Key Takeaways:

• Original Medicare consists of Part A (hospital insurance) and Part B (medical insurance).

• If you are a U.S. citizen age 65 or older, you are eligible for Original Medicare and usually automatically enrolled the month you turn 65.

• Original Medicare includes out-of-pocket costs including premiums, deductibles, and coinsurance.

• If you aren't automatically enrolled in Original Medicare, the best time to do so is during your Initial Enrollment Period.

Medicare is a complicated program with lots of moving parts, and that makes it tough for even the most knowledgeable consumer to understand. But knowing the ins and outs of Medicare will help you make the right coverage choices for your health — and your wallet. Keep reading to learn more about Original Medicare, what it covers, what it costs, and how to sign up.

What is Original Medicare?

Medicare — the federal healthcare program for people over age 65 or younger people with disabilities —consists of four parts, each covering a different set of healthcare services:

• Part A: Hospital stays and other inpatient care

• Part B: Outpatient medical care (like doctor visits)

• Part C: Medicare Advantage (a separate, optional insurance that replaces Part A and Part B coverage)

• Part D: Prescription drugs, also optional

Established in 1965, Medicare originally consisted of Parts A and B, while Parts C and D were added years later. Now, Parts A and B together are often referred to as Original Medicare.

What Does Original Medicare Cover?

Medicare Parts A and B will cover a good portion of your healthcare costs. Here's a closer look:

There are a number of healthcare services that Medicare doesn't cover. Here's a sample of the most common items Medicare won't pay for:

• Personal care not requiring medical staff

• Doctor appointments based on no specific problem

• Eyeglasses and vision exams

• Hearing aids and exams

• Immunizations (with some exceptions)

• Cosmetic procedures

• Routine dental care and dentures

• Routine or preventive foot care

• Items and services furnished outside the U.S. and its territories

Are You Eligible for Original Medicare?

You are eligible for Original Medicare as long as you are age 65 or older and a U.S. citizen.

If you are under 65 years old with a disability, you may also be eligible for Original Medicare. In that case, you must have received Social Security disability insurance (SSDI) benefits for 24 (non-consecutive) months. You'll become eligible for Original Medicare on the first day of your 25 month of collecting SSDI benefits.

How Much Does Original Medicare Cost?

As an Original Medicare beneficiary, you'll have to pay for portions of your care. The out-of-pocket costs you must pay are:

• Premiums: Monthly fees you pay to keep you enrolled in the program

• Deductibles: An amount you must pay before Medicare coverage kicks in

• Coinsurance: A percentage of your care you pay for after you've met your deductible

What are the Medicare Part A Costs?

Most beneficiaries qualify for premium-free Part A. This is the case if you or your spouse is over age 65 and:

• Receive retirement benefits from Social Security or the Railroad Retirement Board

• Are eligible to receive those retirement benefits but have not yet filed for them

• Had Medicare-covered government employment

If you don't qualify for premium-free Part A, the monthly amount you'll pay in 2020 depends on how long you or your spouse has worked and paid Medicare taxes:

• Less than 7.5 years: $458

• Between 7.5 and 10 years: $252

For each benefit period, you must pay a $1,408 deductible. A benefit period begins the day you're admitted to the hospital as an inpatient, and ends what you haven't received any inpatient care for 60 days in a row.

In addition to your deductible, you must also pay coinsurance during each benefit period, depending on the amount of time you spend in inpatient care:

• Days 1-60: $0

• Days 61-90: $352 per day

For stays beyond 90 days, the cost can add up quickly. Medicare gives you a benefit called "lifetime reserve days." You can receive up to 60 of them over your lifetime, and you can use them to extend your Part A coverage past 90 days for each benefit period. For days 91+ of inpatient care in 2020, you'll pay:

• $704 per day if you use lifetime reserve days

• 100 percent of all costs if you don't use lifetime reserve days

What are the Medicare Part B Costs?

The Part B premium you pay in 2020 depends on your income and how you file your tax return.

The standard part B deductible is $198. After you've met your deductible, you pay 20 percent coinsurance. That means that for any care you receive, Medicare will pay for 80 percent of the cost, and you will pay for 20 percent.

How Do You Sign Up for Original Medicare?

You will be automatically enrolled in Parts A and B on the first day of your 65th birthday month if you have received Social Security retirement benefits for at least four months before you turn 65. You will simply receive your Medicare card in the mail (usually three months before your 65th birthday).

If you will not have received Social Security benefits for at least four months before you turn 65, you must sign up for Medicare Part A and Part B. To do this, you can enroll with Social Security in one of the following ways:

• Online at the Social Security website

• In person at your local Social Security office

• Over the phone by calling 1-800-772-1213 (TTY: 1-800-325-0778)

If you do have to sign up for Medicare, you can do so during one of the following enrollment periods:

Initial Enrollment Period: Your IEP begins three months before the month you turn 65, includes your birthday month, and ends three months after your birthday month.

General Enrollment Period: If you didn't sign up during your IEP, you can sign up during the General Enrollment Period. It runs from January 1st to March 31st each year. But there's a catch: If you sign up during this period, you won't get premium-free Part A (even if you qualify for it), and you'll have to pay the monthly premium.

Original Medicare is a good start at covering your healthcare costs as a senior, but it's just the beginning. Medigap plans, Medicare Advantage, and Medicare Part D are all ways you can add to or supplement your Original Medicare coverage.

If you need additional help understanding your Medicare coverage options, it's worth it to consult a licensed insurance agent who specializes in healthcare.

Andrea Bonner is a healthcare writer with more than 10 years of experience covering senior health. She is from the Raleigh-Durham area in North Carolina.