“The lights will go on Oct. 1, but they may flicker,” said Jocelyn Guyer, a director at the Washington-based consultant Manatt Health Solutions. “I worry the most about people making premature judgments on the first couple of weeks.”

The Breakdown

Here’s a primer on what to look for, based on interviews with consultants, insurers, analysts and state and federal officials:

Q: Who runs the exchanges?

Fourteen states have their own on-line exchanges, with the rest run in whole or part by the U.S. government.

Q: Who will use them?

A: The exchanges are open to people who buy coverage on their own and employees of businesses with 50 or fewer workers, as well as those currently shut out of insurance because of cost or a medical condition.

Subsidies are available, on a sliding scale, to those making as much as four times the poverty level, which is $11,500 for a single person and $24,000 for a family of four. Those making less than 138 percent of poverty will be eligible for Medicaid if they live in one of the 26 states set to expand the program.

Sign-Up Numbers

Q: How many people will sign up early on?

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