Basically take the extra social security tax they have to pay, and subtract that from salary (adjust a bit since the lower salary also lowers the tax).
If they cover health insurance then subtract that as well.
> This simply isn't true.
It's lovely hearing that something I've actually experienced is not true.
I switched from contractor with flexible hours, to employee full time (with the same company), and my take home was lower as an employee, but then again I got health insurance.
If I had to do it again I would have stayed a contractor: I made more money, and I could shop around for better health insurance.
The company might have said no and/or given me fewer hours, so I guess that's a negotiation I would have done.
Of course in California the choice would be taken away from me.