Genesis 16:16

And Abram [was] eighty years old when Hagar bare Ishmael to
Abram.
] Which is easily reckoned, for he was seventy five years of age when he left Haran, ( Genesis 12:4 ) ; and he had been ten years in Canaan when Hagar was given him by Sarai for his wife, ( Genesis 16:3 ) ; and so must be then eighty five years of age, and of course must be eighty six when Ishmael was born.