When does Medicare open enrollment take place? Here’s what to know when picking your plan.

You may have noticed the increase in TV commercials and flyers in the mail reminding you it’s that time of year again. Nope, not the midterm election. It’s open enrollment period for Medicare plans, running Oct. 15 to Dec. 7. It’s when beneficiaries can switch to a different plan, add prescription benefits or make other changes to their Medicare plans. With hundreds of options to choose from, here’s a rundown of some things to know about Medicare whether you’re signing up for the first time or looking to make a change during open enrollment.

Medicare didn’t used to be so complicated. “The people who talk about Medicare for all are probably not envisioning the system that we have today where private plans have a huge role in the current Medicare program,” said Tricia Neuman, executive director of Kaiser Family Foundation’s Program on Medicare Policy.

Before the rollout of Part D prescription plans in 2006, most retired Americans were enrolled in traditional Medicare, with the option to add on some supplemental plans.

Since then the popularity of Medicare Advantage plans run by private insurance companies has grown significantly. Neuman said about half of all people on Medicare are on Medicare Advantage plans. Consequently, there’s an entire industry of Medicare agents and brokers who help people navigate their options, but who also are making money off selling these private insurance plans.

It’s important to know how they operate. The consumer doesn’t pay for any of these services. But because of affiliations with certain insurance companies, people might not be getting presented with all their options, said Benjamin Link, a pharmacist and vice president of pharmacy for Ohio-based drug analytics firm 3 Axis Advisors.