Midrasch zu Haggai 1:1

And to teach that we count (the years) from the exodus from Egypt, it being written "in the second year after their going out from the land of Egypt." When they came to the land, they began to count (shemitah, etc.) from their coming, as it is written (Vayikra 25:2) "When you come to the land, etc." When the Temple was built, they began to count from its building, viz. (I Kings 9:10) "And it was at the end of twenty years from Solomon's building, etc." When the Temple was destroyed, they began to count from its destruction, viz. (Ezekiel 40:1) "… in the fourteenth year of the city's being smitten." When the captivity intensified, they began to count from the captivity, viz. (Daniel 2:1) "And in the second year of the reign of Nevuchadnezzar, etc.", and (Chaggai 1:1) "And in the second year of King Darius, etc." And just as they counted for years, so they counted for months (e.g., [Shemot 19:1]) "In the third month of the exodus of the children of Israel from the land of Egypt."