SOCIAL INSURANCE · 6 MIN READ
Medicare Eligibility, Enrollment Periods, and Penalties
Medicare is the federal health program for people 65 and older and for certain younger people with disabilities. Premium-free Part A goes to those 65+ with 40 quarters of Medicare-covered employment (their own or a spouse's); people short of 40 quarters can buy Premium Part A. Under 65, three doors open Medicare: 24 months of SSDI entitlement, End-Stage Renal Disease (ESRD), or ALS — which waives the wait entirely. For ESRD on regular dialysis, entitlement typically begins the first day of the fourth month of dialysis, and when an ESRD patient also has employer group coverage, that plan pays primary for a 30-month coordination period before Medicare takes over. Enrollment timing is heavily tested. The Initial Enrollment Period (IEP) surrounds the 65th birthday. Miss it without a special enrollment right and you wait for the General Enrollment Period (GEP), January 1 through March 31, with coverage now starting the first of the month after enrollment. The Annual Election Period (AEP), October 15 through December 7, is when beneficiaries switch between Original Medicare and Medicare Advantage or change Part D plans for January 1. A separate MA Open Enrollment Period (January 1-March 31) lets MA enrollees make one switch or return to Original Medicare. Late enrollment is punished differently by part: the Part B penalty is 10% of the standard premium for each full 12-month period of delay, and it lasts for life; the Part A penalty (Premium Part A only) is a flat 10% surcharge paid for just twice the number of years of delay. Two coordination rules complete the picture. Under the Medicare Secondary Payer working-aged rules, an employer group health plan pays primary for a working beneficiary only if the employer has 20 or more employees; with fewer than 20, Medicare is primary, so small-employer workers should take Part B at 65 to avoid claim gaps. Finally, higher-income beneficiaries pay IRMAA surcharges on Part B and Part D premiums, based on Modified Adjusted Gross Income from the tax return filed two years prior; a life-changing event such as retirement or a spouse's death supports a request for a new determination.
Key rules
Premium-free Part A requires age 65 plus 40 quarters of covered work (self or spouse).
Those short of 40 quarters may buy Premium Part A. Under-65 entitlement comes via 24 months of SSDI, ESRD, or ALS (immediate).
Why the exam cares: Eligibility questions hinge on the 40-quarter test and on which disability routes skip or shorten the wait.
The AEP runs October 15 to December 7 with changes effective January 1.
The AEP covers Original Medicare vs. Medicare Advantage switches and Part D changes. The MA-OEP (Jan 1-Mar 31) and the Part B GEP (Jan 1-Mar 31) are different windows with different powers.
Why the exam cares: Date-matching questions are near-guaranteed; distractors swap the AEP, MA-OEP, and GEP windows.
The Part B late penalty is 10% per full 12-month delay — and lasts for life.
Each complete 12-month period the person could have enrolled but did not adds 10% to the premium permanently. GEP coverage now begins the month after enrollment.
Why the exam cares: The lifetime duration is the tested contrast with the time-limited Part A penalty.
The Part A late penalty is a flat 10% paid for twice the years of delay — not lifetime.
It applies only to Premium Part A enrollees (those without 40 quarters). Delay 2 years, pay the 10% surcharge for 4 years.
Why the exam cares: Exams pair Part A and Part B penalties in one question to test the flat/limited vs. per-year/lifetime distinction.
Working-aged MSP: employer plans pay primary only with 20 or more employees.
Below 20 employees, Medicare is primary and the group plan pays second, so the employee should enroll in Part B at 65. IRMAA separately raises Part B/D premiums using MAGI from two years back.
Why the exam cares: Primary-vs-secondary payer scenarios with an employee count are a staple; 20 is the dividing line.
Numbers to memorize
- 40 quarters — Medicare-covered work for premium-free Part A at 65
- 24 months — SSDI entitlement before Medicare (ALS immediate; ESRD starts the fourth month of dialysis)
- 30 months — ESRD coordination period when employer group coverage pays primary
- Oct 15 - Dec 7 — Annual Election Period; Jan 1 - Mar 31 — General Enrollment Period and MA Open Enrollment
- 10% per 12-month delay, lifetime — Part B late penalty; 10% flat for twice the delay years — Part A late penalty
- 20+ employees — group health plan pays primary under the working-aged rule (under 20, Medicare is primary)
Common traps
- Confusing the AEP (Oct 15-Dec 7) with the MA Open Enrollment or General Enrollment Periods (both Jan 1-Mar 31) — remember only the AEP allows full plan switching effective January 1.
- Treating the Part A late penalty like Part B's — remember Part A is a flat 10% for twice the delay years, while Part B compounds 10% per year and never ends.
- Assuming employer coverage is always primary for a working 65-year-old — remember the group plan is primary only when the employer has 20 or more employees.
- Using current-year income for IRMAA — remember the surcharge is based on MAGI from the return filed two years earlier, with relief available for life-changing events.
Make a one-page calendar of the enrollment windows and rehearse the two late-penalty formulas aloud — timing and penalty questions are the most predictable points in this section.
Test it before the exam does
Our L&H bank drills Social Insurance with AI-explained answers. 20 questions free, no signup.
Taking the L&H exam in your state?
Studying for the Life & Health insurance exam? Track every lesson free — progress syncs with the app.
Start free