Ash Wednesday is exactly 46 days before Easter Sunday, a moveable feast based on the cycles of the moon. The earliest date Ash Wednesday can occur is 4 February (which is only possible during a common year with Easter on 22 March), which happened in 1598, 1693, 1761 and 1818 and will next occur in 2285. The latest date Ash Wednesday can occur is 10 March (when Easter Day falls on 25 April) which occurred in 1666, 1734, 1886 and 1943 and will next occur in 2038.