In superscriptions to the biblical prophetic books, dates are usually expressed in terms of the reigns of kings. In the headings to Amos and Jeremiah, however, the standard regnal chronology is augmented by a “nonregnal date” that does not directly refer to a monarch. Amos’s prophecies are set “two years before the earthquake” (Amos 1:1), while Jeremiah’s career ends with “the exiling of Jerusalem in the fifth month” (Jer 1:3). In this article, I examine both of these nonregnal dates and conclude that they serve similar rhetorical purposes in their respective books. Each reference anticipates central themes of divine judgment that are developed across the rest of the book, while also corroborating an important prediction that reinforces the authority of the titular prophet. The nonregnal dates thus help to show how the social processes of “prophetic validation” continued to operate in the literary production of prophetic books. The uniqueness of these dates among the Latter Prophets may be related to the unusually detailed accounts of prophetic conflict found in Amos and, especially, Jeremiah.