Medicare Enrollment Guide: When and How to Sign Up

Financial Disclaimer: This article is for informational and educational purposes only. It does not constitute personalized financial, investment, legal, or tax advice. Consult a qualified financial professional before making any financial decisions. Past performance does not guarantee future results.

Medicare enrollment is one of the most consequential administrative decisions in retirement. Miss the window and you face permanent premium penalties that compound every year for the rest of your life. Enroll too early when you should not, and you may be paying for coverage you do not need. According to CMS, the standard Part B premium for 2026 is $202.90 per month — but IRMAA surcharges can push that above $689.90 for high-income retirees.

This guide covers every enrollment window, the penalties for missing them, and how to coordinate Medicare with employer coverage.

Medicare Parts: What Each Covers

Part	Coverage	2026 Cost	Enrollment
Part A (Hospital)	Inpatient hospital, skilled nursing, hospice	$0 premium for most (40+ work credits)	Automatic at 65 if receiving Social Security
Part B (Medical)	Doctor visits, outpatient care, preventive services	$202.90/month standard	Must actively enroll
Part C (Medicare Advantage)	Bundles A + B + usually D through private insurers	Varies by plan	Separate enrollment during AEP or IEP
Part D (Prescription Drug)	Prescription medications	~$46.50/month average	Must actively enroll

Source: Medicare.gov

The Initial Enrollment Period (IEP)

Your IEP is a 7-month window centered on your 65th birthday:

Begins: 3 months before your birthday month
Includes: Your birthday month
Ends: 3 months after your birthday month

Example: If you turn 65 in June 2026, your IEP runs March through September 2026.

When coverage starts depends on when you sign up:

Sign Up During	Coverage Begins
3 months before birthday month	Birthday month (day 1)
Birthday month	1 month after enrollment
1-3 months after birthday month	2-3 months after enrollment

Sign up during the first three months of your IEP for coverage to begin on time. Waiting until after your birthday month creates a gap.

Late Enrollment Penalties

Miss your IEP without qualifying for a Special Enrollment Period and you face penalties:

Part B late penalty: 10% added to your Part B premium for every full 12-month period you could have had Part B but did not. This penalty is permanent — you pay it for the rest of your life.

Part D late penalty: 1% of the national base beneficiary premium ($36.78 in 2026) multiplied by the number of months you went without creditable prescription drug coverage. Also permanent.

Example: If you delay Part B for 3 years without qualifying for an exception, you pay a 30% penalty on top of the standard premium. At $202.90, that adds $60.87/month — $730/year — for life.

Source: SSA — Medicare Premiums

Special Enrollment Period (SEP): If You Are Still Working at 65

If you are covered by an employer group health plan (through your own or your spouse’s current employment) when you turn 65, you can delay Part B enrollment without penalty.

Key rules:

The employer plan must be from current employment (not COBRA, not retiree health benefits)
The employer must have 20 or more employees
Once you stop working or lose employer coverage, you have an 8-month SEP to enroll in Part B
COBRA coverage does not count as employer coverage for Medicare SEP purposes — this is the most common and costly mistake

If your employer has fewer than 20 employees: Medicare becomes primary at 65 regardless. You should enroll during your IEP.

Source: CMS — Medicare & You Handbook

Higher-income retirees pay more for Medicare Part B and Part D through IRMAA (Income-Related Monthly Adjustment Amount). IRMAA is based on your Modified Adjusted Gross Income (MAGI) from two years prior — so your 2026 premiums are based on your 2024 tax return.

2026 IRMAA brackets (CMS):

Single MAGI (2024)	Joint MAGI (2024)	Part B Premium	Part D Surcharge
$109,000 or less	$218,000 or less	$202.90	$0.00
$109,001-$137,000	$218,001-$274,000	$284.10	$14.50
$137,001-$171,000	$274,001-$342,000	$405.50	$37.50
$171,001-$205,000	$342,001-$410,000	$526.90	$60.40
$205,001-$500,000	$410,001-$750,000	$608.10	$83.50
Over $500,000	Over $750,000	$689.90	$91.00

IRMAA planning strategies:

Time Roth conversions to avoid pushing MAGI above thresholds
Use Qualified Charitable Distributions (QCDs) to reduce AGI at 70 1/2+
If you experienced a life-changing event (retirement, death of spouse, divorce), file SSA-44 to request an IRMAA reduction based on current income
Manage RMD distributions to stay below bracket thresholds

Medicare vs Employer Coverage: Decision Framework

If you are 65 and still working with employer coverage, use this framework:

Enroll in Part A regardless (it is free and coordinates with employer coverage). Part A does not affect your HSA eligibility if you have not yet filed for Social Security.

Delay Part B if:

Your employer has 20+ employees
The employer plan provides comparable or better coverage
You want to continue contributing to an HSA (requires delaying Part A as well if you want to keep contributing)

Enroll in Part B if:

Your employer has fewer than 20 employees (Medicare is primary)
Your employer plan has high premiums or poor coverage
You are retiring within 6-8 months anyway

HSA interaction: You cannot contribute to an HSA once you enroll in any part of Medicare, including Part A. If you are 65 and want to keep funding your HSA, you must delay both Part A and Part B. Be aware that filing for Social Security automatically enrolls you in Part A.

Healthcare Bridge: Before Medicare at 65

If you retire before 65, you need coverage during the gap. Options include:

ACA Marketplace plans — income-based subsidies may apply
COBRA — up to 18 months of former employer coverage (expensive, no subsidy)
Spouse’s employer plan — if your spouse is still working
Healthcare sharing ministries — not insurance, limited coverage

For the full analysis: Healthcare Bridge Strategy Before Medicare at 65

Annual Enrollment Period (AEP): October 15 - December 7

Every year, the AEP lets you:

Switch between Original Medicare and Medicare Advantage
Change Medicare Advantage plans
Add, drop, or change Part D prescription drug plans
Changes take effect January 1

Review your coverage annually. Drug formularies, premiums, and provider networks change every year.

Key Takeaways

Your Initial Enrollment Period is 7 months centered on your 65th birthday — do not miss it
Late enrollment penalties for Part B are 10% per year of delay, permanent for life
COBRA does not count as employer coverage for Medicare purposes — this is the costliest common mistake
IRMAA surcharges are based on income from two years prior and can add $80-$490 to monthly Part B premiums
You cannot contribute to an HSA after enrolling in any part of Medicare
Review coverage annually during the October 15 - December 7 AEP window

Next Steps

Read Retirement Planning in Your 60s for the full transition strategy
Explore retirement tax planning to manage IRMAA thresholds
Return to the retirement planning by decade roadmap

This content is for educational purposes only and does not constitute financial advice. Consult a licensed financial professional for your specific situation.