Isaac Newton died on March 20, 1727 according to the Old Style (Julian) calendar used in England at the time. However, when converted to the New Style (Gregorian) calendar used internationally, this corresponds to March 31, 1727. The question uses the Gregorian date, which is the internationally recognized standard for historical records. England didn't adopt the Gregorian calendar until 1752, over 25 years after Newton's death.