Factbox: Obamacare case focuses on tax subsidies, insurance exchanges

(Reuters) - The U.S. Supreme Court is set to hear a second major challenge to President Barack Obama's healthcare law on Wednesday, focusing on the issue of tax subsidies available through insurance exchanges set up under the statute. Here is a look at the exchanges and subsidies. HEALTH INSURANCE EXCHANGES The Affordable Care Act, often called Obamacare, requires people who do not get health insurance through their employer, or the government programs Medicare and Medicaid to buy their own insurance. To make that easier, it created health insurance exchanges, which are centralized online marketplaces that allow consumers to shop among competing insurance plans. WHO RUNS THE EXCHANGES? The law requires states to establish their own exchanges, but it allows the federal government to do so instead when states are unwilling or unable. So far, 13 of the 50 states as well as the District of Columbia have established their own exchanges, and another three have state-federal hybrid exchanges, according to the U.S. government's brief in the case. SUBSIDIES Because of the high cost of health insurance, the exchanges depend upon another key part of the law: subsidies. The federal government gives people who buy insurance on the exchanges subsidies in the form of tax credits. The subsidies are meant to help low- and middle-income Americans buy health insurance on the exchanges, and are based on income. For example, a family of four may qualify for subsidies in 2015 if its estimated income for the year is less than $95,400. HOW MANY QUALIFY FOR SUBSIDIES? The U.S. Department of Health and Human Services said that of the people who bought insurance through the federal government's health exchange website as of Jan. 30, nearly nine in 10 qualified for subsidies. On average, the department said, those subsidies covered 72 percent of their premiums, or $268 per month. Wednesday's arguments before the Supreme Court focus upon whether people who buy insurance through federal exchanges can get subsidies. (Compiled by Brendan Pierson; Editing by Will Dunham)