We calibrate a key parameter of growth accounting—the IT capital elasticity of production—by using the share of returns to IT capital in value added (Mairesse, Cette, and Kocoglu, 2000). The goal of our paper is to estimate this vital parameter econometrically. For our purpose, we use a very rich set of French business data compiled from standard corporate income tax returns (Bénéfices Réels Normaux) and employers’ annual declarations of payroll data (Déclarations Annuelles de Données Sociales). Among other things, these data provide information on the stock of tangible fixed assets in the office equipment, furniture, and IT categories. We developed our measure of IT capital from this fixed-asset item. Our results suggest an IT capital elasticity of production of 0.9%, substantially above the 0.5% share of return on IT capital in production. Various robustness tests corroborate this result, which seems due to the likely existence of excess return on IT capital—a quantity that cannot be measured with the traditional growth-accounting method. Using our elasticity measure, we estimate the aggregate contribution of IT capital to value-added growth at about 0.7 percentage points.