Biblical Chronology
The following is based on Thiele's book The Mysterious Numbers of the Hebrew Kings.
The chronology of the Hebrew kings rests primarily on a series of reign lengths and cross references within the books of Kings and Chronicles, in which the accession of each king is dated in terms of the reign of his contemporary in either the southern kingdom of Judah or the northern kingdom of Israel. Unfortunately some of these cross references did not seem to match, so that a reign which is said to have lasted for 20 years results in a cross reference that would give a result of either 19 or 21 years.
Thiele noticed that the cross references given during the long reign of King Asa of Judah had a cumulative error of 1 year for each succeeding reign of the kings of Israel: the first cross-reference resulted in an error of 1 year, the second gave an error of 2 years, the third of 3 years and so on. He was able to demonstrate that this was due to two different methods of reckoning regnal years - the accession year method and the non-accession year method.
If we think in terms of our own calendar, if the old king died on December 31 and the new king started to reign on January 1, there was no problem. However if the old king died on December 1, what did you do with the remaining 30 days of the old year? Under the accession year method, those 30 days were called the "Accession year" and Year 1 of the new king's reign began on January 1. Under the non-accession year method the 30 days were Year 1 of the new king and Year 2 began on January 1.
If this were not complicated enough, Thiele was able to demonstrate that the northern kingdom (Israel) celebrated a spring New Year while the southern kingdom (Judah) held to an autumn New Year. Differing new years and different methods of calculating reigns were responsible for much of the confusion in the cross references, with the additional problem that the southern kingdom appears to have adopted its neighbour's non-accession method during the time when Athaliah seized power. Unknown to Thiele when he first published his findings, these same conclusions that the northern kingdom used non-accession years and a spring New Year while the southern kingdom used accession years and a fall New Year had been discovered by V. Coucke of Belgium some years previously, a fact which Thiele acknowledges in his Mysterious Numbers.
With this understanding of chronology, Thiele showed that the 14 years between Ahab and Jehu were really 12 years, which meant that he could date their reigns precisely, for Ahab is mentioned in the Kurk Stele which records the Assyrian advance into Syria/Palestine at the Battle of Qarqar in 853 BC, and Jehu is mentioned on the Black Obelisk of Shalmaneser III paying tribute in 841 BC. As these two events are securely dated by Assyrian chronology at 12 years apart, Ahab must have fought the Assyrians in his last year and Jehu paid tribute in his first year.
Thiele was able to reconcile the Biblical chronological data from the books of Kings and Chronicles with the exception of synchronisms between Hoshea of Israel and Hezekiah of Judah towards the end of the kingdom of Israel and reluctantly concluded that at that point the ancient authors had made a mistake. Subsequent writers have proposed an unattested coregency between Hezekia and his father Ahaz to explain the Hoshea/Hezekiah synchronisms. Among these writers are Thiele’s colleague Siegfried Horn, T. C. Mitchell and Kenneth Kitchen, and Leslie McFall.
Read more about this topic: Edwin R. Thiele