SPRINGFIELD, Mo. -

Agents at the CoxHealth enrollment center are busy taking calls and meeting with walk-ins.  March 31 is the last day for open enrollment in the federal health care marketplace.

"I will say, if you haven't been on the website up until this point, it will feel very challenging, just because the more people that are on the site, the slower it becomes," said Diane Rozier of Cox.

After March 31, those who are uninsured could end up paying a penalty under the Affordable Care Act, also known as Obamacare. 

Your household size and income help determine which plan is the best fit. 

"You have to determine between groceries and medical bills and clothes and gas and car insurance.  It's, like, what gives?" said Margi Greek of Seymour.

Greek is a single, working mom who recently signed up for insurance through the marketplace.  A newly-diagnosed heart condition meant her private insurance costs more than doubled.  That is why she turned to the health insurance exchange.

"It was at $232 a month, and it skyrocketed to $598," Greek said.

Registering with Obamacare means Greek now pays nothing, thanks to the tax credit.

"The marketplace is a mechanism to purchase private insurance.  The benefit of going through the marketplace is that you can find out if you're eligible for a tax credit," Rozier said.

Not everyone is eligible for a tax credit, and that means insurance can still be costly for some.  That is one reason some people shopping for insurance decide to pay the penalty rather than buy coverage.

Insurance counselors recommend that you try the government website to see if there is a private plan that would work for you.  The site is easier to use in the morning hours, because fewer people are online.

For extra help, you can call the counselors at CoxHealth at (417) 269-2945.  Other health care companies also have navigators who will help you.