Reference

Medicare glossary

Plain-language definitions for the Medicare and ACA terms used across the calculators. Each entry explains the idea without assuming you already know the jargon.

Last updated October 28, 2026

Written and maintained by Abdul SamadPunjab, Pakistan

60 terms. Choose a letter or scan the list.

2

20-employee rule: The Medicare coordination rule that turns on employer size for active coverage. At 20 or more employees, the employer plan generally pays first for a worker age 65 or older.

A

Active coverage: Coverage from a current employer while you or your spouse still work there. It can affect when Medicare enrollment is required.
Affordability percentage: The share of household income the IRS treats as an affordable employee-only premium for the year.
Annual enrollment period: A yearly window when people with Medicare can change certain Medicare coverage choices for the next plan year.
Appeal: A formal request to review a coverage, payment, or eligibility decision. The deadline and process depend on the decision.
Asset test: A limit on countable resources used by some benefit programs. The resource rules and exclusions vary by program and state.

C

COBRA: A temporary continuation of group health coverage after a qualifying event. It generally does not count as active employer coverage for Medicare enrollment.
Coinsurance: Your share of a covered service after the deductible, usually a percentage.
Copay: A fixed dollar amount you pay for a covered service or prescription.
Cost-sharing reduction: A Marketplace benefit that lowers deductibles, copays, and coinsurance for eligible people who enroll in a Silver plan.
Countable assets: The resources a program counts when testing eligibility, such as bank accounts and some investments. The rules vary by program and state.
Creditable coverage: Coverage that is at least as good as Medicare for the benefit being delayed. It can protect you from a late-enrollment penalty.

D

Deductible: The amount you pay for covered care before the plan starts paying its share.
Dual eligible: A person who qualifies for both Medicare and Medicaid. The two programs can work together to cover premiums and care costs.

E

Employer group health plan: Health coverage offered through an employer to a group of workers. The plan rules can depend on employer size and whether coverage is active.
Extra Help: The Part D Low-Income Subsidy. It can lower Part D premiums, deductibles, and copays.

F

Family glitch: The gap that can leave family members without affordable employer coverage when only the employee-only premium is tested.
Form SSA-44: The Social Security form used to ask for an IRMAA review after a qualifying life-changing event.
Formulary: The list of prescription drugs a drug plan covers, including the tiers and any rules that apply to each drug.
FPL: Federal Poverty Level. A yearly income guideline published by the federal government and used by many benefit programs.

G

General enrollment period: A yearly Medicare window for people who missed their first chance to enroll and do not qualify for a special enrollment period.

H

Household income: For Marketplace purposes, the combined income of the people on your tax return, not just your own W-2 wages.
HSA: Health Savings Account. A tax-advantaged account paired with a high-deductible health plan. Contributions must stop before Medicare Part A begins.

I

IEP: Initial Enrollment Period. The seven-month window around your 65th birthday when most people first sign up for Medicare.
Income disregard: Income that an eligibility program leaves out when it applies its income test. Disregards can change whether someone qualifies.
IRMAA: Income-Related Monthly Adjustment Amount. An extra Part B and Part D charge when your income is above a set threshold.

L

Late enrollment penalty: A permanent addition to a premium when someone delays enrollment without qualifying coverage. The amount depends on the Medicare part involved.
Life-changing event: An event SSA recognizes when reviewing an IRMAA appeal, such as retirement, marriage, divorce, or the death of a spouse.

M

MAGI: Modified adjusted gross income. It is the income figure used for IRMAA and Marketplace subsidy tests, with some adjustments added back to adjusted gross income.
Medicaid: A joint federal and state program that provides health coverage to eligible people with limited income and resources.
Medicare: The federal health insurance program for people age 65 and older and some younger people with qualifying disabilities or conditions.
Medicare Advantage: A private plan that delivers Medicare Part A and Part B benefits, and sometimes Part D, in place of Original Medicare. Network and authorization rules vary by plan.
Medigap: A private supplemental policy that helps pay some Original Medicare cost sharing. It is not the same as Medicare Advantage.
Minimum value: A standard for employer coverage that pays at least 60% of covered health costs on average.
MSP: Medicare Savings Program. A state program that can help pay Medicare premiums and, for some programs, cost sharing.

N

Network: The doctors, hospitals, pharmacies, and other providers that a health plan has contracted with to provide covered care.

O

Open enrollment period: A yearly window when people can enroll in or change Marketplace coverage, subject to state and federal rules.
Out-of-pocket maximum: The most you pay in covered cost sharing during a plan year before the plan pays the full covered share. Premiums usually do not count toward this limit.

P

Part A: The Medicare hospital insurance part. It covers inpatient care, skilled nursing facility care, hospice, and some home health care.
Part B: The Medicare medical insurance part. It covers doctor visits, outpatient care, preventive services, and some supplies.
Part D: The Medicare prescription drug benefit, sold through private plans.
Premium: The monthly amount you pay to keep a health or drug plan active.
Premium tax credit: A Marketplace subsidy that lowers the monthly cost of a health plan for eligible households.
Premium-free Part A: Part A with no monthly premium because you or a spouse have enough work credits or another qualifying status.
Prior authorization: A plan review that must happen before certain services or drugs are covered. A plan may approve, deny, or limit the request.

Q

QI: Qualifying Individual. A Medicare Savings Program that can pay the Part B premium, with limited funding in some states.
QMB: Qualified Medicare Beneficiary. A Medicare Savings Program that can pay Part A and Part B premiums and cost sharing.

R

Redetermination: The first level of review for a Medicare claim or coverage decision. It is handled by the plan or contractor that made the original decision.
Reduced Part A premium: A lower Part A premium for some people who have some work credits but not enough for premium-free Part A.
Retiree coverage: Health coverage from a former employer after you leave work. It is different from active employer coverage for Medicare enrollment rules.
Roth conversion: Moving money from a traditional IRA or retirement account into a Roth account. The converted amount can raise MAGI and affect IRMAA two years later.

S

SEP: Special Enrollment Period. A time outside the usual enrollment window when you can sign up because of a qualifying event.
SHIP: State Health Insurance Assistance Program. A free counseling service that helps people understand Medicare choices and problems.
SLMB: Specified Low-Income Medicare Beneficiary. A Medicare Savings Program that can pay the Part B premium.
Spend-down: A state Medicaid process that lets someone with income or assets above a limit qualify after spending excess amounts on medical care.
State Medicaid agency: The state office that runs Medicaid and usually processes Medicare Savings Program applications for that state.
Subsidy: Financial help that lowers the cost of coverage or care. The rules and eligibility tests depend on the program.
Surcharge: An extra amount added to a standard premium. IRMAA is an income-related Part B and Part D surcharge.

W

W-2 wages: Wages reported by an employer on a W-2 form. They can differ from the household income used for Marketplace subsidies.
Work credits: Social Security credits earned from taxed work. Enough credits, or a qualifying relationship to a worker, can make Part A premium-free.

How to use this glossary

The calculators show a short definition beside the inputs that need one. Use this page when you want the full entry, or when a letter from Social Security, Medicare, or a state agency uses a term you do not recognize.

A definition explains a rule in general terms. It does not replace the official source, your plan documents, or a decision about your own situation.

Open the calculator hub to see the tools that use these terms.

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