Insurance plans sold on Covered California, the state's Obamacare marketplace, will see modest price increases for the upcoming enrollment season.

The plans on average will be 4 percent more expensive during the 2015-2016 enrollment period, slightly lower than last year's 4.2 percent rate hike, state exchange officials announced Monday. Covered California Executive Director Peter Lee credited a successful enrollment season and extra federal dollars for insurers enrolling sicker customers for the lower-than-expected rate increases.

"This is another year of good news for California's consumers and further evidence that the Affordable Care Act is working," Lee said. "Covered California is holding the line on rates and keeping coverage within reach of hundreds of thousands of consumers, while giving them more choices than ever before."

Twelve insurers will offer plans on the state's exchange, including two newly participating insurers: UnitedHealth Group and Oscar Insurance Corp. The exchange started with 13 insurers during the first enrollment season, which began in 2013.

California is the first state to release final exchange rates. When states released proposed rates earlier this year, as required by the healthcare law, some insurers proposed big, double-digit rate hikes, prompting a fresh round of criticism that Obamacare wasn't helping lower healthcare costs. The law doesn't prohibit big rate increases, but it does require that any intended hike above 10 percent be made public ahead of time.

Those earning less than four times the federal poverty level, about $47,000 for an individual and $97,000 for a family of four, can qualify for subsidies under the Affordable Care Act. The next enrollment period begins Nov. 1 and continues through the end of January. California is one of 14 states and the District of Columbia entirely running their own exchanges.