The earliest possible date on which Memorial Day can fall under the U.S. holiday rule is May 25.
Federal law places Memorial Day on the last Monday in May. Because Monday can occur as early as May 25 in that month, the holiday cannot arrive before that date. It can occur as late as May 31, depending on the calendar.
Congress moved Memorial Day from a fixed May 30 observance to the last Monday in May through the Uniform Monday Holiday Act. The Monday schedule took effect in 1971 and created a three-day federal holiday weekend. The rule is sometimes confused with the separate dates used by individual states for Confederate commemorations or local memorial events.
Memorial Day’s calendar position also explains why its date changes every year even though its weekday does not. The holiday always falls on Monday, but its numerical date ranges from May 25 through May 31.