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

This working paper presents the Labor Cost Lab, an open-source comparative ob- servatory that reconstructs how socio-fiscal rules transform an employer cost into a net wage. The project originates in the French Labour Cost Lab (FLCL), a single-country dashboard documented in a first working paper, and generalizes its architecture into a multi-country platform. The Lab now comprises six national modules – France, Germany, Belgium, Switzerland, the Netherlands and the United Kingdom – and a transversal comparison module that places them on a common wage grid expressed in international dollars at purchasing power parity. Each national module follows the same logic: a reference wage grid, an explicit and versioned set of regulatory parameters, a calculation engine, and a harmonized set of outputs covering gross wage, net wage, total employer cost, employee and employer contributions, statutory reliefs, effective rates, socio-fiscal wedges and the marginal return to a gross wage increase. The France module retains the deepest institutional resolution: it queries the public Mon-entreprise/URSSAF engine over a grid running from 0.8 to 6.0 times the statutory minimum wage with a step of 0.01 SMIC, across a combinatorial profile system, and reports the Reduction Generale Degressive Unique (RGDU), a reference socio-fiscal module including estimated personal income tax and estimated prime d'activite, and a family of labour cost efficiency indicators (the FLCL Index). The comparison module does not redefine any national parameter. It converts each harmonized wage point into local currency using the World Bank private- consumption purchasing power parity factor, then calls each national engine directly, without interpolation, for an explicitly documented reference profile per country. Wage points falling below a country's statutory minimum are flagged as hypothetical rather than silently dropped. The contribution of the Lab is fourfold: reproducibility, through documented pipelines, versioned regulatory parameters and open datasets; wage-scale granularity, which exposes non-linearities and threshold effects invisible in aggregate indicators or isolated case-type calculations; visibility of marginal incentives, on both the employer and the employee side; and comparability, through a harmonization protocol that separates what is a genuine institutional difference from what is a currency or pricelevel artefact. The Lab documents accounting and institutional incidence. It does not estimate economic incidence, behavioural responses or employment effects, and it is not an official payroll calculator.