The 44,000 Mainers who now have health insurance under the Affordable Care Act are paying average monthly premiums of just under $100, according to data released Wednesday by the U.S. Department of Health and Human Services.

The cost is that low because nearly nine in 10 Mainers in the federal marketplace receive assistance to pay their premiums. Without the subsidies, the average would be $443.

“The number of people receiving subsidies is significant, but I think that was to be expected,” said Trish Riley, an adjunct professor at the University of Southern Maine’s Muskie School of Public Service who was director of health policy for Gov. John Baldacci. “It’s certainly great news that (health care) is affordable for so many.”

Maine’s average premium of $99 is higher than the national average of $82 after subsidies. Mississippi, at $23 per month, has the lowest average premium. New Jersey, at $148 per month, has the highest.

The variations are attributed to many factors, including market competition, the poverty level in each state, the age of enrollees, and the cost of health care in general.

The percentage of Mainers receiving subsidies, 89, is slightly above the national average of 87 percent.

As of May 1, more than 44,000 Mainers had enrolled in the marketplace, exceeding projections by the Maine Health Access Foundation, a nonprofit company that coordinated the statewide enrollment campaign. Nationally, more than 8 million people have bought coverage through the marketplace.

The first six-month enrollment period ended March 31.

Alyson Cummings with the Maine Health Access Foundation said the latest numbers on premiums could spur more people to sign up in the next enrollment period, starting Nov. 15.

“I think a lot of folks who did not enroll were unsure about how the subsidies would work,” she said. “If you look at the sticker price, it’s like, ‘Wow,’ but now that we see what people are paying, it’s encouraging.”

A major component of the Affordable Care Act, adopted in 2010, was the creation of online health insurance marketplaces to give individuals and families who were uninsured, self-employed, or paying a lot for little coverage a place to shop for more affordable plans. About half of the states, including Maine, decided not to run their own marketplaces. Residents in those states can buy coverage through the federal exchange.

The Affordable Care Act offer credits or subsidies on a sliding scale, based on income, for people who earn as much as 400 percent of the federal poverty level, which is about $79,000 a year for a family of three.

There are several tiers of coverage, including more expensive plans for more comprehensive coverage. There also is wide variation from state to state. “Silver” plans are most similar from state to state, and are the most popular plans.

Mainers with silver plans are paying an average of $87 a month, compared with an average of $69 nationally. The difference comes largely from market competition.

Nationally, each state has an average of five carriers, and some states have as many as 11. Mainers had just two carriers to choose from in the first enrollment period – Anthem Blue Cross Blue Shield and Maine Community Health Options. Harvard Pilgrim Health Care plans to join the marketplace in the enrollment period that starts this fall.

About 80 percent of those who signed up in Maine chose Maine Community Health Options, a new member-owned company. A representative from the insurer did not return calls for comment Wednesday.

Premiums could increase next year for some enrollees. The insurers are seeking increases of 0.1 percent to 3.1 percent, on average. Those requests are subject to state approval.

The Congressional Budget Office estimated in April that the Affordable Care Act would cost $36 billion this year, with about $12 billion of that going to health insurance subsidies.

After the release of the latest statistics, former U.S. Health and Human Services Secretary Kathleen Sebelius said the Affordable Care Act has been a success despite “daunting odds” and a relentless misinformation campaign by critics.

Sebelius said at a panel discussion Tuesday that, despite the law’s success, a “heartbreaking” coverage gap remains in states that have not expanded Medicaid under the Affordable Care Act, including Maine.

Riley, at USM, agreed that while the insurance marketplace provides affordable coverage to many low- to middle-class Mainers, buying a health plan is still not feasible for many.

“Without expanding Medicaid, we’ve left the poorest of the poor with no options,” she said.