Not everyone will reach that gap, and people who get government help paying drug plan costs will not face it.
For those who do reach the coverage gap, your 2019 share of brand-name drugs during that period will be 25 percent — which is the same share you pay before reaching the coverage limit — down from 35 percent in 2018. For generics, your out-of-pocket share will be 37 percent, down from 44 percent this year.
Sometimes, you can find medicines at a cheaper cost than through your plan, such as with a free drug-discount card. However, if you go this route instead of through your insurance, your plan won't count the medicine's cost and your copay toward your deductible or other calculations it uses to determine your share, Gavino said.
More from Personal Finance:
Two ways to defray this retirement risk: How to choose what's right for you
How to make the most of Social Security's 2.8% cost-of-living adjustment for 2019
Here are the best and worst states for taxes
She also recommends checking your plan's limits on any medications you know you'll need. Sometimes, they might have a cap on, say, how many pills of a certain medicine they'll pay for in a month.
Another change to be aware of: If you choose an Advantage Plan during fall enrollment and realize afterward that it's not ideal, you can change your coverage between Jan. 1 and March 31. You'll be able to switch to either another Advantage Plan or to original Medicare (Parts A and B) and a stand-alone Part D prescription drug plan.
Basically, this means that the only way to change your drug coverage during that time would be if it was part of an Advantage Plan. So if you choose a stand-alone drug plan in conjunction with original Medicare, you're stuck with it for a year unless you qualify for a special enrollment period (i.e., you move to a different state).