%.

The net saving depends on the rate differential between the two countries. For Portuguese employers posting to Norway, the A1 typically reduces total social security cost because it avoids the double-contribution scenario — even though Portuguese rates are higher than Norwegian employer rates alone.

How to apply

The employer (or worker) applies in the home country's social security institution. For Portugal: Instituto da Seguranca Social (ISS), using form A1 (formerly E101). Required information: worker's identification, employer details, Norwegian client/project details, expected duration, and proof of substantial activity in the home country.

Timing

Apply before deployment. The A1 should be in hand before the worker starts in Norway. Retroactive applications are possible but not guaranteed — and in the interim, Norwegian social security applies by default, meaning the employer must pay Norwegian contributions and then seek refunds if the A1 is eventually granted.

Duration limits

Standard posting: 24 months. Extensions beyond 24 months require an Article 16 agreement between the two countries' competent authorities — these are granted case by case and are not automatic. After 24 months without extension, the worker enters Norwegian social security.

Multi-state workers (working regularly in both countries) follow different rules under Article 13 of Regulation 883/2004 — the applicable legislation depends on where the worker performs a substantial part of activity (25%+ threshold).

Employer obligations with an A1

Keep the original A1 certificate accessible on the work site (Norway) or with the employer's records. Present it to Norwegian authorities on request. Continue paying home-country social security contributions. Report the A1 status correctly in a-melding (this affects which income codes to use and confirms the 17.4% PAYE rate).

What happens without an A1

Norwegian social security applies by default. The employer pays arbeidsgiveravgift, the worker pays trygdeavgift. If an A1 is later obtained retroactively, the employer must apply for a refund of Norwegian contributions — a process that can take months and requires documentation that the home-country contributions were paid for the same period.

Common mistakes

Applying for A1 after the worker has already started in Norway. Assuming the A1 covers longer than 24 months. Not carrying the certificate on site during inspections. Using the wrong a-melding codes (reporting as if A1 exists when it doesn't, or vice versa). Not tracking the 24-month clock across multiple postings of the same worker.