If you're a senior, fall probably conjures up images of colored leaves, pumpkin spice, and Medicare open enrollment. Many people sign up for Medicare in conjunction with Social Security; some seniors sign for Medicare beforehand. If you're already on Medicare, open enrollment is your one opportunity to make changes to your health coverage, and it begins in just one month. Now that may seem like plenty of time, but in reality, there's a fair amount of legwork you may need to do to make the most of open enrollment, so it's important that you prepare for it accordingly. Here are five things you should know about this crucial period.

1. Changes to your health coverage won't take effect immediately

The decisions you make during this fall's open enrollment period will impact your Medicare coverage beginning Jan. 1, 2021. Be sure to account for that so your near-term budget isn't thrown off-course.

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2. You can ditch Medicare Advantage if it's not working for you

Many seniors on Medicare sign up for a Medicare Advantage plan rather than stick to original Medicare (meaning, Parts A, B, and D, which cover hospital care, outpatient care, and prescriptions, respectively). Advantage plans tend to pay for a number of key services that original Medicare does not, like dental exams, vision screenings, and hearing aids. But Medicare Advantage could also limit you to a relatively small provider network, and so if your plan isn't working out as well as you thought it would, you can switch over to original Medicare during open enrollment.

3. You can move from original Medicare to Medicare Advantage

Maybe you're unhappy with your coverage under original Medicare -- namely, you're tired of having to pay a fortune every time you go to the dentist. During open enrollment, you can switch from original Medicare to a Medicare Advantage plan that may offer more comprehensive coverage.

4. You can get a new Medicare Advantage plan

Not all Medicare Advantage plans are created equal. Whereas there's a standard monthly premium that applies to Medicare Part B, each Advantage plan has its own costs and benefits. If you're paying too much or aren't happy with your coverage, you can stick with Medicare Advantage but move to a new plan.

5. You can change your Part D drug plan

If you're on Medicare Advantage, that plan should cover your prescription needs. But if you're on original Medicare, you'll need a Part D drug plan. Part D drug plan formularies can change from year to year so that your costs for a certain prescription may rise or fall, even when you stick to the same plan. Be sure to review what your coverage will look like for 2021 under your existing Part D plan and see if there's a more cost-effective alternative you can switch it. Similarly, if you're no longer taking a certain prescription, it pays to see if there's a cheaper plan out there for you.

The changes you make -- or don't make -- during Medicare's open enrollment will impact you throughout 2021, so it's important to take the time to work through your options. Medicare's fall enrollment begins on Oct. 15 and lasts until Dec. 7. Keep in mind, though, that open enrollment is for existing Medicare beneficiaries only. If you missed your initial enrollment window, you'll have to wait until Medicare's general enrollment period to sign up, which runs from Jan. 1 through March 31.