Boy thats a tough question, there are many variables to consider.
Are you talking about chicken eggs or quail, etc. I get a better hatch percentage with chickens than with all other birds I have. My last hatch was 93% but sometimes I get around 50%. Your hen to rooster ratio influnces the rate aside from all the incubator variables, at what temperature were the eggs gathered and what temp were the eggs held at before placing in the bator, on and on.