Health plans participating in Medicare Advantage, the private insurance option for Medicare beneficiaries, have long been paid considerably more to provide coverage of hospital and physician services than what the government spends to deliver the same benefits to enrollees in traditional Medicare. Under the Affordable Care Act, overpayments to these plans are gradually being pared back. But will private plans be able to cope with the reduced payments? Using newly available government data, Marsha Gold, a senior fellow with Mathematica Policy Research, investigates this issue by examining average costs among Medicare Advantage plans and variation in costs among plan types.