One calendar month cancellation period means the contract will end on the last day of the following month.
1 calendar month: it does not matter if you cancel at the start of the month or at the end of the month. The cancellation notice period starts on the 1st of the month following your cancellation. (Example: you cancel on August 3rd -> your cancellation notice starts on September 1st and the contract ends on September 30th).
Notice: monthly membership has a minimal duration of two calendar months. One calendar month notice