The analysis finds that people who switched from traditional Medicare to Medicare Advantage in 2016 had health spending in 2015 that was $1,253 less, on average, than the average spending for beneficiaries who remained in traditional Medicare (after adjusting for health risk). The findings suggest that the current payment method may systematically overestimate expected costs of Medicare Advantage enrollees. Adjusting payments to reflect Medicare Advantage enrollees’ prior use of health services could potentially lower total Medicare spending by billions of dollars over a decade.