Health Contribution Base: Why You Should Avoid Pro-rating to Prevent URSSAF Risks

When your collective agreement refers to the “fixed gross base salary,” the health contribution is calculated on the contractual salary — and definitely not on the reduced remuneration due to absence. Pro-rating this base means underreporting… and exposing yourself to a potential URSSAF adjustment. Here is the rule and the method for setting it up.

This article is part of the file Payroll Law: The Employer’s Guide.

The Base to Retain: Contractual Fixed Gross Salary

When the collective text refers to the “fixed gross base salary” (a common phrase, for example in certain collective agreements for service providers), the health contribution is calculated on the contractual base salary, regardless of monthly variations.

Example: for a contractual base salary of €4,000 gross, the contribution is calculated on €4,000, even if an absence has brought the paid remuneration down to €3,300 (subject to the collective ceiling, often expressed as a percentage of the tranche A of the monthly ceiling of the Social Security).

Why? The term “fixed” opposes any variation: bonuses, increases, overtime or additional hours, and specific variations due to an absence. The text expressly excludes these accessories (“excluding bonuses, excluding increases…”). A strict interpretation is required: if the social partners had wanted a prorated base, they would have referred to “the remuneration subject to contributions” or a base “prorated in case of absence.” In the absence of such specifications, one does not substitute the fixed gross base salary with the social base of the month.

The URSSAF Risk of a Reduced Base

Taking €3,300 instead of €4,000 leads to underreporting of contributions, both employee and employer to the scheme. However, the employer’s contribution to financing supplementary health insurance constitutes a benefit, a fraction of which is reintegrated into the CSG/CRDS base. A reduced contribution can therefore result in a social loss — and pose a risk of adjustment in case of an audit. Retaining the contractual reference base secures the social treatment.

Caution: check the insurer’s notice or the collective contract — a clause may arrange the calculation in case of suspension of the contract. In the absence of contrary stipulation, calculating based on the non-prorated contractual base salary is the most robust option.

Setting Up Bases: By Collective Agreement

Do not look for a unique “standard” base. The texts can be hybrid (with the same article referring to “salaries subject to contributions” while excluding overtime, bonuses, allowances, in-kind benefits, and professional expenses).

Method: define a reference base (PMSS, gross subject to contributions, or base salary), then apply inclusion/exclusion rules by payroll item, according to the collective agreement, the implementation act, and the insurer’s contract.

Frequently Asked Questions

Pro-rating in case of absence? No, base = contractual base salary.

Why is there a URSSAF risk? Underreporting → impact on CSG/CRDS → possible adjustment.

A base for all collective agreements? No: reference base + rules by item.