Medicare Glossary

Benefit Period

This is the way Medicare measures your use of hospital and skilled nursing facility (SNF) services. A benefit period begins the day you’re admitted as an inpatient in a hospital or SNF. It ends when you haven’t received any inpatient hospital care or skilled care in a SNF for 60 days in a row. A new benefit period begins if you go into a hospital or SNF after one benefit period has ended. You must pay the Part A deductible for each benefit period. There’s no limit to the number of benefit periods.


A kind of cost sharing where costs are split on a percentage basis. For example, Medicare Part B pays about 80% of Part B expenses and you pick up the rest.


A kind of cost sharing where you pay a pre-set, fixed amount for each service. Sometimes called "copay."

Cost sharing

Your share for a medical service or supply, including co-payments, co-insurance or deductibles.


A kind of cost sharing where you have to pay a pre-set, fixed amount before Medicare begins to pay for Medicare-approved expenses.

End-Stage Renal Disease (ESRD)

Permanent kidney failure requiring dialysis or a kidney transplant.

Guaranteed Renewable

Medicare supplement plans cannot be terminated by the insurance company unless you make false statements (material misrepresentation) to the insurance company, or don’t pay your premiums on time. Rates are subject to change. Any change will apply to all members of the same class insured under your plan who reside in your state.


This is a joint federal and state program that helps with medical costs for some people with limited income and resources. Medicaid programs vary from state to state, but most health care costs are covered if you qualify for both Medicare and Medicaid.

Medical Underwriting (if your state allows it)

The process that an insurance company uses to decide, based on your medical history: whether or not to accept your application for insurance; whether or not to add a waiting period for pre-existing conditions; and how much to charge you for that insurance.


A health insurance program for people age 65 and over, people under 65 with certain disabilities, and people of any age with End-Stage Renal Disease (ESRD) or Lou Gehrig’s disease.

Medicare Advantage

See Part C.

Medicare Advantage Open Enrollment Period (OEP)

The Medicare Advantage Open Enrollment Period (OEP) will take place from January 1st through March 31st annually. OEP allows individuals enrolled in an MA plan, including newly MA-eligible individuals, to make a one-time election to go to another MA plan or Original Medicare (Parts A and B). Individuals using the OEP to make a change may make a coordinating change to add or drop Part D coverage.

Medicare effective date

When your Part A and Part B benefits become (or will become) active.

Medicare Annual Enrollment Period (AEP)

Each year between October 15th and December 7th there is an Annual Enrollment Period, or AEP, during which you can add, drop, or change Medicare Advantage and prescription drug plans. If you drop your Medicare Advantage plan and go back to Original Medicare, you can apply for a Medicare supplement plan. However, restrictions and/or underwriting for current health status may apply if you are outside of Open Enrollment or Guaranteed Issue Periods. This does not apply to residents of Connecticut and New York where Open Enrollment is ongoing and Medicare supplement plans are guaranteed available.While there are some exceptions, this is generally the only time during the calendar year in which you may opt for different coverage.

Medicare General Enrollment Period (GEP)

If you didn’t enroll in Medicare during an Initial or Special Enrollment Period, the General Enrollment period is another chance to enroll in Medicare Parts A and B. The GEP runs every year from January 1st through March 31st. When you enroll in coverage during this time, it takes effect on the following July 1st.

Medicare Initial Enrollment Period (IEP)

This is the seven-month period during which you become eligible for Medicare. It begins three months before the month of your 65th birthday and ends three months after that month.

Medical Special Enrollment Period (SEP)

In certain situations, you will be eligible to enroll in Medicare, or make changes to your Medicare coverage, without penalty. One Special Enrollment Period applies if you did not enroll in Medicare during your Initial Enrollment Period because you (or your spouse) was still employed and you were covered under a group health insurance plan. In this instance, you will have eight months following the time you (or your employed spouse) stop working or your health coverage ends, whichever comes first. However, you may enroll in Medicare Part B sooner than this to avoid a break in coverage.

Medicare supplement insurance plans

Insurance that you buy from a private insurance company that pays for some of the cost sharing with Medicare Parts A and B coverage. Medicare supplement insurance is available in up to 10 standardized insurance plans. Each plan is named with a letter of the alphabet. There is a high-deductible Plan F option. In Massachusetts, Minnesota and Wisconsin, there are different standardized plan options available.

Medicare Supplement (Medigap) Open Enrollment Period

The six-month period that starts with the first day of the month in which you are both age 65 or older and enrolled in Medicare Part B. If your initial enrollment in Part B is before age 65, you have a second six-month Open Enrollment period beginning the month you turn 65. There may be other situations in which your acceptance may be guaranteed. Enrolling during this period gives you a guaranteed right to buy any Medicare supplement plan sold in your state, regardless of any medical conditions you may have. If you choose to apply outside of your Medicare Supplement Open Enrollment period or a Guaranteed Issue period, you may be underwritten and not accepted into the plan. (This does not apply to residents of Connecticut and New York where guaranteed issue is ongoing and Medicare supplement plans are guaranteed available.)


See Medicare supplement insurance plans.

Modified adjusted gross income

This is your adjusted gross income plus any tax-exempt Social Security, interest, or foreign income you have.

Part A

The part of Medicare that provides help with the cost of inpatient hospital stays, skilled nursing services following a hospital stay, hospice, respite care and some home health services.

Part B

The part of Medicare that provides help with the cost of medically necessary services like doctor services, outpatient care and other medical services Part A doesn't cover.

Part C

Medicare-approved private insurance companies offer plans that provide Medicare Part A and Part B services. Part C plans are also called "Medicare Advantage" plans.

Part D

Plans from Medicare-approved private insurance companies that offer help with the cost of prescription drugs.


A fixed amount you have to pay for an insurance plan; usually as a monthly payment.

Premium Penalty

These may apply to Medicare Parts A and B if you don’t enroll when you’re first eligible, unless you qualify for a Special Enrollment Period.


A person or organization that provides medical services and products, such as a doctor, hospital, pharmacy, laboratory or outpatient clinic.


The basic benefits that make up each Medicare supplement plan. The plans, categorized by letters such as F and N, are standardized from company to company.

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