Under the ACA, when the insurance company pays a hospital (or any other medical provider) $200, it is allowed to spend $50 (less for larger programs) on salaries and profits and other expenses.
If it gets $300 of premiums and only spends $200 on medical care, it has to send the extra $50 back to the customers (larger programs have to send back $65).
More here:
http://kff.org/health-reform/perspective/beyond-rebates-how-...