We are told that God’s word came to the prophet Hosea in the days of Uzziah, Jotham, Ahaz, and Hezekiah, kings of Judah, and in the days of Jeroboam the son of Joash, king of Israel
(Hosea 1:1). Unfortunately this gives us a rough timespan of around 100 years, most of the eighth century BC, because both Uzziah and Jeroboam II’s reigns began in the 790s and Hezekiah died in the 680s BC.1 There are at least two further obstacles to reaching a specific date for Hosea’s ministry:
The reigns of the kings recorded in 1 and 2 Kings often overlap. The end of reigns and beginning of their successor’s reigns is not always clearly defined.
After the kingdom splits (1 Kings 11:1–43), it is not always clear how the respective reigns of northern (Israel) and southern (Judah) kings relate to one another.
Since it is very unlikely Hosea was active as a prophet for close to 100 years, we have to try and pick the period that best fits with his message. Because the capital of Israel (Samaria) was destroyed in 722 BC we can treat that as the most probable end of his prophetic ministry. We can say this because Hosea was almost explicitly concerned with the northern kingdom of Israel. However, his message never shifts its focus to the southern kingdom of Judah.
Most commentators fix the timespan of his ministry between the 750s and 722 BC. As Hubbard notes, this would allow for him being active during the reigns of both Uzziah, also called Azariah (790–740 BC; see 2 Kings 15:1–7) and Jeroboam II (793–745 BC; see 2 Kings 15:8–12).2
1 The word of the LORD that came to Hosea, the son of Beeri, in the days of Uzziah, Jotham, Ahaz, and Hezekiah, kings of Judah, and in the days of Jeroboam the son of Joash, king of Israel.