Health Insurance Contribution Base in France: Which Base to Use (and Why Prorating It Exposes You to URSSAF)

When your collective bargaining agreement refers to “basic fixed gross salary,” the health insurance (frais de santé) contribution is calculated on the contractual salary — and definitely not on pay reduced by an absence. Prorating this base means under-contributing… and exposing yourself to an URSSAF reassessment. Here is the rule and the method for setting up your payroll.

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

The base to use: the contractual basic fixed gross salary

When the collective agreement text refers to the “basic fixed gross salary” (a common wording, for example in certain sector-wide collective bargaining 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 reduced the pay actually paid to €3,300 (subject to the contractual ceiling, often expressed as a percentage of band A (tranche A) of the monthly Social Security ceiling).

Why? The term “fixed” excludes any variation: bonuses, premiums, overtime or additional hours, and one-off variations linked to an absence. The text moreover expressly excludes these accessory items (“excluding bonuses, excluding premiums…”). A strict interpretation is required: if the social partners had 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, you do not substitute the month’s social contribution base for the basic fixed gross salary.

The URSSAF risk of an understated base

Using €3,300 instead of €4,000 results in under-contribution to the scheme by both employee and employer. Yet the employer’s contribution to financing supplementary health cover constitutes a benefit, a portion of which is reintegrated into the CSG/CRDS base. An understated contribution can therefore translate into a social security shortfall — and fuel a risk of reassessment in the event of an inspection. Using the contractual reference base secures the social security treatment.

Caveat: check the insurer’s policy 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.

Setting up the contribution 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, gross subject to contributions, or base salary), then apply inclusion / exclusion rules by payroll line item, according to the collective bargaining agreement, the implementing act, and the insurance contract.

Frequently Asked Questions

Prorate in the event of absence? No, base = contractual base salary.

Why an URSSAF risk? Under-contribution → CSG/CRDS impact → possible reassessment.

One base for all CCNs? No: reference base + rules per line item.

Written and supervised by Audrey Mourer, Chief Operating Officer and Head of the Payroll Advisory Division at DAIRIA Avocats.