French Labour Cost Lab: An Open-Source Dashboard for Simulating Labour Costs, Contribution Reliefs and Socio-Fiscal Marginal Returns in France

This working paper presents the French Labour Cost Lab, an open-source interactive dashboard designed to simulate and visualize the structure of labour costs and socio-fiscal marginal returns in France. The tool queries the public Monentreprise/URSSAF calculation engine over a fine-grained wage grid ranging from 0.8 to 3.5 times the statutory minimum wage (SMIC), with a step of 0.01 SMIC, for a gross monthly SMIC reference of 1,801.80 euros. It produces a comprehensive set of indicators, including gross wage, net wage, total employer cost, employer and employee social contributions, the RGDU 2026 contribution relief amount, the social wedge, effective employer contribution rates, marginal employer-cost indicators, and a reference socio-fiscal return measure incorporating estimated personal income tax and an estimated prime d'activité for a stylized reference household.The dashboard is built around a combinatorial profile architecture defined by employee status, territorial regime and occupational injury risk scenario. Its primary contribution is threefold. First, it enhances the reproducibility of labour cost analysis by relying on a documented, open-source pipeline and a public calculation engine. Second, it provides fine-grained wage-scale granularity, making it possible to detect non-linearities and threshold effects that are not visible in aggregate indicators or isolated case-type calculations. Third, it renders visible the interaction between employer contribution reliefs, employee social contributions, personal income taxation and in-work benefits in shaping the marginal return to gross wage increases.The paper situates the tool within the broader literature on labour cost incidence, distinguishes institutional accounting incidence from economic incidence, documents the construction of the main indicators, and presents internal consistency checks validating the simulated dataset. The French Labour Cost Lab is intended as an open infrastructure for applied economic analysis, policy discussion, pedagogical use and reproducible research. It should not be interpreted as an official payroll calculator or as a full socio-fiscal microsimulation model.