Medicare Abbreviation List: Parts, Plans, Enrollment, and Costs

Medicare relies on a dense set of abbreviations for its coverage parts, plan types, enrollment windows, income surcharges, and assistance programs. This guide to Medicare abbreviations defines each one you’re likely to see on a plan document, enrollment form, or bill, grouped by category and updated with 2026 figures.

The Four Parts of Medicare

Medicare’s core structure breaks into four lettered parts, each covering a different category of care.

Part A (Hospital Insurance) covers inpatient hospital stays, care in a skilled nursing facility after a qualifying hospital stay, hospice care, and some home health services.¹ Most people pay no premium for Part A because they or a spouse paid Medicare taxes for at least 10 years. If you don’t qualify for premium-free Part A, the full monthly premium is $565 in 2026, and the Part A inpatient hospital deductible is $1,736 per benefit period.²

Part B (Medical Insurance) covers doctor visits, outpatient care, preventive services, and durable medical equipment.³ The standard monthly Part B premium in 2026 is $202.90, with an annual deductible of $283.² Higher earners pay more through an income-based surcharge (see IRMAA below).

Part C (Medicare Advantage, or MA) is an alternative way to get your Part A and Part B benefits through a private insurance company approved by Medicare.⁴ These bundled plans usually include drug coverage and often add dental, vision, or hearing benefits that Original Medicare doesn’t cover. You still pay your Part B premium on top of whatever the MA plan charges.⁵

Part D (Prescription Drug Coverage) helps pay for outpatient prescription medications.⁶ You can get drug coverage through a stand-alone plan paired with Original Medicare, or through a Medicare Advantage plan that includes it.⁷ In 2026, no Part D plan can set a deductible higher than $615, and total out-of-pocket drug spending is capped at $2,100 for the year. Once you hit that cap, you pay nothing for covered drugs for the rest of the calendar year.⁸

Plan Type Abbreviations

Within Medicare Advantage, several plan structures exist. Medigap and stand-alone drug plans round out the main choices.

HMO (Health Maintenance Organization): HMO plans generally require you to see doctors and hospitals in the plan’s network, except for emergencies and urgent care. Most also require a referral to see a specialist.⁹ The tradeoff is typically lower out-of-pocket costs.

PPO (Preferred Provider Organization): PPO plans let you see both in-network and out-of-network providers for covered services, though going out of network costs more.¹⁰ Referrals to specialists usually aren’t required.

PFFS (Private Fee-for-Service): A PFFS plan is a Medicare Advantage plan where the plan itself sets the payment terms for providers rather than using a fixed network. You can see any Medicare-approved provider who accepts the plan’s terms, and no referrals are needed.¹¹ Providers can decide at each visit whether to accept the plan’s payment conditions, so access can be less predictable.

SNP (Special Needs Plan): SNPs are Medicare Advantage plans restricted to specific populations. You can only enroll if you have certain chronic conditions, live in an institution such as a nursing home, or qualify for both Medicare and Medicaid.¹² Benefits and networks are tailored to the enrollment group.

MSA (Medical Savings Account): An MSA plan pairs a high-deductible Medicare Advantage plan with a special savings account funded by Medicare. You use the account money to pay for care before meeting the deductible. MSA plans do not include drug coverage, so you’d need a separate stand-alone drug plan.¹³

PDP (Prescription Drug Plan): A PDP is a stand-alone plan that adds Part D drug coverage to Original Medicare.⁷

PACE (Program of All-Inclusive Care for the Elderly): PACE provides comprehensive medical and social services to frail, elderly individuals still living in the community. Most PACE participants qualify for both Medicare and Medicaid.¹⁴ A single provider team coordinates doctor visits, hospital care, prescriptions, and home health services.

Medigap (Medicare Supplement Insurance): Medigap is the informal name for Medicare Supplement Insurance, sold by private companies. These standardized policies help cover deductibles, copayments, and coinsurance left over by Original Medicare.¹⁵ You must have both Part A and Part B to buy a Medigap policy, and you cannot use Medigap with a Medicare Advantage plan. It only works alongside Original Medicare.¹⁶

Enrollment Period Abbreviations

Medicare uses several enrollment windows, each with its own initials. Missing the right one can mean delayed coverage or permanent premium penalties.

IEP (Initial Enrollment Period): Your first chance to sign up. The IEP lasts seven months: three months before the month you turn 65, your birthday month, and the three months after. Signing up in the first three months gets you coverage fastest.¹⁷
GEP (General Enrollment Period): If you missed your IEP, the GEP runs January 1 through March 31 each year. Coverage starts the month after you sign up. Enrolling through the GEP usually triggers a late enrollment penalty.¹⁷
AEP (Annual Enrollment Period): Also called Open Enrollment, this runs October 15 through December 7. You can switch Medicare Advantage plans, join or drop Part D, or move between Original Medicare and Medicare Advantage. Changes take effect January 1.¹⁸
OEP (Open Enrollment Period for Medicare Advantage): January 1 through March 31. Current Medicare Advantage enrollees can make a single change: switch to a different MA plan, or drop it and return to Original Medicare with a stand-alone drug plan. This window does not apply to people already in Original Medicare.
SEP (Special Enrollment Period): Life changes can open a SEP outside the normal windows. Common triggers include moving to a new service area, losing employer coverage, gaining or losing Medicaid eligibility, and being released from incarceration. The length varies by event.¹⁹

Cost and Income Abbreviations

IRMAA (Income-Related Monthly Adjustment Amount) is the surcharge higher-income beneficiaries pay on top of the standard Part B and Part D premiums. Whether you owe IRMAA depends on your MAGI (Modified Adjusted Gross Income) from the tax return filed two years prior. In 2026, individuals with MAGI at or below $109,000 (or $218,000 filing jointly) pay the standard premiums with no surcharge. Above those thresholds, the Part B surcharge starts at $81.20 per month and rises through five tiers, reaching $487.00 per month at $500,000 or more in individual income. Part D has its own parallel IRMAA brackets, starting at $14.50 per month and topping out at $91.00.² If your income has dropped significantly since the tax year used for the calculation, from retirement, divorce, or the death of a spouse, you can ask Social Security to use more recent income figures.

MOOP (Maximum Out-of-Pocket) is the annual spending cap built into every Medicare Advantage plan. Once your cost-sharing for covered services hits the plan’s MOOP limit, the plan covers everything else for the rest of the year. For 2026, CMS set the maximum allowable MOOP for Medicare Advantage at $9,250, though many plans set their own limits below that ceiling. Part D drug costs don’t count toward the MA plan’s MOOP.

LEP (Late Enrollment Penalty) is the ongoing premium surcharge you pay if you delay signing up for Part B or Part D without qualifying coverage. The Part B penalty adds 10% to your monthly premium for each full 12-month period you could have enrolled but didn’t, and it lasts as long as you have Part B. The Part D penalty adds 1% of the national base beneficiary premium ($38.99 in 2026) for each full month you went without creditable drug coverage, and it sticks for as long as you have Part D.²⁰

Help-with-Costs Abbreviations

LIS (Low Income Subsidy), commonly called Extra Help, is a federal program that helps people with limited income pay Part D premiums, deductibles, and copayments. In 2026, individuals with income up to $23,940 and resources up to $18,090 may qualify; the limits are $32,460 and $36,100 for married couples. Under Extra Help, copayments drop to $5.10 for generics and $12.65 for brand-name drugs, and once total drug costs reach $2,100, you pay nothing for the rest of the year.²¹ People receiving full Medicaid, Supplemental Security Income, or help from a Medicare Savings Program qualify automatically.

MSP (Medicare Savings Programs) are state-administered programs that help pay Medicare premiums and, in some cases, deductibles and coinsurance. Four types exist:

QMB (Qualified Medicare Beneficiary): Covers Part A and Part B premiums, deductibles, coinsurance, and copayments. 2026 monthly income limit: $1,350 for individuals.
SLMB (Specified Low-Income Medicare Beneficiary): Covers Part B premiums. Monthly income limit: $1,616 for individuals.
QI (Qualifying Individual): Also covers Part B premiums, for those slightly above SLMB limits. Monthly income limit: $1,816 for individuals.
QDWI (Qualified Disabled and Working Individual): Covers Part A premiums for people with disabilities who returned to work and lost premium-free Part A. Monthly income limit: $5,405 for individuals.

All four programs have higher income limits in Alaska and Hawaii, and some states set their thresholds above the federal minimums.²²

Administrative and Medical Abbreviations

CMS (Centers for Medicare & Medicaid Services) is the federal agency that administers the entire Medicare program under the Department of Health and Human Services. CMS writes the rules governing benefits, provider payments, and the approval of private Medicare plans.²³

DME (Durable Medical Equipment) refers to reusable, medically necessary items prescribed by a doctor for home use. Common examples include hospital beds, wheelchairs, oxygen equipment, and nebulizers. Part B covers DME.³

SNF (Skilled Nursing Facility) describes a facility that provides continuous, high-level care such as physical therapy or IV medications after a qualifying inpatient hospital stay. Part A covers SNF care for a limited number of days following at least three consecutive days of inpatient hospitalization.¹

ESRD (End-Stage Renal Disease) refers to permanent kidney failure requiring ongoing dialysis or a kidney transplant. ESRD is one of the conditions that qualifies someone under 65 for Medicare.²⁴ The other condition that triggers automatic eligibility is ALS (Amyotrophic Lateral Sclerosis), also called Lou Gehrig’s disease.²⁵

MBI (Medicare Beneficiary Identifier) is the unique, randomly generated ID number printed on current Medicare cards. It replaced the older HICN (Health Insurance Claim Number), which was based on the beneficiary’s Social Security number. CMS completed the switch to protect beneficiaries from identity theft, and all Medicare claims now require the MBI. If you still have an old card showing a Social Security-based number, you can request a replacement through Medicare or Social Security.

1
Medicare.gov. Inpatient or Outpatient Hospital Status Affects Your Costs
2
Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles
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Medicare.gov. What Part B Covers
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Medicare.gov. Parts of Medicare
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HHS.gov. What Is Medicare Part C
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Medicare.gov. Whats Medicare Drug Coverage Part D
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Medicare.gov. Choose How You Get Drug Coverage
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Medicare.gov. How Much Does Medicare Drug Coverage Cost
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Medicare.gov. Health Maintenance Organizations HMOs
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Medicare.gov. Preferred Provider Organizations PPOs
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Medicare.gov. Private Fee-for-Service PFFS Plans
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Centers for Medicare & Medicaid Services. Medicare Special Needs Plans
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Centers for Medicare & Medicaid Services. Your Guide to Medicare Medical Savings Account MSA Plans
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Centers for Medicare & Medicaid Services. Program of All-Inclusive Care for the Elderly PACE
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Medicare.gov. Whats Medicare Supplement Insurance Medigap
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Centers for Medicare & Medicaid Services. Medigap Medicare Supplement Health Insurance
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Medicare.gov. When Does Medicare Coverage Start
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Medicare.gov. Open Enrollment
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Medicare.gov. Special Enrollment Periods
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Medicare.gov. Avoid Late Enrollment Penalties
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Medicare.gov. Help With Drug Costs
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Medicare.gov. Medicare Savings Programs
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Centers for Medicare & Medicaid Services. About CMS
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Medicare.gov. End-Stage Renal Disease ESRD
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Medicare.gov. Get Started With Medicare