Sarah was about 90 years old when she gave birth to Isaac, according to the biblical account in Genesis.

In many explanations, you’ll also see it narrowed down as “around 90–91,” because:

  • Genesis states Sarah was 90 when God promised she would bear a son.
  • Isaac’s birth follows that promise shortly afterward, so some writers say she was about 91 at the actual birth.

So, if you’re answering the question “how old was Sarah when Isaac was born,” the commonly accepted answer is that she was 90 years old , with some commentators adding that she may have been about 91 by the time of Isaac’s actual birth.