Messiah’s Calendar is a calendar proposal that has 20 months of 18 days each grouped into 4 seasons, where the last month of a season is longer: It usually has 19 days, but the last month of winter has 20 days in common and 21 days in leap years. The seasons are roughly aligned to the solstices and equinoxes, with the year (and spring) beginning on the Northern vernal equinox (i.e. around Gregorian 20 March).