Educational content only. Not Medicare, insurance, or financial advice. Not affiliated with CMS, Medicare.gov, or SSA.
By Keith Guirao, founder and editor of Savvy Senior Central (Maven Media).
Miss a Medicare enrollment window and you do not get a one-time late fee. Medicare.gov states that late enrollment penalties are added to your monthly premium, are not a one-time late fee, and for Part B and Part D are usually charged for as long as you have that coverage. You can also wait months with no coverage. That is the federal design.
The ads treat enrollment as a shopping season. Medicare.gov treats it as named periods plus qualifying-event exceptions. Plan choice can be revisited most years. The enrollment *date* for Part B often cannot.
I have spent 18 years inside consumer marketing and lead generation in insurance and health. That is operator experience, not a counseling credential. This page is the 2026 calendar and penalty math as CMS and Medicare.gov print them, not a recommendation to enroll, delay, or switch.
You enroll in Part A and Part B through Social Security (or the Railroad Retirement Board for railroad retirees). CMS runs the program; SSA takes the applications. You join or switch an Advantage or Part D plan with the plan or at Medicare.gov. Those are different desks.
First fork: automatic enrollment or silent nothing
If you are already receiving Social Security or Railroad Retirement benefits before 65, you are generally enrolled in Part A and Part B automatically, and the card arrives in the mail. Everybody else has to apply. Nothing arrives. Nothing prompts. The window still closes on schedule.
Because full Social Security retirement age is now later than 65 for people reaching it today, fewer people are automatically enrolled than folklore suggests. Assuming a card will turn up is one of the most expensive assumptions in this area.
Anyone automatically enrolled who is still working with large-employer coverage and wants to delay Part B must actively decline Part B, following the instructions that come with the card. Part A generally stays.
Initial Enrollment Period (IEP): seven months, file early if you want day-one coverage
Your first chance to sign up for Part A and Part B is generally a 7-month window: 3 months before the month you turn 65, your birthday month, and 3 months after. Medicare.gov: coverage always starts on the first of a month.
If you qualify for premium-free Part A, Part A coverage typically starts the month you turn 65 (the month before, if your birthday is the first of the month). Part B (and premium Part A, if you must buy it) starts based on when you sign up:
| If you sign up | Coverage starts |
|---|---|
| Before the month you turn 65 | The month you turn 65 |
| During your birthday month, or in the 3 months after | The next month |
Filing in the birthday month feels natural. Filing in the first three months is usually safer if you want coverage active without a gap, because processing, not the birthday cake, drives the start date.
You can sign up for premium-free Part A any time after you turn 65; coverage can go back up to 6 months from when you sign up, but not earlier than the month you turned 65.
You can join a Medicare Advantage plan during IEP if you have Part A and Part B. You need Part A or Part B to join a drug plan. If you joined Advantage during IEP, you can change plans or return to Original Medicare within the first 3 months you have A and B.
Miss IEP without a Special Enrollment Period and you may wait, go without coverage, and owe a late-enrollment penalty.
Three ways to file Part A and Part B
- Online at SSA.gov. Fastest for a straightforward application; save the confirmation number.
- By phone with Social Security. Practical when employer coverage or a Special Enrollment Period is involved.
- In person at a Social Security office (appointment; useful when forms and employer verification must travel together.
When you enroll from an employer plan, paperwork matters. Medicare.gov: Part B coverage during the employment-related Special Enrollment Period generally starts the month after Social Security or the Railroad Retirement Board receives completed forms, and an extra form showing you had job-based coverage while you or your spouse were working is required. That is an employer signature. Start it before the month you need coverage. Keep copies. Penalty disputes are decided on evidence.
General Enrollment Period (GEP): January 1-March 31
If you missed IEP and do not qualify for a Special Enrollment Period, you can sign up for Part B during GEP each year (January 1-March 31). You can also buy Part A during GEP if you do not qualify for premium-free Part A and missed IEP. You may pay a higher premium for late enrollment.
2026 coverage start rule: Medicare.gov and *Medicare & You 2026* say coverage starts the first day of the month after you sign up. Enrolling in January means coverage from February 1. Older materials (including some still-circulating CMS booklets) still say July 1. Prefer the live Medicare.gov page. The late enrollment penalty still attaches either way.
GEP is not the same window as Medicare Advantage Open Enrollment, even though both run January 1-March 31. GEP is for people who still need Part B (and maybe to buy Part A). Advantage Open Enrollment is only for people already in an Advantage plan.
Annual Open Enrollment (AEP): October 15-December 7
Open Enrollment runs October 15 through December 7. Changes are effective January 1 of the next year if the plan gets your enrollment request by December 7.
During AEP you can:
- Join, drop, or switch Advantage plans (with or without drug coverage)
- Switch Original Medicare ↔ Advantage
- If you have Original Medicare, join, drop, or switch a Part D plan
If you switch to Original Medicare, you may need a separate drug plan, and you may want Medigap. Medigap Open Enrollment is a different, generally one-time six-month window. It is not AEP.
If you keep the coverage you have, you do not have to do anything. It continues.
Medicare Advantage Open Enrollment (OEP): January 1-March 31, already-in-Advantage only
OEP is only for people already in a Medicare Advantage Plan. One change: switch to another Advantage plan, or drop Advantage, return to Original Medicare, and join a separate drug plan. Coverage starts the first of the month after the plan gets your request.
You cannot use OEP to go from Original Medicare to Advantage. That move is AEP, IEP, or a qualifying Special Enrollment Period.
Special Enrollment Periods: qualifying events, not a sales calendar
You can make Advantage and drug-plan changes when certain events happen, for example, you move or you lose other coverage. Timing and allowed changes depend on the event. Medicare.gov’s list is long. It is not a monthly shopping window.
High-level examples (not a complete catalog):
- Move out of a plan’s service area, or to an address with different plan options (often starting when you move, for 2 full months after)
- Lose employer or union coverage, including COBRA, as other coverage (often 2 full months after the month coverage ends, for joining Advantage or a drug plan)
- Lose Medicaid eligibility, or Extra Help changes
- Lose creditable drug coverage
- Have Medicare and full Medicaid, or Extra Help, and can change drug coverage once a calendar month (with limits in some drug-management situations)
- Exceptional situations (disaster, misleading information, incarceration release) can open Part A/B windows; after you sign up for A or B in an exceptional-situation SEP, you generally have 2 months to join Advantage or a drug plan
Part A/B SEP for current employment. If you did not sign up for Part B (or buy Part A) when first eligible because you had group health coverage based on current employment: yours, a spouse’s, or a family member’s if you have a disability, you can sign up any time you are still covered by that group plan, and during the 8-month period that begins the month after employment ends or coverage ends, whichever happens first. Coverage generally starts the first of the month after you sign up.
COBRA and retiree coverage are not coverage based on current employment. Losing those does not start this 8-month clock. Marketplace coverage is not this SEP either. VA coverage does not create a Part B Special Enrollment Period.
If you miss the 8-month employment SEP, you wait for GEP and you might pay a Part B penalty.
Disability-based Medicare with coverage through a family member’s work uses a 100-employee large-group threshold instead of 20. ESRD has separate rules.
Turning 65 while working: employee count decides whether Part B can wait
| Situation at 65 | What Medicare.gov points you toward | Why it matters |
|---|---|---|
| Still working, employer has 20 or more employees | Part A is usually worth taking. Part B can often wait until you or your spouse stop working. | Job-based coverage usually pays first; an 8-month SEP protects you afterward. |
| Still working, employer has fewer than 20 employees | Check with the employer; often sign up for both A and B at 65. | Medicare usually pays first; the job plan may not pay without Part B. |
| Retired, on retiree or COBRA coverage | Sign up at 65. | Neither counts as active job-based coverage for this SEP. |
| On a Marketplace plan | Sign up when first eligible and end Marketplace coverage carefully. | Premium-free Part A eligibility generally ends Marketplace premium help; keeping help can mean repayment at tax time. |
COBRA feels like employer coverage. Medicare.gov is explicit that the 8-month SEP starts when you stop working, even if you choose COBRA. Someone who takes 18 months of COBRA at 65 and assumes the Medicare clock is paused can exhaust the SEP months before COBRA ends.
HSA note: contributions to a Health Savings Account must stop once Medicare begins, and Part A enrollment can be backdated. Confirm timing with your benefits office and tax advisor before filing.
Medigap’s quiet six-month clock
Medigap has its own timing, separate from AEP. The federal open enrollment window for Medigap is generally six months beginning when you are 65 and enrolled in Part B. Inside it, insurers in most situations must sell regardless of health. Outside it (unless your state is more generous or a guaranteed-issue right applies), insurers may medically underwrite and may decline.
That is why the decision at 65 between Original Medicare with a supplement and Medicare Advantage is less reversible than fall open enrollment advertising suggests. Switching from Advantage back to Original is often permitted; buying the supplement that makes Original workable may not be, years later, on the same terms. Check your state insurance department; state rules vary.
What a missed window costs in 2026 figures
| Penalty | How Medicare calculates it | How long it lasts |
|---|---|---|
| Part A (only if you buy it) | Premium may rise 10% | Twice the number of years you did not sign up, then it ends |
| Part B | Extra 10% for each full 12-month period you could have signed up | Generally for as long as you have Part B |
| Part D | Extra 1% of the national base beneficiary premium per uncovered month (after 63+ days without creditable coverage) | For as long as you have Medicare drug coverage, even if you switch plans |
Part B worked example (Medicare.gov, 2026🙂 Wait 2 full years (24 months), no SEP → 20% penalty on the standard premium of $202.90 → $40.58 + $202.90 = $243.48, rounded to $243.50/month. Not for two years. For as long as you keep Part B, rising as the standard premium rises.
Part D worked example (Medicare.gov, 2026🙂 Wait 14 months with no creditable coverage → 14% of the national base beneficiary premium of $38.99 → $5.46, rounded to $5.50/month added to the plan premium. The base premium is recalculated annually, so the dollar penalty can change each year.
Part A buy-in (2026🙂 About 99% pay no Part A premium (40 quarters). If you buy: $311 (30-39 quarters) or $565 (fewer than 30). Example on Medicare.gov: eligible 2 years but did not sign up → pay the higher premium for 4 years. You usually also need Part B to buy Part A.
Generally you will not pay a Part B penalty if you qualify for a Special Enrollment Period or you enroll in a Medicare Savings Program. Generally you will not pay a Part D penalty if you have creditable drug coverage or Extra Help. Keep annual creditable-coverage notices from employer or union plans.
After A and B are in place
Enrollment in Original Medicare is the government step. A drug plan, Medigap policy, or Medicare Advantage plan is a private-market step, bought from an insurer or through Medicare.gov Plan Compare, not completed by filing with SSA alone.
Treat the volume of mail and calls around a 65th birthday as a signal about commissions, not about deadlines. Plan Compare at Medicare.gov carries the same plan data brokers use, priced against your drugs. SHIP counselors give the same help free and are not paid on the outcome.
A from-age-64½ sequence (education, not advice)
- Check your earnings record with Social Security. Confirm 40 quarters, the difference between free Part A and hundreds of dollars a month.
- Establish which window applies. Still working with 20+ employees is the common case where delaying Part B can be safe. Get the employee count from HR in writing.
- Get creditable-coverage letters in writing (health and drug). Keep them.
- If you want coverage without a gap, file in the first three months of IEP, not only the birthday month.
- Decide Original-plus-Medigap vs Advantage before the Medigap six-month clock closes, because that clock starts with Part B and does not reopen as AEP.
This page does not rank carriers or treat a marketplace quote as a CMS figure.
FAQ
Do I enroll with Medicare or with Social Security?
With Social Security (or the Railroad Retirement Board if you are a railroad retiree). CMS runs the program; SSA takes applications and eligibility determinations, including the 40-quarter test for premium-free Part A.
Will I be enrolled automatically at 65?
Only if you are already receiving Social Security or Railroad Retirement benefits before 65. Everybody else must apply. Because full retirement age is later than 65, fewer people are automatic than assume they will be.
If I miss IEP, does coverage still start in July?
Not under the live 2026 rule. GEP remains January 1-March 31. Coverage starts the first of the month after you sign up. Prefer Medicare.gov and *Medicare & You 2026* over older July-start materials. The late enrollment penalty still applies.
Can I use January-March to join Advantage if I have Original Medicare?
No. Advantage Open Enrollment (January 1-March 31) is only if you are already in Advantage, and it is one change. Original → Advantage is AEP (October 15-December 7), IEP, or a qualifying SEP. January-March GEP is for signing up for Part B (and buying Part A if needed), a different window.
Does COBRA let me delay Part B?
No. The 8-month Part B SEP based on current employment starts when you stop working (or lose that job-based coverage), even if you choose COBRA. Do not wait until COBRA ends.
How long does the Part B penalty last?
Usually as long as you have Part B. It is 10% for each full 12-month period you could have signed up but did not. It is not a one-time fee.
Is $38.99 the price of a Part D plan in 2026?
No. $38.99 is the national base beneficiary premium used for late-enrollment penalty math and Part D IRMAA. The 2026 yearly out-of-pocket cap for covered Part D drugs is $2,100.
Where do I actually sign up?
Social Security for Part A and Part B. Medicare.gov or 1-800-MEDICARE for Advantage and Part D. SHIP for free counseling. I am none of those.
Sources
Every figure traces to CMS, Medicare.gov, or SSA. We do not cite insurance marketplaces for data. Figures last verified September 22, 2026 (ET).
- Medicare.gov: When can I sign up for Medicare?
- Medicare.gov: Avoid late enrollment penalties
- Medicare.gov: Joining a plan
- Medicare.gov: Special Enrollment Periods
- CMS: 2026 Medicare Parts A & B Premiums and Deductibles
- CMS: 2026 Part D Bid Information ($38.99 base)
- SSA: ssa.gov enrollment
- Medicare.gov: Medicare & You 2026
- Medicare.gov: Working past 65
