The Millerites were the followers of the teachings of William Miller, who in 1831 first shared publicly his belief that the Second Advent of Jesus Christ would occur in roughly the year 1843–1844. Coming during the Second Great Awakening, his teachings were spread widely and grew in popularity, which led to the event known as the Great Disappointment.

The day-year principle or year-for-a-day principle is a method of interpretation of Bible prophecy in which the word day in prophecy is considered to be symbolic of a year of actual time. It was the method used by most of the Reformers, and is used principally by the historicist school of prophetic interpretation. It is held by the Seventh-day Adventist Church, Jehovah's Witnesses, and the Christadelphians. The day-year principle is also used by the Baháʼí Faith, as well with by most all astrologers who employ the "Secondary Progression" theory, aka the day-for-a-year theory, wherein the planets are moved forwards in the table of planetary motion a day for each year of life or fraction thereof. The astrologers say that the four seasons of the year are directly spiritually, phenomenologically like the four "seasons" of the day.