Obamacare’s health insurance marketplaces, the law’s public face, go live in one week. Many uninsured Americans will be able to log onto a website, enter some basic information and apply for private health coverage. When the law was written, some of them would have found out they qualified for Medicaid after the program was expanded nationwide.

But because the U.S. Supreme Court made the Medicaid expansion optional last year and more than 20 GOP-controlled states refused to expand the program, millions of poor and uninsured Americans will log onto the marketplaces in the coming months and find out they won’t be able to get health insurance after all.

And those who can might be paying a little more.The fact is, it’s the poorest people who will be the worst off. Obamacare expanded Medicaid eligibility up to 138 percent of the federal poverty level. But a kink in the law also started eligibility for premium tax credits to purchase private coverage at 100 percent of the poverty level.

So in non-expanding states, people above the poverty level will still get federal help for private insurance. But people actually in poverty won’t get any coverage at all.

The final tally on Medicaid expansion is, according to the non-partisan Kaiser Family Foundation: 26 states have accepted it, 22 states refused it and three are still debating. Finalized estimates haven’t yet been released, but a recent Kaiser report estimated up to 6.4 million people will be left uninsured because states declined to expand the program and accept the 100 percent federal funding that came with it.

Not only are fewer people going to be covered in those states, but others might end up paying more for their coverage. That was the finding of a study released recently by RAND, which looked at Florida, Louisiana, and Texas. The population purchasing health coverage on the marketplaces will likely be less healthy without expansion, according to the study.

So for people making between 100 to 138 percent of the poverty level, the people who would have been covered by Medicaid but will now go to the marketplaces, their standard premium could increase by 8 to 10 percent, RAND estimated.

But the Oct. 1 marketplace launch still means people are going to start buying coverage through Obamacare. The Huffington Post detailed the transition Monday.

Most Americans — the 171 million with employer-based coverage and 102 million with existing government-based coverage — won’t see any change at all. About seven million will purchase private coverage on the marketplaces, and nine million will be covered by Medicaid.

Coverage through both private insurance and Medicaid starts Jan. 1, 2014.

The Kaiser estimates on Medicaid expansion are below.

Kaiser Medicaid Expansion Analysis by tpmdocs