Abstract: This article presents a series of theoretical and practical concepts regarding the social security contribution owed by natural persons that obtain revenues from independent activities (production, retail, rendering of services, liberal professions). Throughout the year 2021, tax payers carry out the evaluation in order to establish a potential payment obligation of this contribution, and the completion of the revenues earned, which is the base of establishing the final obligation regarding CAS, will be carried out in the next year, by filling Chapter I of the single tax return. The annual base for the calculation of the social security contribution cannot be lower than the level of 12 gross national minimum wages effective at the date when the single tax return is filled.