Every day in the Gregorian calendar can be converted to the Mayan Calendar. The structure of Mayan calendar dates is completely different, but there is an equivalence.
There is a Long Count Mayan calendar that identifies a date by number of days from the Mayan creation (11 August 3114 BC).
In Mayan Calendar a base 20 is used instead of a decimal base. Thus 0.0.0.1.1 0.0.0.2.5 while equals 21 equals 45.