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If you're on Medicare, it's time to give your coverage a yearly checkup. The program's annual enrollment period runs from Oct. 15 through Dec. 7, which is when you can make coverage changes that will take effect Jan. 1. During this autumn window, you can: • Switch to an Advantage Plan (Part C) from original Medicare (Part A hospital coverage and Part B outpatient coverage);

• Switch to original Medicare from an Advantage Plan;

• Move from one Advantage Plan to another;

• Move from one prescription drug plan (Part D) to another, or purchase one if you did not when first eligible. Experts say that even if you've been happy with your coverage, plans are continually modified, which makes it important to evaluate whether your current insurance is still the best option available. "Plans might change what medications are covered," said Elizabeth Gavino, founder of Lewin & Gavino in New York and an independent broker and general agent for Medicare plans. "Same with doctors — they might not still be considered in-network next year. "There also could be new plans in your area that are better than your current one," she said. "It's always important to review your options." It's worth noting that Medicare's fall open enrollment is different from your initial enrollment period, which is a seven-month window that starts three months before your 65th birthday and ends three months after your birth month. Generally speaking, everyone turning 65 must sign up for Medicare Parts A and — unless they meet certain exclusions — Part B during their initial enrollment period, or face a potential penalty. Also during that initial sign-up time, you can sign up for an Advantage Plan, which includes Parts A and B and, typically, a Part D prescription plan. They also often include additional coverage such as dental, vision or wellness programs. Separate rules apply for people who want a supplemental Medigap policy, which can only be paired with original Medicare. And while prescription drug coverage is optional, if you don't sign up when you first qualify for coverage and then change your mind later, you'll pay a life-lasting penalty unless you meet certain exclusions (i.e., you receive acceptable coverage through a union or employer). Here are some key things to keep in mind this year as you review your coverage. If, after evaluating your options, you determine that you want to stick with your current plan, you don't need to take any action.

New for 2019

If you pick an Advantage Plan during fall enrollment and realize afterward that it's not a good fit, you can make a change to your coverage between Jan. 1 and March 31. You'll be able to switch to either another Advantage Plan or to original Medicare and a stand-alone prescription plan. This is a change from the previous rule, which allowed you to switch from an Advantage Plan to original Medicare during a short early year window but didn't allow you to move from one Advantage Plan to another. "There could be circumstances like not knowing at the time you chose the plan that you'd need to see a specific doctor, and you discover in January that the doctor doesn't take your insurance," Gavino said. Be aware that while you can change your mind about your coverage several times during the fall open enrollment period, Gavino said, you can only make one change during the January-through-March window.

Also new next year: If you receive both Medicare and Medicaid — i.e., you are dually eligible — you will only be able to make one change during each of the first three quarters of the year instead of monthly, as previously was allowed. Another change applies to Part D drug plans: As of next year, people with high prescription costs no longer will be exposed to a coverage gap sometimes called the "donut hole." Basically, this is the 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 would kick in and your share of the costs drops. Enrollees' share during that "donut hole" has been dropping over time from 100 percent. In a nutshell: Beginning next year, your share of brand-name drugs during that coverage gap will be 25 percent in 2019, down from 35 percent this year. For generics, your out-of-pocket share will be 37 percent, down from 44 percent in 2018. Additionally, monthly premiums for Part D prescription plans will be lower on average, according to the Centers for Medicare and Medicaid Services, falling to $32.50 in 2019 from $33.59 this year. However, high earners will pay more in 2019 for both Part D and Part B premiums. 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.

What else might change

It's common for both Advantage Plans and prescription drug plans to change the specifics of their coverage from year to year. Modifications to your Advantage Plan could affect aspects such as your premiums, deductibles, copays, covered services, participating doctors and, assuming it comes with prescription drug coverage, which drugs are included on its formulary and what their costs are. Same for the stand-alone Part D prescription drug plans. Either way, you can check medication prices through the government's Medicare Plan finder. There can be broad variations in pricing and limits among plans, so make sure to comparison-shop. More from Personal Finance:

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These donors do charitable giving better — here's what you can learn from them "Make sure your medications are on your plan's formulary and look at what the quantity limits are," Gavino said. "Each carrier has their own limits and it might be less than what you need — say they only allow 30 pills monthly, but you need 60." To make sure your doctor, hospital or other provider still participates in your plan, you have to check with the insurance company that offers it. You can either visit the provider's website or call. If you work with a Medicare agent, that person should be able to help you figure out what coverage is best for your personal situation. And, Gavino said, make sure the agent includes all plans available to you when evaluating your options — not just the policies they sell.

Watch for fraud

Also new: Medicare ID cards. If you haven't received yours yet, it should arrive by April 2019 as long as the Social Security Administration has your current address on file. Instead of your new card bearing your Social Security number — which scammers can use to commit fraud — it includes your new ID number, which is randomly assigned and unique to you.

Source: Centers for Medicare & Medicaid Services