California recently announced a premium rate structure for health plans offered through the state health insurance exchange. The exchange, called Covered California, announced that that 13 insurers will participate although three prominent health insurers — Aetna, Cigna and UnitedHealth — will not participate in the exchange next year.

Covered California primarily will serve individuals and small businesses. Supporters hope that the exchange will function similar to websites like Amazon and Expedia so that users will be able to choose among various health plans through an easily navigable online store. The exchange is expected to open for registration in October, and an estimated five million people will purchase plans through the exchange in 2014.

Exchange officials said that premiums submitted for next year’s individual market ranged from 2% higher to 29% lower than the current average premium for small business plans in the state’s largest metropolitan areas. To help keep premium rates low, participating health plans reduced their profit margins to about 2% or 3% and negotiated lower reimbursements for hospitals and physicians.