The legislator adopts various methods to determine the amount of the basis for calculating social security contributions. In the case of employees, it assumes that it is income from employment. In relation to persons conducting non-agricultural business activity, the legislator established the possibility of declaring the amount constituting the basis for calculating social contributions dimension, but it cannot be lower than 60% and not higher than 250% of the projected average monthly salary. ZUS (Social Insurance Institution) has the competence to determine the amount of contributions and their collection. However, in view of the techniques adopted for determining the basis, the pension authority’s competence in checking the amount of the contribution base is different according to the category of the insured.