In order to apply the 90 days / 180-day rule, a calculator has been developed for the general public and for the Member States' authorities. The calculator is a helping tool only; it does not constitute a right to stay for a period resulting from its calculation. It is always for the Member States' competent authorities (in particular for the border guards) to implement the provisions and make a decision on the length of the authorised stay or on the overstay.