30-40% is typical. Agree with F0nzie. 30% is a high number if the practice has a no show rate of 50% and no no-show policy in place. 40% is a better number if no-show rate is less than 5% and they charge full no-show fees.
Very simple math.
One practice has 25% no-show rate (not uncommon, mind you) and has zero no-show policy. Out of 100 patient hour at $200 per hour, you collect $10,500 while the practice takes $4,500 at 70/30 cut.
Another practice has 5% no-show rate and for each no show, has shown the ability to recover at least $100 out of $200/hour potential fee. Out of 100 patient hour at $200 per hour, you collect $11,700 while the practice takes $7,800 at 60/40 cut.
In the latter practice, both the doctor and the practice win.
I run a tight ship and I would never allow less than 35-40% cut from the owner side of things. I would personally be very wary of practices that offer you 70/30 split because it means a) they accept all comers (both the quality of doctors and quality of patients suffer. they don't pre-screen their patients), b) they run a loose ship, c) they have terrible collection ability (or screw you by not releasing you the exact collection data every month) or d) they have a lot of MediCaid patients.