Health Contribution Basis: Why Using Pro-Rated Salary Risks URSSAF Scrutiny
When your collective agreement references the “fixed gross base salary,” health contribution is calculated on the contractual salary – and definitely not on the reduced remuneration due to absence. Pro-rating this basis results in under-contribution… exposing you to an URSSAF audit. Here is the rule and method for setting parameters.
This article is part of the file Payroll Law: The Employer’s Guide.
The Basis to Adopt: Contractual Fixed Gross Salary
When the collective text refers to the “fixed gross base salary” (a common wording, for example in certain collective agreements for service providers), the health contribution is calculated on the contractual base salary, regardless of variations within the month.
Example: for a contractual base salary of €4,000 gross, the contribution is calculated on €4,000, even if an absence reduced the remuneration paid to €3,300 (subject to the collective ceiling, often expressed as a percentage of tranche A of the monthly social security ceiling).
Why? The term “fixed” contrasts with any variation: bonuses, increases, overtime or additional hours, and temporary variations due to an absence. The text expressly excludes these accessories (“excluding bonuses, excluding increases…”). A strict interpretation is required: if social partners had intended a prorated base, they would have referred to “remuneration subject to contributions” or a base “prorated in case of absence.” In the absence of such wording, one does not substitute the fixed gross base salary with the social basis for the month.
The URSSAF Risk of a Reduced Base
Retaining €3,300 instead of €4,000 results in a reduced contribution both for the employee and employer to the scheme. Furthermore, the employer’s contribution to the funding of supplementary health insurance constitutes a benefit, a fraction of which is reintegrated into the CSG/CRDS basis. A reduced contribution can thus lead to a social shortfall—and create a risk of audit in case of a check. Retaining the reference contractual basis secures the social treatment.
Caution: check the insurer’s notice or collective contract — a clause may adjust the calculation in case of contract suspension. In the absence of a contrary provision, calculating on the non-prorated contractual base salary is the safest option.
Setting Bases: Collective Agreement by Collective Agreement
Do not look for a unique “standard” base. The texts can be hybrid (the same article may refer to “gross wages subject to contributions” while excluding overtime, bonuses, allowances, benefits in kind, and professional expenses).
Method: define a reference base (PMSS, gross subject to contributions, or base salary), then apply inclusion/exclusion rules by payroll category, according to the collective agreement, the setting act, and the insurer contract.
Frequently Asked Questions
Should contributions be prorated in case of absence? No, the basis = contractual base salary.
Why is there a URSSAF risk? Under-contribution → CSG/CRDS impact → possible audit.
Is there one basis for all collective agreements? No: reference base + rules by category.
Written and supervised by Audrey Mourer, Operational Director and Head of the Payroll Consulting Department at DAIRIA Avocats.
*Also read → The Revamped Payslip 2027 · Overtime: Exemptions