Health Insurance Contribution Base in France: Which Salary to Use (and Why Prorating Exposes You to URSSAF)
When your collective bargaining agreement refers to the “fixed gross base salary,” the health insurance (“frais de santé”) contribution is calculated on the contractual salary — and never on the pay reduced by an absence. Prorating this base means under-contributing… and exposing yourself to an URSSAF reassessment. Here is the rule and the configuration method.
This article is part of the file Payroll Law: The Employer’s Guide.
The Base to Use: The Contractual Fixed Gross Base Salary
Where the collective agreement (“convention collective”) refers to the “fixed gross base salary” (a common wording, for example in certain sector-wide agreements (“CCN”, conventions collectives nationales) for service providers), the health insurance 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 reduced the pay actually paid to €3,300 (subject to the contractual ceiling, often expressed as a percentage of Band A of the monthly Social Security ceiling).
Why? The term “fixed” excludes any variation: bonuses, premiums, overtime or additional hours, and occasional variations linked to an absence. The wording indeed expressly excludes these ancillary items (“excluding bonuses, excluding premiums…”). A strict interpretation is required: had the social partners intended a prorated base, they would have referred to “remuneration subject to contributions” or a base “prorated in the event of absence.” Absent such wording, the month’s social contribution base cannot be substituted for the fixed gross base salary.
The URSSAF Risk of a Reduced Base
Using €3,300 instead of €4,000 results in under-contribution to the scheme, both employee and employer contributions. Yet the employer contribution to the funding of the supplementary health cover constitutes a benefit, a portion of which is reintegrated into the CSG/CRDS base. A reduced contribution may therefore translate into a social security shortfall — and fuel a reassessment risk in the event of an inspection. Using the contractual reference base secures the social security treatment.
Caveat: check the insurer’s notice or the group contract — a clause may adjust the calculation in the event of suspension of the employment contract. Absent any provision to the contrary, calculating on the non-prorated contractual base salary is the most robust option.
Configuring the Bases: CCN by CCN
Do not look for a single “standard” base. The texts may be hybrid (a single article referring to “gross salaries subject to contributions” while excluding overtime, bonuses, allowances, benefits in kind and professional expenses).
Method: define a reference base (PMSS — monthly Social Security ceiling, gross subject to contributions, or base salary), then apply inclusion / exclusion rules by payroll line item, according to the collective agreement, the implementing act, and the insurance contract.
Frequently Asked Questions
Prorate in the event of an absence? No, the base = the contractual base salary.
Why an URSSAF risk? Under-contribution → CSG/CRDS impact → possible reassessment.
One base for all CCNs? No: a reference base + rules by line item.
Written and supervised by Audrey Mourer, Chief Operating Officer and Head of the Payroll Advisory Department at DAIRIA Avocats.
Further reading → The Revamped 2027 Payslip · Overtime: Exemptions