We're less than one week away from the start of open enrollment, the period when Medicare beneficiaries can make important changes to their coverage. If you're already on Medicare, it's important that you seize the opportunity to lower your out-of-pocket healthcare costs in 2021. At the same time, though, make sure you don't fall victim to these myths that could cause you to make some pretty poor choices in the coming weeks.

1. If I keep the same plan, nothing will change

Each year, your Part D or Medicare Advantage plan is required to provide you with a notice of change, and at this point, you should already have access to that document. Your plan will outline the changes in coverage you can expect. While those may end up being minor in nature, they could also be significant.

For example, if you have a Part D drug plan, you may be notified that one of the medications you take has now been grouped into a higher tier, resulting in a much higher copay for you. As such, don't assume that your plan won't change for the worse because it may -- in which case, it could make sense to switch to a different plan while you can.

The word Medicare in chalk on a blackboard with a stethoscope up against it

Image source: Getty Images.

Of course, the opposite could happen, as well -- your Medicare plan might change for the better. If you were thinking of switching plans because you're unhappy with your current coverage, it pays to see if your notice of change has information that sways you to retain the plan you have.

2. If I sign up for Medicare Advantage, my costs will increase

Each Medicare Advantage plan sets its own premiums and comes with its own set of costs you're responsible for. But don't assume that you'll pay more for Medicare Advantage than you will for original Medicare.

Many Advantage plans have a $0 premium, and some plans pay all or a portion of your Part B premium, too. And since Medicare Advantage covers a number of services that original Medicare doesn't, like dental care, vision exams, and hearing aids, you may find that your total costs go down with an Advantage plan, even if your premium costs increase.

3. If I miss open enrollment, I can just make changes later on

If you miss the opportunity to make changes to your coverage during this year's open enrollment period, rest assured that you won't be stuck with your existing Medicare plan for the rest of your life. But you will be stuck with it for another year. As such, if you're thinking of switching plans, be sure to take action at some point between Oct. 15 and Dec. 7.

There is an exception to the above. If you're on Medicare Advantage and want to switch plans, you can do so during the Medicare Advantage open enrollment period, which runs from Jan. 1 through March 31 each year. But during that time, you won't be able to make any changes to your Part D coverage.

Whether you're satisfied with your existing Medicare coverage or not, it pays to research your plan choices during open enrollment. The more digging you do, the more likely you'll be to find the most cost-effective way to cover your healthcare needs and stretch your retirement income further.