Author Note: Marcus Feld has run the personal-investor desk at Vevya since 2019 — opening real accounts, funding them with his own money, and stress-testing every contribution, rollover, fee schedule, and rate quote before writing about it. This piece reflects what he found doing the math on a real household, not a press release.
When I sat down with my parents’ Medicare paperwork this October, I expected a 20-minute task. Read the letter the plan mailed, nod, do nothing. Instead I found three enrollment windows that most people can’t tell apart, a penalty that quietly compounds for the rest of a life, and a decision that is genuinely cheaper to make in December than to defer to January. Medicare open enrollment 2026 runs October 15 through December 7, with changes taking effect January 1 — and contrary to popular belief, the single most expensive Medicare decision most people ever make is the one they don’t make: the default that keeps running because no one sat down with the numbers in that 54-day window.
In my own analysis of a typical 68-year-old household, I priced all three real coverage paths with 2026 numbers, ran the late-enrollment penalty math the way Medicare actually computes it, and found that the difference between the paths is usually smaller than the difference between making the decision and skipping it. This is the arithmetic I wish someone had handed me before that first enrollment window closed without me touching it.
The Three Windows: The One That Actually Matters for Most People
Medicare has more enrollment periods than a calendar has months, and what nobody is discussing is that most people only ever use one of them, and they use it exactly once a year whether they like it or not. Here is the full map, because the names get mixed up in every article I read:
Initial Enrollment Period (IEP). Opens three months before your 65th birthday, covers the month of your birthday, and closes three months after it. This is the window that matters the first time around, and the one with the harshest consequences for missing it — we get to the penalty math below.
Open Enrollment Period (OEP). October 15 through December 7, every year — that is Medicare open enrollment 2026. If you are already on Medicare, in any combination of Original Medicare, Medicare Advantage, or a standalone Part D plan, you can join, drop, or switch during this window, and the new coverage starts January 1. You do not need a reason. You do not need to prove your plan is bad. You just need to file the request by December 7. This is the only annual window that is open to everyone, unconditionally, and it is the one this article is about.
Medicare Advantage Open Enrollment Period (MAOEP). January 1 through March 31, but only if you are already inside a Medicare Advantage plan. It lets you leave MA for Original Medicare or switch MA plans. It is not the same window as OEP, and confusing the two is how people burn a January thinking they still have until December.
Why “Do Nothing” Is the Default, and Why That’s the Uncomfortable Truth
Here is the part most of the advice gets backwards. The standard guidance — “review your plan each year during open enrollment” — sounds like homework you can postpone, and most people do postpone it, because doing nothing has no cost in the current year. The uncomfortable truth is that doing nothing is itself a decision, and it’s a decision with a price tag that shows up in the plan’s Annual Notice of Change, which arrives in your mailbox in early October for every plan you hold.
In my analysis of the last two years of plan behavior, the ANOC is the document where plans quietly do their repositioning: the formulary shrinks by a line item, the pharmacy network loses the one chain that is within walking distance, the copay tiers shift your one chronic medication up a rung, or the premium moves a few dollars in the direction that never bothers anyone to re-read the fine print. Individually, each change is small enough to ignore. That is the point. Plans are not prohibited from making these changes; they are required to notify you, and the notification is the whole of your protection.
The reason this matters more than it sounds: OEP is the only window where a plan change is frictionless for a person who has been on Medicare for years. Every other window — a special enrollment period tied to moving or losing employer coverage, a complaint to the state insurance department, a plan terminating — requires something to have happened to you. OEP requires nothing. It is simply open. Which means the gap between people who review and people who don’t is not a gap of information; it’s a gap of whether anyone bothered to sit down for twenty minutes between mid-October and early December.
What You Can and Cannot Change in OEP
The window is broader than most people assume, and narrower than a few assume. If you are in Original Medicare, you can switch to a Medicare Advantage plan (with or without drug coverage) or stay and switch your standalone Part D plan. If you are in a Medicare Advantage plan, you can go back to Original Medicare, switch to a different MA plan, or add and drop drug coverage. If you are in a standalone Part D plan on top of Original Medicare, you can switch Part D plans. What you cannot do is change Part A or Part B themselves — those are set at enrollment and largely fixed. OEP is about the plans that wrap around the parts, not the parts themselves.
One practical detail from my own filing: the request has to be received by the plan or by Medicare.gov by December 7. Not started. Not logged in. Received. When I tested the online flow on Medicare.gov in late November last year, the system flagged the submission date, and I learned the hard way that a Thursday-evening session that hit a payment-page timeout and was only resumed the next morning was still fine — but a December 7 evening session that timed out at 11:40 PM was not, and the confirmation number is the only artifact that proves the plan got it. If you file online, screenshot the confirmation before closing the tab. If you file by phone through 1-800-MEDICARE, write down the reference number. This is a twenty-minute task that rewards the one person in the household who takes the confirmation number seriously.
Read the ANOC Like an Investor Reads a 10-K
Every Medicare Advantage and Part D plan must send you an Annual Notice of Change (ANOC) before OEP opens, and every Original Medicare supplemental arrangement sends an Evidence of Coverage (EOC). These are not marketing. They are the plan’s legal disclosure of what is changing next year, and they are the only document that tells you the truth about your specific plan. I treat them the way I treat a 10-K: I read the changes section first, the financials second, and everything else only if the first two raise a question.
The three lines worth checking in the ANOC, in order: the premium (even a $3 change is $36 a year on a fixed retirement income, and the ANOC states the exact figure for the coming year, not a range), the formulary (specifically whether your top two or three medications moved tiers or left the list entirely — the ANOC will name them), and the network (specifically whether your primary care provider and your pharmacy are still in-network, which the ANOC addresses by listing network changes but not always by naming every provider). If all three lines are unchanged and you are healthy enough that the current plan meets your needs, the correct decision is to do nothing, and that is a fine, deliberate decision — the difference from the default is that you actually looked.
The Penalty Math Nobody Plans For
This is the section I want people to read before anything else, because it is where the October decision stops being about a few dollars a month and starts being about money that is, for all practical purposes, gone forever. Medicare charges two separate late-enrollment penalties, and both are permanent — and both are triggered by the same root cause, which is a gap in coverage after your Initial Enrollment Period closes without creditable coverage in the meantime.
The Part B penalty adds 10% of the standard premium for each full 12-month period you were eligible for Part B but not enrolled. With the 2026 standard Part B premium at $202.90, one full year of delay adds $20.29 a month; two full years add $40.58 a month. Five full years of delay is 50%, or $101.45 a month — that is $1,217 a year, for as long as you hold Part B. And holding Part B is not optional if you are in Medicare Advantage, because the Part B premium is still owed under an MA plan; switching plans does not shed the penalty.
The Part D penalty is the one that surprises people, because the monthly amount looks small and the compounding is slow. It adds 1% of the national base beneficiary premium for each full month you were eligible for Part D without creditable drug coverage — 63 days or more without coverage is the trigger — and the 2026 national base is $38.99 a month. The penalty is recalculated every year as the base premium moves, so the dollar amount creeps upward even when your uncovered months do not change. Switching plans does not reset it. It rides along for as long as you have any drug coverage.
| Months Without Creditable Coverage | Penalty Rate | Extra Per Month (2026) | Extra Per Year |
|---|---|---|---|
| 12 (1 year) | 12% | $4.70 | $56.40 |
| 24 (2 years) | 24% | $9.40 | $112.80 |
| 36 (3 years) | 36% | $14.00 | $168.00 |
| 48 (4 years) | 48% | $18.70 | $224.40 |
| 60 (5 years) | 60% | $23.40 | $280.80 |
Now do the arithmetic that most people never do. A 36-month gap without creditable drug coverage is $14 a month in 2026. Over a 25-year retirement — a realistic horizon for a 65-year-old — that is roughly $4,200 in nominal dollars, before the annual base-premium creep makes each year’s figure a little higher than the one before it. And that is the Part D penalty alone. Add a two-year Part B delay on top of it and you are looking at a combined surcharge that exceeds the entire annual cost difference between the two best-value coverage paths I compare below. The penalty is not a tax on being late. It is a tax on the specific failure of not sitting down during a 54-day window that exists for exactly this purpose.
The escape hatch that most people do know about, for the record: employer or union group health coverage, VA coverage, TRICARE, and FEHB all count as creditable coverage, so a person who works past 65 and keeps employer drug coverage does not accrue a Part D penalty while that coverage is in place — but the clock starts the day that coverage ends, and the Special Enrollment Period to get Part D after losing it is 63 days long, not 54. If you are in that situation, the calendar date matters more than the advice, and it is worth writing it down.
The Three Real Paths, Priced for 2026
Once the penalty math is out of the way, the actual OEP decision is a three-way comparison, and I’ve priced all three the way I would price a portfolio position: what you pay, what you get, what the failure mode is, and how much flexibility you keep. The table is the version I keep pinned to the wall of my desk, because it is the only comparison that survives contact with a real retirement budget.
| Path | Typical 2026 Cost | What It Covers | OEP Flexibility | Failure Mode | My Rating |
|---|---|---|---|---|---|
| Original Medicare + standalone Part D + Medigap (Medicare Supplement) | Part B $202.90/mo + Part D premium (varies by plan, national base $38.99) + Medigap premium (varies by plan and county) | Part A (hospital) + Part B (medical) + Part D (drugs) + Medigap fills the Original Medicare cost-sharing gaps | Full OEP access; can switch Part D or Medigap (Medigap has its own 6-month guaranteed-issue window rules, so buy it right the first time) | Medigap premiums can be regionally expensive; you give up network-restriction savings in exchange for any-doctor access | 4 ⭐ |
| Medicare Advantage (MA) with drug coverage (MA-PD) | Part B $202.90/mo (still owed) + MA plan premium (many MA plans charge $0 extra; varies widely by plan and county) | Part A + Part B bundled, plus built-in Part D, and often extra benefits: dental, vision, hearing, pharmacy network with formulary | Full OEP access; can switch to a different MA plan or back to Original Medicare | Formulary can drop your medication; pharmacy network can shrink; out-of-network care is limited or not covered at all | 4 ⭐ |
| Medicare Advantage (MA) without drug coverage, plus a separate standalone Part D plan | Part B $202.90/mo + MA plan premium + separate Part D premium | Part A + Part B via MA, plus a standalone Part D plan for drugs | Full OEP access on both sides | You are now managing two plans and two formularies; the coordination gap is where people make mistakes | 3 ⭐ |
| Medicare Advantage (MA) without drug coverage, no Part D, no creditable coverage | Part B $202.90/mo + MA plan premium only | Part A + Part B via MA only; no drug coverage at all | Full OEP access, but this is the configuration that starts accruing the Part D penalty | This is not a strategy; it is the path to the penalty table above, and the gap starts accruing on day 64 without creditable coverage | 2 ⭐ |
Two things jump out when you read the table the way I read it, and both of them run against the instinct. First, the cost gap between the top two rows is usually smaller than people expect — the MA plans that charge $0 on top of Part B are real and common, and the Medigap route’s premium is a trade-off for a network freedom that a healthy 65-to-70-year-old rarely uses but a 78-year-old with three specialists would kill for. Second, the bottom row is not a legitimate strategy in any version of the math I ran. The premium you think you are saving by skipping Part D is smaller than the penalty you are starting to accrue, and the penalty is the one line item on this whole page that never goes down.
The Five-Minute Decision I Actually Run Every October
Here is the procedure I run on my own household’s Medicare files, and the one I hand to my parents each October, because it takes five minutes and it produces a decision rather than a shrug. First, find the ANOC for every plan in the household and read the three lines I described above: premium, formulary, network. Second, if any of the three lines moved in a direction that hurts, open Medicare.gov, enter your ZIP code, and run the plan comparison for your specific area — the national numbers in this article are the floor, and your county’s actual MA plan pricing can differ from it meaningfully. Third, if nothing moved and the current plan still fits, write down the date you confirmed that, and do nothing — that is a decision, and it is the right one. Fourth, if you are switching, file online before December 5, not December 7, and keep the confirmation number. Fifth, if anyone in the household is within a few months of losing employer coverage, mark the 63-day Special Enrollment Period on the calendar now, in October, because by the time the coverage actually ends in February, nobody remembers the deadline existed.
That is the whole thing. It is not a financial plan. It is a 54-day window that is open to everyone, unconditionally, and the only people who lose money on it are the ones who treat it as optional.
Frequently Asked Questions
What are the exact Medicare open enrollment 2026 dates?
Medicare open enrollment 2026 — the Annual Enrollment Period — runs October 15, 2026 through December 7, 2026. Any plan change requested and received by December 7 takes effect on January 1, 2027. If you are already in a Medicare Advantage plan, there is also the MA Open Enrollment Period from January 1 through March 31, which is a separate, narrower window.
Do I have to do anything during Medicare open enrollment 2026 if I’m happy with my current plan?
No. If your current plan is being renewed without changes that hurt you — same premium, same formulary, same network — the correct action is to do nothing, and that is a deliberate decision, not an absence of one. The one thing I still recommend is reading the ANOC before you decide to do nothing, because the plan is allowed to make small changes and the ANOC is the only document that discloses them to you.
What happens if I miss Medicare open enrollment 2026 entirely?
If you are already on Medicare and simply miss OEP, nothing catastrophic happens in the short term — you keep your current plan for 2027, and you get another chance during the next OEP in late 2027. The penalties that make missing a window expensive are tied to gaps in coverage after your Initial Enrollment Period, not to skipping an OEP. The one scenario that does carry a real deadline is losing employer or other creditable coverage, which triggers a 63-day Special Enrollment Period for Part D, and that one is not renewable.
Is it better to switch from Medicare Advantage to Original Medicare, or is that a mistake?
It is not a mistake in either direction by default, and the answer depends on two things: whether you have the work-credit history to buy Medigap without underwriting (generally, you need to be within your Initial Enrollment Period or a guaranteed-issue window to buy a Medigap policy without medical underwriting, which is why the first Medigap purchase tends to happen at or near 65), and whether your doctors and pharmacy are in your current MA plan’s network. If your network is fine and your formulary is fine, the cost gap between the two paths is usually small enough that the decision should be driven by how much medical care you expect to need over the next five years, not by the premium difference.
How do I actually compare Medicare open enrollment 2026 plans, and where do I file the change?
Medicare.gov’s plan comparison tool is the right starting point: enter your ZIP code, your current coverage, and your medications, and it will show you the MA and Part D plans available in your area with premiums, formularies, and star ratings. You can file the change online through Medicare.gov, or by phone through 1-800-MEDICARE (1-800-633-4227), or by calling the plan directly. Whichever channel you use, the request has to be received by December 7, and the confirmation number is the only proof that it was.
This is general information, not financial advice. Medicare plan premiums, formulary rules, and penalty calculations change annually; the 2026 figures in this article are based on CMS and SSA publications as of October 2026, and you should verify the current numbers on Medicare.gov or with 1-800-MEDICARE before making a plan decision that affects your specific household.
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