An estimated 15 million U.S. adults gained health coverage between September 2013 and March 2015, according to the Urban Institute's latest Health Reform Monitoring Survey. The proportion of uninsured working-age adults declined 7.5 percentage points over the period, to 10.1%, the survey estimates. States expanding Medicaid to low-income adults under the Affordable Care Act saw a larger decline than other states. Enrollment in the Affordable Care Act’s new Health Insurance Marketplaces opened in October 2013.