Medicare Enrollment Guide: Periods, Deadlines, and Costs

Missing a Medicare enrollment deadline can trigger late-enrollment penalties that follow you for the rest of your life. Whether you are turning 65, retiring from employer coverage, or simply reviewing your options for the year ahead, understanding Medicare enrollment timelines is critical to avoiding gaps in coverage and unnecessary costs. This guide covers every enrollment period, key dates, current-year cost figures, and the steps to get enrolled correctly. Medicare rules and dollar amounts are updated every year, so treat the figures here as recent reference points and confirm the current numbers at Medicare.gov before you rely on them.

Initial Enrollment Period (IEP)

Your Initial Enrollment Period is a seven-month window centered on your 65th birthday month. It begins three months before the month you turn 65, includes your birthday month, and extends three months after. For example, if you turn 65 in June, your IEP runs from March 1 through September 30 of that year.

During your IEP, you can sign up for Medicare Part A (hospital insurance) and Part B (medical insurance). Most people qualify for premium-free Part A if they or a spouse paid Medicare taxes for at least 10 years. Part B carries a standard monthly premium — about $202.90 for 2026 — with an annual deductible of around $283 for 2026. Higher earners pay more through an income-related monthly adjustment amount (IRMAA), described below. Because these amounts change annually, verify the current premium and deductible at Medicare.gov.

Signing up during the first three months of your IEP ensures coverage starts the first day of the month you turn 65 (or the prior month if your birthday is on the first). Waiting until your birthday month or the three months after can delay the start of coverage. Enrolling as early as possible within your IEP is the safest approach.

General Enrollment Period (GEP)

If you missed your IEP and do not qualify for a Special Enrollment Period, you can sign up during the General Enrollment Period, which runs January 1 through March 31 each year. Under current rules, Part B (and premium Part A, if applicable) coverage begins the first day of the month after you enroll. You may face a Part B late-enrollment penalty of 10% for each full 12-month period you were eligible but not enrolled, and that surcharge is added to your Part B premium for as long as you have Part B.

The GEP is a safety net, not an ideal enrollment path. If you have creditable employer coverage, you may qualify for a Special Enrollment Period instead, which avoids the penalty entirely.

Special Enrollment Periods (SEPs)

Special Enrollment Periods give you additional opportunities to enroll outside the standard windows. The most common SEP is triggered by losing employer or union group health coverage. If you or your spouse were covered by an active-employment group plan while you were eligible for Medicare, you generally get an eight-month SEP to enroll in Part B, starting the month after the employment or the coverage ends, whichever comes first.

Other qualifying events that can trigger SEPs include moving out of your plan’s service area, losing Medicaid eligibility, qualifying for Medicare Extra Help (the Part D Low-Income Subsidy), being released from incarceration, and certain plan or agency errors. There are also newer SEPs for exceptional circumstances. For more on financial assistance, see our guide to Medicare Extra Help, and confirm which SEP applies to your situation at Medicare.gov or with a SHIP counselor.

Annual Election Period (AEP) for Medicare Advantage and Part D

The Medicare Advantage and Part D Annual Election Period — commonly called the Annual Enrollment Period, or AEP — runs from October 15 through December 7 each year. During the AEP you can join, switch, or drop a Medicare Advantage plan; join or switch a standalone Part D prescription drug plan; or move from Medicare Advantage back to Original Medicare with a standalone Part D plan. Changes made during the AEP take effect January 1 of the following year.

This is the primary shopping window for Medicare Advantage and Part D. Every year, plans can change their premiums, formularies, provider networks, and benefit structures, so reviewing your current plan’s Annual Notice of Change (ANOC) and comparing it against alternatives is essential. For a deeper dive, see our Medicare AEP guide.

Medicare Advantage Open Enrollment Period (MA OEP)

The Medicare Advantage Open Enrollment Period runs from January 1 through March 31 each year. During this window, beneficiaries who are already enrolled in a Medicare Advantage plan can switch to a different Advantage plan or disenroll and return to Original Medicare (and add a standalone Part D plan). You can make one change during this period. This window does not apply to people who are already on Original Medicare.

Medigap Open Enrollment Period

Your Medigap (Medicare Supplement) Open Enrollment Period is separate from the other windows. It starts on the first day of the month you are both 65 or older and enrolled in Part B, and it lasts six months. During this period you have guaranteed-issue rights, meaning Medigap insurers must sell you any plan they offer at the standard rate regardless of your health, and they cannot impose waiting periods for pre-existing conditions.

After this six-month window closes, Medigap enrollment is still possible, but in most states insurers can require medical underwriting and may charge more or decline you. Some states offer additional protections — for example, certain states provide an annual birthday-month window to change Medigap plans. This makes your initial enrollment timing especially important. For plan comparisons, see our Compare Medicare Supplement Plans guide.

Part D Enrollment Deadlines and Penalties

You should enroll in a Part D prescription drug plan during your IEP or within 63 days of losing creditable drug coverage from another source. If you go without creditable coverage for 63 consecutive days or more, you may face a late-enrollment penalty calculated as roughly 1% of the national base beneficiary premium for each uncovered month. That base premium is set annually, and the penalty is permanent and added to your Part D premium for as long as you have coverage. Verify the current base amount at Medicare.gov.

Recent Inflation Reduction Act changes reshaped Part D: the coverage-gap “donut hole” structure was replaced, and there is now an annual cap on what you pay out of pocket for covered Part D drugs — $2,000 in 2025, with the cap indexed upward for later years, so confirm the 2026 amount. The maximum allowed Part D deductible is also set each year. Learn more in our Part D donut hole article, and always check the current figures for your plan year.

What Medicare Costs in 2026

Here are recent reference figures — confirm the current amounts at Medicare.gov:

• Part B premium: about $202.90 per month (standard) for 2026; higher-income beneficiaries pay more via IRMAA.
• Part B deductible: about $283 for the year in 2026.
• Part A premium: $0 for most people who paid Medicare taxes for at least 10 years.
• Part A hospital deductible: about $1,736 per benefit period in 2026, with daily coinsurance for longer stays (roughly $434/day for days 61–90 and $868/day for lifetime reserve days 91–150).
• IRMAA: an income-related surcharge added to Part B and Part D for higher earners, based on your modified adjusted gross income from a prior tax year. The thresholds and surcharge amounts change annually, so check your bracket at Medicare.gov or SSA.gov.

Key Dates Calendar for Medicare Enrollment

January 1 to March 31: General Enrollment Period and Medicare Advantage Open Enrollment Period. Your IEP: seven months centered on your 65th birthday month. Medigap OEP: six months starting the first day of the month you are 65 and enrolled in Part B. October 15 to December 7: Annual Election Period for the next year’s Medicare Advantage and Part D changes. Year-round: Special Enrollment Periods triggered by qualifying life events. Confirm exact dates for your year at Medicare.gov.

Frequently Asked Questions

What if I am still working at 65 with employer coverage?

If your employer has 20 or more employees, you can generally delay Part B without penalty as long as you remain covered by the active-employment group plan. Many people still sign up for premium-free Part A. When the employment or coverage ends, you get an eight-month SEP to enroll in Part B penalty-free. Rules for smaller employers and retiree or COBRA coverage differ, so verify your situation with Medicare or SSA.

Can I enroll in Medicare Advantage during my IEP?

Yes. You can join a Medicare Advantage plan during your IEP as an alternative to Original Medicare with Medigap. Note that once you are enrolled in Advantage, buying a Medigap policy later may require medical underwriting in most states unless you have a guaranteed-issue right. Learn about the tradeoffs in our Medicare Advantage vs Supplement guide.

How do I actually sign up for Medicare?

You can enroll online at SSA.gov, by calling Social Security at 1-800-772-1213, or by visiting your local Social Security office. If you are already receiving Social Security benefits before 65, you are generally enrolled automatically in Parts A and B, and your Medicare card arrives about three months before your 65th birthday. For plan questions, call 1-800-MEDICARE.

What is the penalty for late Part B enrollment?

The Part B late-enrollment penalty is 10% of the standard premium for each full 12-month period you were eligible but not enrolled without creditable coverage, and it is added to your premium for as long as you have Part B. For example, delaying two full years could raise your premium by 20% permanently. Because the base premium changes each year, the dollar impact changes too — check the current figures at Medicare.gov.

Take Action Before Deadlines Pass

The most important step is to mark your enrollment deadlines on your calendar and start comparing plans at least a couple of months before your window opens. Contact your State Health Insurance Assistance Program (SHIP) for free, personalized counseling, and use the Medicare.gov Plan Finder to compare Advantage, Part D, and Medigap options in your area. The cost of missing a deadline — through penalties or coverage gaps — far exceeds the time it takes to enroll correctly. For additional Medicare planning resources, explore our healthcare policy guide and our Medigap plans overview, and confirm every date and dollar figure at Medicare.gov before you act.

Sources

• Medicare.gov (Centers for Medicare & Medicaid Services) — 2026 Medicare costs (standard Part B premium $202.90, $283 Part B deductible, $1,736 Part A deductible per benefit period, and daily coinsurance for days 61–90 and 91–150), enrollment-period rules, and the Plan Finder
• Centers for Medicare & Medicaid Services (CMS) — enrollment periods (IEP, GEP, AEP, MA OEP, SEPs), late-enrollment penalties, IRMAA structure, and Inflation Reduction Act Part D out-of-pocket cap
• Social Security Administration (SSA) — enrolling in Parts A and B, automatic enrollment for those already receiving benefits, and the income-related adjustment (IRMAA); SSA 1-800-772-1213, Medicare 1-800-MEDICARE