Medicare enrollment isn't as simple as signing up once you turn 65. There are multiple enrollment periods, different rules depending on your situation, and permanent penalties for late enrollment that can cost you thousands of dollars over your lifetime.
The good news: if you understand the rules, enrollment is straightforward. The key is knowing which enrollment period applies to you and what deadlines you absolutely cannot miss.
Understanding Medicare Enrollment Periods
Medicare has several distinct enrollment periods, each with different purposes and rules. Understanding which ones apply to your situation is crucial.
Initial Enrollment Period (IEP)
This is your first opportunity to enroll in Medicare, and it's the most important window to understand.
When it occurs:
- Begins 3 months before the month you turn 65
- Includes your birthday month
- Ends 3 months after your birthday month
- Total window: 7 months
Example: If your 65th birthday is June 15, your IEP runs from March 1 through September 30.
What you can do:
- Enroll in Part A (hospital insurance)
- Enroll in Part B (medical insurance)
- Enroll in a Part D prescription drug plan
- Enroll in a Medicare Advantage plan (Part C)
When coverage starts:
- Sign up during the 3 months before your birthday month → Coverage starts the 1st of your birthday month
- Sign up during your birthday month → Coverage starts the 1st of the following month
- Sign up during the 3 months after your birthday month → Coverage is delayed 1-3 months
Don't Wait Until the End
Enrolling early in your IEP ensures your coverage starts on your 65th birthday. Waiting until the end of your IEP delays your coverage by up to 3 months—during which you'll have no Medicare protection.
Special Enrollment Period (SEP)
If you delay Medicare because you have employer coverage, you qualify for a Special Enrollment Period when that coverage ends.
Who qualifies:
- People who delayed Part B because they had coverage through current employment (their own or spouse's)
- Employer must have 20+ employees
- Coverage must be through active employment—COBRA and retiree coverage don't count
When it occurs:
- You can enroll anytime while still covered by employer insurance
- After coverage ends, you have an 8-month window to enroll
- The 8 months start from when employment ends OR when coverage ends, whichever comes first
No penalty: Using the SEP allows you to enroll without late enrollment penalties.
General Enrollment Period (GEP)
If you missed your Initial Enrollment Period and don't qualify for a Special Enrollment Period, the GEP is your only option.
When it occurs: January 1 through March 31 each year
When coverage starts: July 1
Important: Enrolling during GEP typically means paying late enrollment penalties (see penalty section below).
Medicare Open Enrollment (Annual Election Period)
This period is for changing your Medicare coverage, NOT for initial enrollment.
When it occurs: October 15 through December 7 each year
What you can do:
- Switch from Original Medicare to Medicare Advantage
- Switch from Medicare Advantage to Original Medicare
- Change Medicare Advantage plans
- Join, drop, or switch Part D plans
Changes take effect: January 1 of the following year
Medicare Advantage Open Enrollment Period
When it occurs: January 1 through March 31
Who can use it: People already enrolled in Medicare Advantage
What you can do:
- Switch to a different Medicare Advantage plan
- Switch to Original Medicare (and join a Part D plan)
Who Must Enroll and When
Turning 65 Without Employer Coverage
If you're not working and don't have employer coverage through a spouse:
- Enroll during your Initial Enrollment Period
- Ideally enroll 3 months before your birthday for coverage starting on your birthday
- Sign up for Part A, Part B, and Part D (or Medicare Advantage)
- Missing this window results in penalties
Turning 65 With Employer Coverage
If you're still working with employer coverage (or covered through a working spouse):
- Part A: Usually enroll at 65 (it's free and can serve as secondary coverage)
- Part B: Can delay without penalty if employer has 20+ employees
- Part D: Can delay without penalty if employer drug coverage is "creditable"
- When employment/coverage ends, use Special Enrollment Period within 8 months
Check Employer Size
The 20-employee rule is crucial. If your employer has fewer than 20 employees, Medicare becomes your primary coverage at 65, and you should enroll in Part B immediately to avoid penalties and coverage gaps.
Already Receiving Social Security
If you're already receiving Social Security benefits when you turn 65:
- You'll be automatically enrolled in Part A and Part B
- Your Medicare card will be mailed to you about 3 months before your 65th birthday
- You can decline Part B if you have other coverage (respond to the notice you receive)
- You'll still need to actively enroll in Part D or Medicare Advantage
Disability-Based Medicare
If you receive Social Security Disability Insurance (SSDI):
- You're automatically enrolled in Medicare after 24 months of SSDI
- Different rules apply—consult Medicare directly or review disability-specific resources
Late Enrollment Penalties
This is where many people make costly mistakes. Late enrollment penalties are permanent—you'll pay them every month for as long as you have Medicare.
Part B Late Enrollment Penalty
How it's calculated:
- 10% of the Part B premium for each full 12-month period you could have had Part B but didn't
- The penalty is added to your monthly Part B premium
- You pay this increased premium as long as you have Part B
Example:
- You delay Part B for 2 years without qualifying coverage
- 2024 standard Part B premium: $174.70/month
- Your penalty: 20% (10% x 2 years) = $34.94/month
- Your monthly Part B cost: $209.64
- Extra cost over 10 years: $4,193
- Extra cost over 20 years: $8,386+
Part D Late Enrollment Penalty
How it's calculated:
- 1% of the national base beneficiary premium × number of months without creditable coverage
- 2024 national base premium: $34.70
- Penalty is added to your Part D premium
- Permanent, lasting as long as you have Part D
Example:
- You delay Part D for 24 months without creditable coverage
- Penalty: 24% of $34.70 = $8.33/month
- Added to whatever Part D plan premium you choose
- Extra cost over 10 years: $1,000
Part A Penalty (Rare)
Most people don't pay for Part A (if they have 40 quarters of Medicare-taxed work). For those who must pay:
- Penalty: 10% higher premium for twice the number of years you delayed
- Example: Delayed 2 years = pay penalty for 4 years
Penalties Are Forever
Unlike some insurance penalties that expire, Medicare late enrollment penalties last for the rest of your life. A 20% Part B penalty assessed at 67 will still be added to your premium when you're 85. This is why getting enrollment right matters so much.
How to Enroll in Medicare
Enrolling in Part A and Part B
You enroll through Social Security, not Medicare. Options include:
Online (Easiest):
- Go to ssa.gov
- Create a my Social Security account if you don't have one
- Click "Apply for Medicare Only"
- Complete the application
- Typically takes 15-20 minutes
By Phone:
- Call Social Security: 1-800-772-1213
- TTY: 1-800-325-0778
- Best to call early morning or late afternoon for shorter wait times
In Person:
- Visit your local Social Security office
- Appointments recommended—schedule online or by phone
Enrolling in Part D (Prescription Drug Coverage)
Part D enrollment is separate from Part A/B:
Options:
- Medicare.gov: Use the Plan Finder tool to compare plans and enroll online
- Directly with insurance companies: Contact the plan you want directly
- Through a licensed insurance agent: They can help you compare and enroll (free to you)
- State Health Insurance Assistance Program (SHIP): Free counseling in every state
Enrolling in Medicare Advantage (Part C)
Medicare Advantage plans are offered by private insurers:
Options:
- Medicare.gov: Plan Finder shows available plans in your area
- Directly with insurance companies: Humana, UnitedHealthcare, Aetna, etc.
- Through a licensed agent: Can help compare options
- SHIP counselors: Unbiased help comparing plans
Medicare and Employer Coverage
How Medicare works with employer coverage depends on employer size and your situation.
If Employer Has 20+ Employees
- Employer insurance is primary (pays first)
- Medicare is secondary
- You can delay Part B without penalty
- Many people still take free Part A as secondary coverage
- When employment ends, use SEP to enroll in Part B
If Employer Has Fewer Than 20 Employees
- Medicare becomes primary at 65
- Employer coverage is secondary
- You should enroll in Part B at 65 to avoid penalties
- Your employer plan may require you to enroll in Medicare
Retiree Coverage
- Does NOT count as current employer coverage
- Does NOT qualify you for Special Enrollment Period
- Enroll in Medicare during your Initial Enrollment Period
- Retiree coverage typically becomes secondary to Medicare
COBRA
- Does NOT count as employer coverage for Medicare purposes
- Does NOT qualify you for Special Enrollment Period
- If you're on COBRA and turn 65, enroll in Medicare immediately
- COBRA coverage may end when you become Medicare-eligible
Coordinate With Your Employer
Before making Medicare decisions, talk to your employer's HR department about how your coverage works with Medicare. Get any information in writing, especially about whether you can keep employer coverage after enrolling in Medicare and how coordination of benefits works.
Step-by-Step Enrollment Guide
3 Months Before Turning 65
- Review your current coverage: Do you have employer coverage? Will it continue after 65?
- Decide what you need: Original Medicare + Medigap + Part D, or Medicare Advantage?
- Research plans: Use Medicare.gov Plan Finder or consult SHIP counselors
- Enroll in Part A and Part B: Through ssa.gov or Social Security
- Enroll in Part D or Medicare Advantage: Through Medicare.gov or directly with insurers
Documents You'll Need
- Social Security number
- Date of birth
- Citizenship/residency documentation (if not already on file with Social Security)
- Current address
- Information about current health coverage
- For SEP: employer coverage termination letter and employment end date
After You Enroll
- Your Medicare card arrives by mail (usually within a few weeks)
- If you enrolled in a Part D or Advantage plan, you'll receive a separate card from that insurer
- Premiums are deducted from Social Security (if receiving) or billed quarterly
- Keep enrollment confirmation documents for your records
Common Enrollment Mistakes to Avoid
Mistake 1: Assuming Medicare Is Automatic
Only those already receiving Social Security are automatically enrolled. Everyone else must actively sign up. Don't wait for Medicare to contact you.
Mistake 2: Thinking COBRA Counts as Employer Coverage
COBRA does not protect you from late enrollment penalties. If you're on COBRA when turning 65, enroll in Medicare during your IEP.
Mistake 3: Missing the 8-Month SEP Window
After employer coverage ends, you have exactly 8 months to enroll. There's no extension or grace period. Mark your calendar.
Mistake 4: Enrolling Too Late in Your IEP
Waiting until the last months of your IEP delays your coverage start date. Enroll in the first 3 months for coverage starting on your birthday.
Mistake 5: Not Enrolling in Part D
Even if you don't take many medications now, enroll in Part D during your IEP to avoid permanent late penalties. Basic plans can cost under $10/month.
Mistake 6: Confusing Open Enrollment with Initial Enrollment
Annual Open Enrollment (October-December) is for changing plans, not initial enrollment. Don't wait until October if you're newly eligible.
Getting Help with Medicare Enrollment
SHIP (State Health Insurance Assistance Program)
- Free, unbiased Medicare counseling in every state
- Trained volunteers help with enrollment decisions
- No pressure to buy any specific plan
- Find your local SHIP: shiphelp.org or 1-877-839-2675
Medicare.gov
- Official Medicare website
- Plan Finder tool for comparing options
- Enrollment information and forms
- 1-800-MEDICARE (1-800-633-4227) for questions
Social Security
- Handles Part A and Part B enrollment
- ssa.gov for online enrollment
- 1-800-772-1213 for phone assistance
- Local offices for in-person help
Licensed Insurance Agents
- Can help compare and enroll in Part D and Advantage plans
- Services are free to you (they're paid by insurers)
- Be aware they may favor certain plans
- Good for guidance but verify with unbiased sources
Frequently Asked Questions
Sign up during your Initial Enrollment Period, which starts 3 months before your 65th birthday month and ends 3 months after. For coverage starting on your birthday, enroll in the first 3 months of this window. If you have employer coverage, you may delay enrollment.
Late enrollment penalties increase your premiums permanently. Part B penalty: 10% for each year you delayed enrollment. Part D penalty: 1% per month without creditable coverage. These penalties last as long as you have Medicare.
Yes, you can delay Part B without penalty if you have coverage through current employment with an employer of 20+ employees. When coverage ends, you have 8 months to enroll. COBRA and retiree coverage do NOT qualify for this exception.
Sign up online at ssa.gov, by calling Social Security at 1-800-772-1213, or by visiting your local Social Security office. For Part D or Medicare Advantage, enroll through medicare.gov or directly with insurance companies.
If you miss your Initial Enrollment Period and don't qualify for Special Enrollment, you must wait for General Enrollment (January 1-March 31) with coverage starting July 1. You'll also face permanent late enrollment penalties.
Medicare Open Enrollment runs October 15 through December 7 each year. During this time, you can switch Medicare plans. This is for changing plans, not initial enrollment. Changes take effect January 1.
If receiving Social Security, you'll be automatically enrolled in Part A at 65. Since Part A is free for most people, there's usually no reason to decline it—it can serve as secondary coverage alongside your employer plan.
Initial Enrollment Period: 7-month window around your 65th birthday. Special Enrollment Period: 8 months after losing employer coverage. General Enrollment Period: January 1-March 31 for those who missed initial enrollment. Open Enrollment: October 15-December 7 for changing plans.
Don't Let Deadlines Slip
Medicare enrollment rules are unforgiving. Missing a deadline by even one day can result in penalties you'll pay for the rest of your life. The system isn't designed for forgiveness—it's designed to ensure everyone enrolls on time.
The good news is that if you understand the rules, enrollment is straightforward. Know your Initial Enrollment Period dates. If you have employer coverage, understand exactly when your Special Enrollment Period ends. When in doubt, consult SHIP counselors—they provide free, unbiased guidance.
Mark your calendar with enrollment deadlines. Set reminders. Don't assume Medicare will contact you or that enrollment is automatic (unless you're already on Social Security). Take control of your Medicare enrollment, and you'll avoid the costly mistakes that trip up so many others.