Public business incubators are services placed at the disposal of original, generally newly-created projects, to which physical accompaniment, supervision, and location are offered at prices below market value. They have as their aim to help set in motion and consolidate these firms during the stages in which they are weaker. The ultimate goal consists in favouring the generation of innovative firms, inducers of high-quality jobs, which can diversify the local business fabric, thus becoming a key tool in local development.The present paper provides a methodology to study the economic -but above all social-impact of business incubators, based on the examination of 40 from the 42 incubators existing in the Valencian Community (a Spanish autonomous region with five million inhabitants). Data analysis allows us to state that, although business incubators are not economically profitable since they need financial aids and public investment to start operating, they do have social profitability, insofar as the activity developed by entrepreneurs permits to provide public administrations -via taxes-with returns exceeding what was invested in these incubators. It has been determined that 2.8 euros (which can be applied to a variety of social areas) are collected via taxes for each euro spent to start them up.