Retirees who don't evaluate their prescription drug coverage during Medicare's annual enrollment period could end up regretting it. While some Medicare beneficiaries should see the cost of their Part D drug plan drop in 2019, and the coverage gap known as the "donut hole" also will disappear, experts say that assuming your current plan is still your best option could result in unexpected out-of-pocket costs. "Plans might change what medicines they cover, adding or taking out medicines or changing costs," said Elizabeth Gavino, founder of Lewin & Gavino in New York and an independent broker and general agent for Medicare plans.

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For example, Gavino has a client whose 2018 Part D costs were $305, including his premiums and copays. For 2019, if the client were to remain with his plan — with no change in the medicine he takes — his out-of-pocket cost would jump to $2,033. More than 80 percent of people age 65 and older take at least two prescription drugs and more than 50 percent take four or more, according to a 2016 AARP online survey of more than 1,800 adults age 50 or older. Getting prescription drug coverage through Medicare is optional. You can get it as a stand-alone Part D plan that serves as a supplement to original Medicare (Parts A and B) or as part of a Medicare Advantage Plan (Part C). However, if you fail to sign up when you first qualify for coverage at age 65 and change your mind later, you'll face a life-lasting penalty unless you meet certain exclusions (i.e., you receive acceptable coverage through a union or employer). For 2019, Medicare enrollees will have more Part D options, according to new research from the Kaiser Family Foundation. The average recipient will be able to choose from 27 stand-alone drug plans and 21 Advantage Plans that include the coverage.

The report also notes that while some people could see lower premiums and cost-sharing if they don't switch plans, others will see an increase. The Senior Citizens League, an advocacy group, recently released its annual comparison of prices of the top 10 most-prescribed drugs among available plans in one ZIP code. The difference between the lowest- and highest-cost for some of the drugs exceeded $1,000, with one pushing nearly $2,000. "There can be huge variations in the costs," said Mary Johnson, a policy analyst for The Senior Citizens League and author of the pricing study. "It varies depending on the area, but it's a common experience around the country." You can compare medication prices through the government's Medicare Plan finder. Johnson also said the price of a specific drug shouldn't be the only thing you look at. "Sometimes the lowest price on the drug isn't necessarily the better deal," Johnson said. "You need to factor in the cost of the premium as well." Monthly premiums for Part D coverage will be lower on average, falling to $32.50 in 2019 from $33.59 this year, according to the Centers for Medicare and Medicaid Services.

Medicare Part D costs for 2019 Individual tax return* Joint tax return* Married filing separately* You pay $85,000 or less $170,000 or less $85,000 or less Your plan premium Above $85,000 up to $107,000 $170,000 up to $214,000 Not applicable $12.40 + your plan premium Above $107,000 up to $133,500 Above $214,000 up to $267,000 Not applicable $31.90 + your plan premium Above $133,500 up to $160,000 Above $267,000 up to $320,000 Not applicable $51.40 + your plan premium Above $160,000 and less than $500,000 Above $320,000 and less than $750,000 Above $85,000 and less than $415,000 $70.90 + your plan premium $500,000 or above $750,000 and above $415,000 and above $77.40 + your plan premium

However, high earners will pay more in 2019 for Part D and Part B premiums than they did this year. Those with incomes of $500,000 or more ($750,000 for couples) will pay surcharges that result in paying 85 percent of the cost, up from 80 percent in 2018. For stand-alone Part D plans, the average 2019 premium is anticipated to be $41.21, just 2 percent above the 2018 average cost, according to the Kaiser Family Foundation. The amount is higher than the government's estimate because it excludes coverage through Advantage plans and is based on September data versus assumptions about 2019 enrollment that the government uses. Additionally, the standard deductible for Part D plans will be $415 for 2019, up from $405 this year. However, some plans have lower deductibles. There's also good news for Medicare beneficiaries with high prescription drug costs. As of next year, they will no longer be exposed to the donut hole. This is the coverage gap between your drug plan's coverage limit ($3,820 for 2019) and your out-of-pocket maximum ($5,100 for 2019). At that point, catastrophic coverage kicks in and your share of the cost drops.