Medicare Enrollment: Everything You Need to Know

Miss a Medicare enrollment deadline and you will pay a penalty surcharge on your premium every month for the rest of your life. Not a fine. Not a one-time fee. A permanent increase that compounds over decades. This guide covers every deadline you need to know.

Medicare is not complicated because the coverage is bad — it is complicated because the enrollment rules are unforgiving. The coverage itself is comprehensive. The deadlines are where people get hurt. We will walk through the four parts, the enrollment windows, the costs, and exactly what happens if you miss a deadline.

What is Medicare?

Medicare is the federal health insurance program for Americans 65 and older (and certain younger people with disabilities). It covers over 65 million people and is the primary health insurance for most retirees. You have likely been paying into it your entire working life through payroll taxes.

You are generally eligible for Medicare if you are:

• 65 or older and a U.S. citizen or permanent legal resident for at least 5 continuous years
• Under 65 with certain disabilities (after 24 months of receiving Social Security disability benefits)
• Any age with End-Stage Renal Disease (ESRD) or Amyotrophic Lateral Sclerosis (ALS)

The Four Parts of Medicare

Medicare is divided into four parts, each covering different services. Understanding these parts is crucial for making informed coverage decisions.

Part A: Hospital Insurance

Medicare Part A covers inpatient hospital care, skilled nursing facility care, hospice care, and some home health care.

What Part A Covers:

• Inpatient hospital stays (semi-private room, meals, nursing care)
• Skilled nursing facility care (up to 100 days after a qualifying hospital stay)
• Hospice care for terminal illness
• Some home health care services

Part A Costs (2025):

• Premium: $0 for most people (if you or your spouse paid Medicare taxes for 40+ quarters)
• Hospital deductible: $1,676 per benefit period
• Hospital coinsurance: $0 for days 1-60, $419/day for days 61-90

Part B: Medical Insurance

Medicare Part B covers medically necessary services like doctor visits, outpatient care, preventive services, and durable medical equipment.

What Part B Covers:

• Doctor and outpatient services
• Preventive services (screenings, vaccines, annual wellness visits)
• Durable medical equipment (wheelchairs, walkers, hospital beds)
• Mental health services
• Ambulance services

Part B Costs (2025):

• Standard premium: $185/month in 2025 (higher for high earners — see IRMAA section below)
• Annual deductible: $257
• Coinsurance: Generally 20% of Medicare-approved amount

Part C: Medicare Advantage

Medicare Advantage plans are offered by private insurance companies approved by Medicare. These plans provide all your Part A and Part B coverage, and often include additional benefits.

Medicare Advantage Features:

• Combines Part A, Part B, and usually Part D in one plan
• Often includes extra benefits (dental, vision, hearing, fitness)
• May have lower out-of-pocket costs but limited provider networks
• You still pay your Part B premium plus any plan premium

Types of Medicare Advantage Plans:

• HMO: Requires using network providers and referrals
• PPO: More flexibility to see out-of-network providers
• PFFS: Pay-for-service with any provider accepting plan terms
• SNP: Special Needs Plans for specific conditions or circumstances

Part D: Prescription Drug Coverage

Medicare Part D provides prescription drug coverage through private insurance plans. You can get Part D as a standalone plan or as part of a Medicare Advantage plan.

How Part D Works:

• Each plan has a formulary (list of covered drugs)
• Drugs are organized into tiers with different cost-sharing
• Coverage includes deductible, initial coverage, and catastrophic phases
• The coverage gap (donut hole) has been largely eliminated

Part D Costs (2025):

• Premium: Varies by plan (national average ~$55/month)
• Deductible: Up to $590 (varies by plan)
• Out-of-pocket maximum: $2,000 (new for 2025)

Medicare Enrollment Periods

Medicare has specific enrollment periods. Missing these windows can result in coverage gaps and permanent premium penalties.

Initial Enrollment Period (IEP)

Your Initial Enrollment Period is a 7-month window around your 65th birthday:

• Begins 3 months before your 65th birthday month
• Includes your birthday month
• Ends 3 months after your birthday month

Special Enrollment Periods (SEP)

You may qualify for a Special Enrollment Period if you have certain life events:

• Employer coverage ending: 8-month SEP when you or your spouse stops working or loses employer coverage
• Moving: SEP when you move to a new area with different plan options
• Losing other coverage: Various SEPs for losing Medicaid, COBRA ending, etc.
• Qualifying life events: Marriage, divorce, or other qualifying changes

Annual Enrollment Period (AEP)

The Annual Enrollment Period runs October 15 - December 7 each year. During this period, you can:

• Switch from Original Medicare to Medicare Advantage (or vice versa)
• Change Medicare Advantage plans
• Join, switch, or drop Part D prescription drug plans

Changes made during AEP take effect January 1 of the following year.

Costs and Premiums

Medicare costs include premiums, deductibles, coinsurance, and copays. Here is a summary for 2025:

Late Enrollment Penalties

This is the part of Medicare that has real financial teeth. If you do not enroll when first eligible and do not have qualifying coverage, the penalties are not a slap on the wrist — they are permanent premium surcharges that last as long as you have Medicare. For most people, that means the rest of your life.

Your Next Steps

1. Create a my Social Security account at ssa.gov - if you are receiving Social Security, you will be automatically enrolled in Part A at 65
2. Determine your enrollment period and mark key dates on your calendar
3. Evaluate your current coverage - if you have employer coverage, check if it is creditable for Medicare purposes
4. Compare your options - Original Medicare vs. Medicare Advantage, and choose a Part D plan
5. Consider Medigap - if choosing Original Medicare, a Medigap policy can help cover out-of-pocket costs