Ooooh, that's a bit beyond me, I'm afraid. It depends on the age of the stock, health, the weather, and how randy your roo is!! Also the age of the eggs, the conditions they have been kept in and if they are shipped or not (they may well all be fertile but some won't start, or quit early). The rule of thumb seems to be 50% hatch rate for shipped, and anything at all for collected eggs. Genetics can have a part to play, as there are fatal genes in some breeds, but please please don't ask me what they are!!
How many do you have set and how many days are they incubating?
Please check out the sticky at the top of this board and see the candling pictures, they are really helpful as a guide.