The year-day principle is a crucial element of Adventist interpretation of apocalyptic prophecy. It is particularly important to the understanding of chapter twelve of Revelation. In verses 6 and 14 the woman flees into the wilderness for “1260 days” (12:6, ESV) or “a time, times and half a time” (12:14, NIV). Adventists have understood these two time periods to be the same 1260-year period of Christian history, reckoning a year for each day in the prophecy. Is this principle biblical or is it something made up in order to achieve a particular conclusion? As is so often the case with the Bible, the answer is a little more complicated than the two options above would indicate.
The year-day principle, as expressed by Seventh-day Adventists, usually goes something like this: “In Bible prophecy, whenever a period of time is listed in days, its fulfillment should be counted in years.” The principle as stated is not found anywhere in Scripture. But the Bible paves the way for it by highlighting year-day equivalencies, that days and years can correspond to each other. In Numbers 14:34, for example, the forty years of Israel’s wandering in the wilderness corresponds to the forty days of Israel’s disobedience and rebellion in Numbers, chapters 11-14. In Ezekiel 4:5-6 the prophet is ordered to lie down one day for each year of Israel and Judah’s disobedience. In Leviticus 25 the concept of a week and its Sabbath is extended from days to agricultural years. Daniel 9 contains seventy “weeks” of years. So the sabbatical concept of years corresponding to days of the week highlights year-day thinking in biblical times.
But when should one apply prophetic days as years? There are several guiding principles to consider. 1) Since apocalyptic prophecies, like Daniel 7 and Revelation 12, are full of symbols, a symbolic meaning for any numbers in prophecy should be considered as an option. 2) Year-day numbers tend to be the kind one would not use in normal speech. No parent, for example, would say their child is 1260 days old or even 42 months old, much less 2300 evenings and mornings! Such prophetic numbers are not normal on the face of them. 3) In a sequence of prophetic events, if the prophecy makes more sense when counting the days as years, one should do so. For example, in Daniel 7, the four beasts rule for an average of 250 years each. But when the chief opponent of God appears, getting more attention than all the others, it rules for only three and a half years. Daniel 7 makes more sense historically if the time period is 1260 years. Doing so not only balances the prophecy, but enables it to stretch all the way to the Time of the End.
So is the “year-day principle” principle biblical? Not in an exegetical sense. There is no text in the Bible that states the principle and outlines the contexts in which it is to be applied. The principle was applied to prophetic texts only when the passage of time made such a reading plausible. In other words, while there are plenty of evidences of year-day thinking in the Bible, a prophetic year-day principle was only applied to Scripture when historical circumstances caused such a reading to make sense. For example, the seventy weeks of Daniel 9 seem to point to the Messiah. When the Jews arrived at a point in time 490 years from the beginning of the prophecy, people used year-day thinking to suggest that Messiah was about to come, and from a Christian perspective, he did! Around 1200 AD people began to wonder is a year-day reading of Revelation 12 might point to the time of Jesus’ return. So the principle is not drawn from explicit statements of Scripture, but when prophetic texts were read with the wisdom of time passed, time prophecies of Daniel and Revelation took on new meaning. The year-day principle is a theological principle, not an exegetical one.