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.

In Christian eschatology, historicism is a method of interpretation of biblical prophecies which associates symbols with historical persons, nations or events. The main primary texts of interest to Christian historicists include apocalyptic literature, such as the Book of Daniel and the Book of Revelation. It sees the prophecies of Daniel as being fulfilled throughout history, extending from the past through the present to the future. It is sometimes called the continuous historical view. Commentators have also applied historicist methods to ancient Jewish history, to the Roman Empire, to Islam, to the Papacy, to the Modern era, and to the end time.