וַתִּכָּנַ֤ע מוֹאָב֙ בַּיּ֣וֹם הַה֔וּא תַּ֖חַת יַ֣ד יִשְׂרָאֵ֑ל וַתִּשְׁקֹ֥ט הָאָ֖רֶץ שְׁמוֹנִ֥ים שָׁנָֽה׃ (ס)
So Moab was subdued that day under the hand of Israel. And the land had rest fourscore years.
Metzudat David on Judges
the end of the eighty years is from the beginning of the subjugation