Each insurance company handles assistant surgery differently. Most however have a fee schedule allowance for the surgical procedure itself. The assistant surgery fee is typically anywhere from 16 to 25% of the surgery fee schedule. So if a fee schedule allowance is $1000 for the surgeon, the assist would be paid at 16%, or $160. So long as your charge for the assistant never dips below the percentage of the surgeon's fee schedule amount, you're fine. I used to import the fee schedule from the insurer into excel and setup a formula to calculate the assist fee. Whenever I noticed our charges dipping below payment, I would recommend increasing the chargemaster for that code.