Plain English
The glossary
Acronyms are still a war crime. Here they are anyway.
AEPAnnual Enrollment Period. October 15 through December 7 each year. Your window to switch Medicare Advantage or Part D plans. Changes take effect January 1.
ALJAdministrative Law Judge. The third level of the Medicare appeals process. Real courtroom, real reversal rates, many denials get overturned here.
ANOCAnnual Notice of Change. The letter your Medicare Advantage or Part D plan must send you by September 30 explaining what changes in the upcoming year. Don’t throw this away.
Benefit PeriodHow Medicare counts a hospital stay. Starts the day you’re admitted as an inpatient. Ends after you’ve been out of the hospital and any skilled nursing facility for 60 consecutive days. The Part A deductible resets with each new benefit period, not each year.
Birthday RuleA state law (available in select states) allowing you to switch to the same or lesser Medigap plan once a year around your birthday without medical underwriting. Check Appendix A for states that have it.
CMSCenters for Medicare and Medicaid Services. The federal agency that actually runs Medicare. Different from Social Security, which handles enrollment. Two agencies, one nightmare.
COBRAContinuation coverage from your former employer. Keeps your old plan going after you leave a job. Critical warning: COBRA does NOT count as creditable coverage for delaying Part B. Your IEP clock runs regardless.
CoinsuranceYour percentage share of a covered service after you’ve met your deductible. Under Original Medicare Part B, you typically pay 20% of the Medicare-approved amount. There’s no cap on that 20% unless you have supplemental coverage.
CopayA fixed dollar amount you pay per service, typically used in Medicare Advantage and Part D plans. $10 for a generic drug. $40 for a specialist visit. Unlike coinsurance, the number doesn’t scale with the bill.
Creditable CoverageDrug or health coverage that’s at least as good as standard Medicare. Having creditable coverage lets you delay Part A, Part B, or Part D enrollment without owing late penalties later. Get this in writing from your employer or insurer.
Custodial CareHelp with daily activities, bathing, dressing, eating, walking. Medicare doesn’t cover this. Not a dollar. This is the coverage gap that catches families completely off guard when a parent or spouse needs long-term support.
DeductibleThe amount you pay out of pocket before Medicare or your plan starts sharing costs. Part A has a per-benefit-period deductible. Part B has an annual deductible. Part D plans may have their own deductible up to the annual maximum.
Dual EligibleA person who qualifies for both Medicare and Medicaid. Dual eligibles often get enhanced coverage, $0 premiums, and automatic Extra Help for drug costs. If you’re in this category, make sure you’re enrolled in everything you qualify for.
Extra HelpA federal program (also called Low Income Subsidy or LIS) that reduces Part D prescription drug costs for lower-income Medicare enrollees. Covers most or all premiums, deductibles, and copays. Millions of people qualify and don’t know it.
FEHBFederal Employees Health Benefits program. If you’re a federal employee or retiree, your FEHB plan coordinates with Medicare in specific ways. Read the “When You Have Medicare” section of your FEHB plan document carefully.
FormularyYour Part D drug plan’s official list of covered medications, organized into tiers by cost. A drug not on the formulary isn’t covered at plan pricing. Formularies change every year. Check yours every October.
GI (Guaranteed Issue)Your legal right to buy a Medigap plan without medical underwriting, meaning the insurer can’t reject you or charge you more based on health conditions. You have GI rights during your 6-month Medigap open enrollment window. Miss it and you may face medical underwriting forever after.
HDGHigh Deductible Plan G. The lowest-premium Medigap plan that still provides comprehensive coverage. You pay all costs until you hit the annual HDG deductible ($2,950 in 2026), then Medigap covers everything. Best for healthy enrollees who want catastrophic protection without high monthly premiums.
IEPInitial Enrollment Period. The 7-month window centered on your 65th birthday: 3 months before, your birthday month, and 3 months after. Your main chance to enroll in Parts A, B, and D without penalties.
IRMAAIncome-Related Monthly Adjustment Amount. Higher Medicare premiums charged to higher-income beneficiaries. Based on your tax return from 2 years prior. Starts at $109,000 for individuals in 2026. Fully appealable if your income has since dropped due to a qualifying life change.
LEPLate Enrollment Penalty. A permanent premium surcharge for missing Medicare enrollment windows without creditable coverage. Part B LEP: 10% per year of delay, forever. Part D LEP: 1% of the national base premium per month of delay, also forever.
LISLow Income Subsidy. Same program as Extra Help. Some documents use one term, some use the other. Same benefit.
MAMedicare Advantage. Also called Part C. A private-plan alternative to Original Medicare, sold by insurers and approved by CMS. Usually includes drug coverage. Often has $0 premium but higher out-of-pocket costs during serious illness. Networks and prior authorizations apply.
MedigapSupplemental insurance that fills the gaps Original Medicare leaves, deductibles, coinsurance, copays. Also called Medicare Supplement. Plans are standardized by letter (A, B, D, G, K, L, M, N). Plan G and High Deductible Plan G are the most popular for new enrollees.
MSNMedicare Summary Notice. A quarterly statement mailed to you showing what was billed to Medicare on your behalf. Review every line. Billing errors and outright fraud show up here. Report anything you don’t recognize to 1-800-MEDICARE.
MSPMedicare Savings Program. State-run programs that help pay for Part B premiums, deductibles, and cost-sharing for qualifying lower-income Medicare enrollees. Four tiers: QMB, SLMB, QI, QDWI. Apply through your state Medicaid office.
Observation StatusAn outpatient designation hospitals use for patients who haven’t been formally admitted. Observation days don’t count toward the 3-day inpatient stay required for Medicare to cover skilled nursing. You can spend 5 days in a hospital room under observation and still owe full skilled nursing costs. Always ask.
OEPOpen Enrollment Period. For Medicare Advantage specifically: January 1 through March 31 each year. Lets you switch MA plans or return to Original Medicare. Doesn’t apply to Medigap.
Original MedicareParts A and B together, run directly by the federal government. Freedom to see any Medicare-accepting doctor nationwide. No prior authorizations. No network restrictions. No out-of-pocket maximum on its own, which is why most people pair it with a Medigap plan.
PACEProgram of All-Inclusive Care for the Elderly. Available in 33 states for people 55+ who are nursing-home eligible but want to stay in the community. One care team handles everything: medical care, meals, transportation, personal care. Can be fully covered for dual-eligible individuals.
Prior AuthorizationAn insurer’s advance approval requirement before certain services or drugs are covered. Common in Medicare Advantage, not in Original Medicare. If your MA plan denies a prior auth, appeal immediately, especially for urgent care.
PSHBPostal Service Health Benefits. The replacement for FEHB coverage for postal workers, effective 2025. Postal retirees must enroll in Part B to keep PSHB benefits.
SEPSpecial Enrollment Period. A time-limited window triggered by qualifying life events, leaving employer coverage, moving out of a plan’s service area, becoming dual-eligible, etc. SEPs let you change coverage outside normal enrollment windows. Each SEP has its own rules and deadlines.
SHIPState Health Insurance Assistance Program. Free, unbiased Medicare counseling provided by trained volunteers in every state. They have no financial stake in what you choose. Find your local SHIP counselor at shiphelp.org. Use them.
SNFSkilled Nursing Facility. Medicare covers up to 100 days of SNF care after a qualifying 3-day inpatient hospital stay. Days 1-20 are fully covered. Days 21-100 require daily coinsurance ($217.00 in 2026). Day 101 and beyond: you pay everything.
SNPSpecial Needs Plan. A type of Medicare Advantage designed for specific populations: people with certain chronic conditions, dual-eligible individuals, or people in institutions. Usually has enhanced benefits relevant to the specific condition.
SPAPState Pharmaceutical Assistance Program. Some states run their own programs to help with drug costs beyond federal Extra Help. Availability, eligibility, and benefits vary by state. Ask your SHIP counselor whether your state has one.
SSASocial Security Administration. The agency that handles Medicare enrollment, separate from CMS, which runs the program. You enroll at ssa.gov or at a local SSA office. SSA and CMS don’t automatically share information, which is exactly as helpful as it sounds.
Accountable Care Organization (ACO)Group of doctors and hospitals that coordinate care for Medicare patients to improve quality and reduce cost. You may not even know you are in one. (See Ch 9.)
Advance Beneficiary Notice (ABN)Form your provider gives you when Medicare may not cover a service. You sign it agreeing to pay if Medicare denies. Always read it before signing. (See Ch 18.)
Advance Care PlanningDoctor-led conversation about your treatment preferences if you can no longer speak for yourself. Covered by Medicare at no cost during your Annual Wellness Visit. (See Ch 32.)
Annual Enrollment Period (AEP)October 15 to December 7 each year. Window to switch Medicare Advantage plans or Part D plans for the following year. (See Ch 11.)
Annual Notice of Change (ANOC)Letter your Medicare Advantage or Part D plan sends each fall describing what will change next year (premium, copays, formulary, network). Read it. (See Ch 9.)
Annual Wellness VisitYearly preventive visit with your primary care doctor. Includes depression screening, cognitive assessment, fall risk, advance care planning. No cost to you. (See Ch 3.)
AppealFormal challenge to a Medicare or plan coverage denial. Five levels available. You usually have 60 to 120 days to file depending on the type. (See Ch 18.)
AssignmentProvider agreement to accept the Medicare-approved amount as full payment. If your provider does not accept assignment, you can be charged up to 15 percent more (the ’limiting charge’). (See Ch 3.)
Authorized RepresentativePerson you designate (via Form CMS-1696) to speak with Medicare, your MA plan, or your Part D plan on your behalf. Required for most phone calls if you are not the beneficiary. (See Ch 31.)
Benefit Period (Part A)Begins the day you enter a hospital and ends 60 days after discharge. You can have multiple benefit periods in a year, each with its own deductible. (See Ch 2.)
Birthday Rule (Medigap)State-specific annual window to switch Medigap plans without medical underwriting. See Appendix A for the 10 states that have one. (See Ch 14.)
CoinsurancePercentage of cost you pay after meeting the deductible. Typically 20 percent for Part B. (See Ch 3.)
Coordination of BenefitsRules determining which insurance pays first when you have more than one (Medicare plus employer plan, plus TRICARE, plus VA, etc.). (See Ch 13.)
Copay (Copayment)Fixed dollar amount per visit, service, or prescription. Used by Medicare Advantage and Part D plans more than Original Medicare. (See Ch 9.)
Coverage Gap (Donut Hole)Old phase of Part D between initial coverage and catastrophic coverage. ELIMINATED as of 2025 by the Inflation Reduction Act ($2,000 annual cap in 2025, $2,100 in 2026). (See Ch 10.)
Creditable CoverageInsurance considered as good as Medicare, which allows you to delay Part B or Part D without a late enrollment penalty. Marketplace plans and COBRA do NOT count. (See Ch 11.)
DeductibleAnnual amount you pay out of pocket before insurance starts paying. Part A and Part B each have their own. (See Ch 3.)
Dual EligibleQualified for both Medicare AND Medicaid. Triggers extra protections including QMB program. (See Ch 20.)
End-Stage Renal Disease (ESRD)Permanent kidney failure requiring dialysis or transplant. Qualifies you for Medicare at any age (not just 65 plus). (See Ch 30.)
Explanation of Benefits (EOB)Notice from your Medicare Advantage or Part D plan showing what was billed, what the plan paid, and what you owe. Different from a bill. (See Ch 18.)
Extra Help (Low-Income Subsidy or LIS)Federal program that helps pay Part D premiums, deductibles, and copays for lower-income beneficiaries. Apply at ssa.gov/extrahelp. (See Ch 20.)
FormularyList of prescription drugs your Part D or Medicare Advantage plan covers, organized into tiers. Plans can change formulary year to year. (See Ch 10.)
Formulary ExceptionRequest your plan cover a non-formulary drug, or waive a quantity limit or prior authorization. Your doctor must support the request. (See Ch 10.)
General Enrollment Period (GEP)January 1 to March 31 each year. Window for people who missed their Initial Enrollment Period to enroll in Part B. Coverage starts the following month. Late enrollment penalty applies. (See Ch 11.)
Guaranteed Issue RightPeriod when Medigap insurers must sell you a policy without medical underwriting. Triggered by specific qualifying events. (See Ch 7.)
High Deductible Plan G (HDG)Medigap plan with low monthly premium ($40 to $80 typical) but $2,950 annual deductible in 2026. Good for healthy buyers who can absorb the deductible. (See Ch 8.)
Initial Enrollment Period (IEP)7-month window centered on your 65th birthday month. Your first chance to enroll in Medicare. Miss it and you risk lifetime late enrollment penalties. (See Ch 11.)
Late Enrollment PenaltyPermanent premium surcharge for missing your Part B or Part D enrollment window without creditable coverage. Part B: 10 percent per 12 months delayed. Part D: 1 percent of national base per month. (See Ch 11.)
Lifetime Reserve Days60 extra hospital days you can use ONCE in your lifetime after you exhaust day 90 of a benefit period. $868/day in 2026. (See Ch 2.)
MAGI (Modified Adjusted Gross Income)Income calculation used to determine IRMAA bracket. Adds tax-exempt interest back to AGI. (See Ch 12.)
MedicaidJoint federal-state program for low-income individuals. Coordinates with Medicare for dual eligibles. Each state runs its own. (See Ch 20.)
Medicare Advantage (Part C, MA, or MAPD)Private plan that replaces Original Medicare. Usually includes Part D. Often $0 premium but with network restrictions and prior authorizations. (See Ch 9.)
Medicare Savings Program (MSP)State-administered program that helps pay Medicare costs for limited-income beneficiaries. Four levels: QMB, SLMB, QI, QDWI. (See Ch 20.)
Medigap (Medicare Supplement)Private insurance that fills the gaps in Original Medicare. Standardized plans labeled A through N. Plan G is the most common new purchase. (See Ch 7.)
NetworkGroup of providers and facilities your Medicare Advantage or Part D plan contracts with. Going out of network usually costs more or is not covered. (See Ch 9.)
Open Enrollment Period (Medigap)6-month window starting the first month you are 65 AND enrolled in Part B. The ONLY guaranteed window to buy Medigap without medical underwriting in most states. (See Ch 7.)
Original MedicareThe traditional fee-for-service Medicare administered by the federal government. Includes Part A (hospital) and Part B (medical). (See Ch 1.)
Out-of-Pocket Maximum (MOOP)Annual cap on what you pay for covered services. Medicare Advantage plans have one. Original Medicare WITHOUT a Medigap policy does NOT have one. (See Ch 4.)
Part AHospital insurance. Free for most beneficiaries based on payroll history. Covers inpatient hospital, skilled nursing facility, hospice, home health. (See Ch 2.)
Part BMedical insurance. Standard premium $202.90/month in 2026. Covers doctor visits, outpatient services, preventive care, durable medical equipment. (See Ch 3.)
Part DPrescription drug coverage. Sold by private insurers approved by Medicare. New $2,100 annual out-of-pocket cap in 2026. (See Ch 10.)
POLST/MOLSTPhysician (or Medical) Orders for Life-Sustaining Treatment. State-specific medical order form that translates your advance directives into orders EMTs and hospitals must follow. (See Ch 32.)
Prior AuthorizationPlan approval required before certain services or prescriptions. Common in Medicare Advantage. Can delay or block care. You have appeal rights. (See Ch 18.)
ReconsiderationSecond-level Medicare appeal after an initial denial. Handled by a Qualified Independent Contractor (QIC). (See Ch 18.)
Skilled Nursing Facility (SNF)Medicare-covered short-term rehab facility, typically after a qualifying 3-day inpatient hospital stay. Up to 100 days per benefit period. (See Ch 2.)
Social Security Administration (SSA)Federal agency that handles Medicare enrollment, IRMAA determinations and appeals, and Social Security cash benefits. ssa.gov or 1-800-772-1213. (See Ch 24.)
Special Enrollment Period (SEP)Time outside the standard enrollment windows when you can enroll in or change Medicare coverage due to a qualifying event (job loss, move, marriage, etc.). (See Ch 11.)
Special Needs Plan (SNP)Type of Medicare Advantage plan for people with specific situations: Chronic-SNP (specific conditions), Dual-SNP (dual eligible), Institutional-SNP (long-term care residents). (See Ch 9.)
TRICARE for Life (TFL)Health coverage for military retirees age 65 and older that wraps around Medicare as secondary payer. (See Ch 13.)
Tier (Drug Tier)Cost-sharing level for a specific drug in a Part D or MA-PD formulary. Lower tiers (generics) cost less, higher tiers (specialty) cost more. (See Ch 10.)
No glossary term matches that word.