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Quick Guide to Medicare Enrollment

In Triage Health's free Quick Guide to Medicare Enrollment, learn about the four kinds of enrollment periods: initial, general (and late enrollment penalties), special, and open. This Quick Guide also covers evidence of coverage documents.

You have multiple opportunities to sign up or “enroll” in Medicare or change your current Medicare coverage. The four main enrollment periods are the initial enrollment period, a yearly general enrollment period, a yearly open enrollment period, or a special enrollment period.

Medicare coverage is broken up into 4 Parts. There are different enrollment opportunities for each Part of Medicare coverage. For more information about the parts of Medicare coverage, visit the Quick Guide to Medicare – Extended.

Initial Enrollment Period (IEP)

Your first enrollment period for Medicare is your initial enrollment period (IEP). Preparing for your IEP can prevent problems down the line, since signing up for coverage after this period ends can result in penalty fees. You’ll first be eligible for Medicare when:

  • You turn 65. Three months before you turn 65, your seven-month period to choose a Medicare plan begins. You can pick a plan anytime during this period; however, if you would like your coverage to begin when you turn 65, sign up during the 3 months before the month you turn 65. If you wait until the month you turn 65 (or the 3 months after you turn 65) to enroll, your Part B coverage will be delayed. This could cause a gap in your coverage.
  • You have a disability and have received SSDI (Social Security Disability Insurance) for 24 months.


Eligible for an IEPWhen Benefits Begin
65+ receiving SSA Benefits1st day of month you turn 65
Under 65 w/a disability (auto enrolled)After receiving SSDI for 24 months
ALS (auto enrolled)First month disability begins

When people sign up for Medicare, they often get what’s called “Original Medicare,” which refers to Part A & B. Part B is an extra cost, but includes coverage for things besides hospitalization and prescription drugs. If you have other health insurance coverage, you may want to decline Part B, but it is important to understand the rules and weigh your options carefully. Keep in mind:

  • If you or your spouse are still covered through an employer-sponsored plan, ask the employer if they require you to sign up for Part B. If not, you can sign up later without penalty, during a Special Enrollment Period (SEP).
  • If you have TRICARE, you must have Part B. However, if you, your spouse, or your parent (if you are a legal dependent) are an active duty service member, you might not have to get Part B right away.
  • If you have Civilian Health and Medical Program of the VA (CHAMPVA) coverage, you must have Part B.
  • Financial assistance for Marketplace plans ends when you become eligible for Part A.


If you have paid into Medicare through FICA employment taxes, you will likely be automatically enrolled in Medicare Part A. If you want Medicare Parts B, C, or D, or you would like a Medigap plan, you have to choose to enroll in this coverage. If you miss your Medicare IEP, you will pay a late enrollment penalty when you sign up for Part B and Part D.

Enroll in Medicare by contacting Social Security at or 1-800-MEDICARE.

General Enrollment Period (GEP)

If you miss your initial or a special enrollment period, you can also enroll in Medicare during the general enrollment period (GEP). For Parts A and B, the GEP lasts from January 1 to March 31 every year, and your coverage will take effect the month after you enroll. If you want to also pick up a Part D prescription drug plan, the GEP lasts from April 1 to June 30 every year, and your coverage will take effect July 1. If you signed up for Part A and/or B in the GEP, then you can also decide to move to a Part C Medicare Advantage Plan during the GEP that lasts from April 1 to June 30 every year, and your coverage will take effect July 1.

General Enrollment PeriodWhen Benefits BeginWhich Plans
January 1- March 311st day of month following the month you enrollPart A, B, D

Unfortunately, if you enroll in Medicare coverage during a GEP after missing your initial or a special enrollment period, you may have to pay a late enrollment penalty for the rest of your life.

Medicare Late Enrollment Penalties

  • Part A: If you aren’t eligible for premium-free Part A, and you don’t buy it when you’re first eligible, your monthly premium may go up 10% when you decide to enroll. You’ll have to pay the higher premium for twice the number of years you could have had Part A, but didn’t sign up.
    • For example: Charlie only has 30 quarters of eligibility for Part A, but could still get Part A if he paid a monthly premium of $232. He didn’t understand this, so he didn't sign up for 2 years after he was first eligible. He will have to pay a 10% higher premium for Part A, for 2 x 2 years = 4 years.
  • Part B: If you don’t sign up for Part B when you’re first eligible, you may have to pay a lifetime late enrollment penalty for as long as you have Part B. Your monthly premium for Part B may go up 10% for each full 12-month period that you could have had Part B, but didn’t sign up for it.
    • For example: Jed became eligible for Part B on March 1, 2019, but waited to enroll until March 31, 2021, during the General Enrollment Period. His coverage did not begin until July 1, 2021. Jed did not have Part B coverage for 28 months, which is two 12-month periods multiplied by 10%, so he will have a 20% penalty, in addition to his Part B monthly premium, for life!
  • Part C: There is no late enrollment penalty for Part C.
  • Part D: The Part D late enrollment penalty also depends on how long you waited to enroll. Medicare calculates the penalty by multiplying 1% of the “national base beneficiary premium” ($33.06 in 2021) by the number of months you did not have Part D coverage. Then, Medicare rounds this penalty to the nearest $.10.
    • For example: Ainsley did not have Part D or creditable prescription drug coverage for 14 months after her Initial Enrollment Period. Her Part D penalty will be calculated in the following way:
      • $33.06 (2021 base beneficiary premium) x 1% = .3306
      • .3306 x 14 months = $4.6284
      • $4.62 rounded to the nearest $.10 = $4.60
      • $4.60 would be added to her monthly Part D premium for as long as she has Medicare Part D


Each year she will pay an additional ~$55 in Part D penalties. 15 years = $825 in penalties.

Special Enrollment Period (SEP)

Usually, if you decide not to enroll in Medicare during your IEP, you may have to pay a penalty when you enroll later. In some cases, you may qualify for a special enrollment period, or SEP, to avoid paying the penalty for late enrollment. These are times when you may qualify for a SEP for your Part C or Part D Plan

  • Moving: If you move somewhere outside of your current Medicare plan’s service area, move to a place offering new plans, move back to the United States after living in another country, transition in or out of an institution (like a long-term care hospital), or are released from jail, you may qualify for a SEP.
  • Losing Your Current Coverage: You may qualify for a SEP if you lose an employer-sponsored plan, COBRA, Medicaid, or other forms of comparable coverage.
  • New Coverage Opportunities: If you are offered other coverage through an employer or union, enroll in prescription drug coverage comparable to Medicare, or enroll in PACE (Program of All-Inclusive Care for the Elderly) you may qualify for a SEP.
  • Contract Changes: If your plan changes its contract with Medicare you may qualify for a SEP. Qualifying changes include ending your plan, or not renewing your Part C or Part D Plan.


Complete list of situations that would qualify you for a Part C or Part D SEP 

SEPs can vary by the type of coverage you would like to enroll in:

  • Parts A & B: You must work for an employer with 20 or more employees and have health insurance through your job, union, or your spouse’s job. You can apply for Parts A & B any time you’re still covered by the work-related plan, and during the 8 months after your coverage or employment (or spouse’s employment) ends. Beginning in 2023, there is a new Part B SEP for certain exceptional circumstances.
  • Part C: You can sign up for a Part C plan with a SEP during the 63 days after your employer or union health plan coverage ends, or when your employment ends, whichever comes first. Also, the first time you enroll in a Part C plan, you get a Part C “Trial Period” special enrollment period. You have up to 12 months to change your mind and switch to Original Medicare (Parts A & B), and then you’ll be eligible to buy a Part D plan and a guaranteed issue Medigap plan without, going through medical underwriting or facing a pre-existing condition exclusion period.
  • Part D: You can enroll in Part D during the 63 days after your coverage through an employer or union ends.
  • Parts C & D: If your life circumstances change, you could be eligible for an additional SEP for Part C & D. For example, you may be eligible for a Part D SEP if you move out of the service area for your current Part D plan, or enter a long-term care facility.
  • Medigap Plans: Your first chance to buy a Medigap policy is during your 6-month Medigap initial enrollment period, which starts the month you’re 65 and have Part B. During that time, you can buy any Medigap policy sold in your state, even if you have health problems. After that time, you may not be able to buy a Medigap policy, or it may cost more due to past or current health problems. There are some exceptions when you may have special enrollment periods for Medigap.


Generally, changes made during SEPs are effective the first day of the month following the month you choose your plan, if you choose your plan between the 1st and 15th. If you wait until the 16th or later in the month, your plan will take effect the first day of the second following month.

Special Enrollment PeriodWhich Plans
8 months after your retirement or EGHP coverage endsPart A & B, Part C or D
6 months after your Part B effective dateMedigap

Open Enrollment Period (OEP)

During the OEP, you can check to make sure that your current Medicare coverage still works for you and compare your options. The OEP runs from October 15 to December 7, each year. You should consider your prescription drug costs, monthly premiums, “network” (or covered doctors, hospitals, and pharmacies), and “formulary” (list of covered drugs) when comparing plans.

Changes that you can make during the OEP, include:

  • Switching from Original Medicare to a Medicare Advantage plan
  • Switching from a Medicare Advantage plan to Original Medicare; and add a Medicare Part D plan and/or Medigap plan (but you may face medical underwriting when applying for the Medigap plan). For more information, see the Quick Guide to Medigap Plans.
  • Switching from one Medicare Advantage plan to another plan.
  • Switching from one Medicare Part D prescription drug plan to another plan.

Changes made to your coverage during the OEP will take effect January 1 of the new year.

Open Enrollment PeriodWhen Benefits BeginWhich Plans
October 15- December 7January 1Part A & B, Part C, Part D

Evidence of Coverage Documents (EOCs)

If you are enrolled in Medicare coverage, you should receive an “evidence of coverage” (EOC) document each year. The EOC is an important document to help you understand your Medicare plan. It provides an overview of your current coverage, including what your plan covers and how much you pay. Usually, this document arrives during the fall, so you can use it to prepare for the open enrollment period beginning October 15.

More Medicare Resources

For more information on Medicare options, enrollment periods, late enrollment penalties, and how Medicare interacts with other types of health insurance coverage:

Learn More

For more information  visit

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Last reviewed for updates: 01/2022

Disclaimer: This handout is intended to provide general information on the topics presented. It is provided with the understanding that Triage Cancer is not engaged in rendering any legal, medical, or professional services by its publication or distribution. Although this content was reviewed by a professional, it should not be used as a substitute for professional services. © Triage Cancer 2023