What the October 15 to December 7 window actually lets you change, the Medigap underwriting rule that makes one choice nearly permanent, and a 2026 cost comparison of both lanes.
Medicare open enrollment runs from October 15 to December 7, and whatever you choose in that window takes effect on January 1. Two separate decisions sit inside it. The first is which lane you are in: Original Medicare, usually paired with a Medigap policy and a stand-alone drug plan, or a Medicare Advantage plan that bundles everything. The second is which specific plan inside that lane. The second decision should be revisited every single year, because drug formularies and provider networks change annually. The first decision deserves more care than it usually gets, because in most states it is far easier to move into Medicare Advantage than to move back out.
If you do only one thing during the window, re-run your own prescription list against next year’s drug plan. That is where the avoidable money is.
What the window actually lets you change
Medicare.gov sets out several separate enrollment periods, and they permit different things. Mixing them up is the most common reason people find themselves stuck with a plan they did not want.
| Period | Dates | What you may do |
|---|---|---|
| Open enrollment, sometimes called the annual enrollment period | October 15 to December 7 | Switch between Original Medicare and Medicare Advantage, change Advantage plans, join, change or drop a Part D drug plan. Coverage starts January 1 |
| Medicare Advantage open enrollment | January 1 to March 31 | Only if you are already in an Advantage plan: change to a different Advantage plan or return to Original Medicare. Coverage starts the first of the month after the plan receives the request |
| Medigap open enrollment | The six months beginning the first day of the month you are 65 or older and enrolled in Part B | Buy any Medigap policy sold in your state at the standard price regardless of your health |
Notice what the second row does not include. The January to March window lets you leave an Advantage plan and return to Original Medicare. It does not give you the right to buy a Medigap policy to go with it. Those are different rules under different laws, and that gap is the single most expensive misunderstanding in Medicare.
The one-way door most people are never warned about
Medicare.gov states the Medigap open enrollment period lasts six months, beginning the first day of the month in which you are both 65 or older and enrolled in Part B. During those six months an insurer may not refuse you or charge you more because of your health. After it closes, there is no federal guarantee that any insurance company will sell you a Medigap policy at all, and if one will, it may cost more because of past or present health problems.
Federal guaranteed issue rights exist, but they are narrow. According to Medicare.gov they cover situations such as your Medicare Advantage plan leaving Medicare or no longer serving your area, an involuntary loss of Medigap coverage, or leaving a Medicare Advantage plan within a defined trial period, and applications generally must be made within 60 days before or 63 days after the triggering event.
State law can be more generous. A KFF analysis published in 2018 found that only four states guaranteed access more broadly for beneficiaries aged 65 and over: Connecticut, Massachusetts and New York with continuous open enrollment, and Maine requiring insurers to issue Plan A during one month each year. Three further states allowed switching around a birthday or policy anniversary, California and Oregon within 30 days of a birthday and Missouri within 30 days of the policy anniversary. State rules change, so confirm the current position with your own state insurance department or State Health Insurance Assistance Program rather than assuming.
The practical consequence is asymmetric risk. Moving from Original Medicare with a Medigap policy into Medicare Advantage is straightforward at any annual enrollment. Moving back years later, after a diagnosis, may leave you on Original Medicare with no cap on your 20 percent Part B coinsurance and no Medigap policy available to cover it. That is not an argument against Medicare Advantage. It is an argument for making the lane decision deliberately at 65 rather than drifting into it at 74.
The two lanes, priced with 2026 figures
These are the published 2026 amounts. The Centers for Medicare and Medicaid Services set the standard Part B premium at 202.90 dollars a month, an increase of 17.90 dollars, with a Part B annual deductible of 283 dollars. The Part A inpatient hospital deductible is 1,736 dollars per benefit period, with coinsurance of 434 dollars a day for days 61 to 90 and 217 dollars a day for days 21 to 100 in a skilled nursing facility. For Part D in 2026, the maximum annual deductible a plan may charge is 615 dollars and the annual out-of-pocket cap on covered drugs is 2,100 dollars, after which covered drugs cost nothing for the rest of the year.
Below is the same person, priced both ways, for one year. Assume a 68-year-old on four generic medications and one brand-name drug, with roughly 3,000 dollars of covered drug costs, who sees specialists twice and has no hospital stay. Plan premiums vary enormously by state, so the Medigap and Advantage premiums here are illustrative placeholders rather than quotes.
| Annual cost item | Original Medicare plus Medigap plus Part D | Medicare Advantage with drug coverage |
|---|---|---|
| Part B premium | 2,434.80 dollars | 2,434.80 dollars |
| Plan premium | Medigap at 180 dollars a month, 2,160 dollars, plus a drug plan at 40 dollars a month, 480 dollars | 0 dollars on a zero-premium plan |
| Part B deductible and coinsurance | Covered by most Medigap letters after the 283 dollar deductible | Copays per visit, perhaps 0 to 50 dollars each |
| Drug costs | Up to 615 dollar deductible, then cost sharing, capped at 2,100 dollars | Same statutory cap of 2,100 dollars, different tiers |
| Realistic total for this year | Roughly 5,900 to 6,500 dollars, highly predictable | Roughly 2,800 to 4,000 dollars, less predictable |
| Worst realistic year | Barely moves, which is the point | Up to the plan out-of-pocket maximum, commonly several thousand dollars |
Read the last two rows together, because that is the actual trade. Medicare Advantage is usually cheaper in an ordinary year. Original Medicare with a Medigap policy costs more every year and is far more stable in a bad one. You are choosing between a lower average and a lower ceiling, and the right answer depends on whether an unpredictable five thousand dollar year would be an inconvenience or a crisis.
Part D is the part that changes underneath you
Drug plans revise their formularies, tier placements and pharmacy networks every year, and plans are required to send an Annual Notice of Change before the enrollment window opens. Most people file it unread. The three things worth checking take about fifteen minutes:
- Is every drug you take still on the formulary, and in the same tier? A drug moved from tier two to tier three can double your share of the cost while the premium stays the same.
- Is your pharmacy still preferred? Many plans have both standard and preferred in-network pharmacies, and the difference in copay between them is real.
- Has a new prior authorisation or step therapy requirement appeared? The drug is technically covered, but you may have to fail a cheaper alternative first.
Two structural improvements are now in place and worth knowing. The Inflation Reduction Act eliminated the old coverage gap and removed cost sharing in the catastrophic phase, so once you reach the annual out-of-pocket cap, covered drugs cost nothing for the remainder of the year. And the Medicare Prescription Payment Plan lets you spread your out-of-pocket drug costs across monthly payments instead of absorbing a large bill in January, which does not reduce the total but makes it survivable. You have to opt in.
What the extra benefits are worth, honestly
KFF reported that more than half of eligible Medicare beneficiaries, 55 percent, or 35.2 million of 64.2 million people, were enrolled in Medicare Advantage in 2026, and that the average beneficiary could choose among 32 Medicare Advantage plans that include drug coverage, out of 3,373 plans available nationally, a 9 percent decrease from 2025. KFF also found that UnitedHealth Group accounted for 26 percent of Medicare Advantage enrollment in 2026 and Humana 20 percent.
KFF noted that virtually all 2026 Medicare Advantage plans advertise extra benefits such as dental, vision and hearing coverage. The honest way to value those is to read the allowance, not the headline. A dental benefit is frequently an annual dollar allowance rather than insurance, and a 1,000 dollar allowance does not cover a crown. Ask three questions: what is the annual maximum, which services count, and which local providers accept it.
The other side of the ledger is utilisation management. Advantage plans use networks and prior authorisation in ways Original Medicare largely does not. Before enrolling, confirm that your actual doctors, your hospital and any specialist you rely on are in network for next year, not this year, and understand that a denial is appealable. Our guide to what to do when an insurance claim is denied covers that process, and it applies here.
For anyone weighing where to seek care under a network plan, our comparison of urgent care, the emergency room and telehealth is worth reading alongside the plan documents, because the cost differences between those settings are usually larger than the differences between plans.
The surcharge that catches higher earners
Part B and Part D premiums are income-adjusted. CMS states that the income-related monthly adjustment amount begins in 2026 when modified adjusted gross income exceeds 109,000 dollars for an individual or 218,000 dollars for a couple filing jointly, and it rises through six brackets from there.
Two details cause most of the surprise. The determination uses your tax return from two years earlier, so 2026 premiums generally reflect 2024 income. And the surcharge is a cliff, not a ramp: a single dollar over a threshold moves you into the whole next bracket. If your income dropped because of a life-changing event such as retirement, the death of a spouse or the loss of a pension, the Social Security Administration accepts a request for reconsideration on Form SSA-44 with documentation. Many people who qualify never file it.
This is also the reason to stop health savings account contributions before Medicare begins. Once you are enrolled in any part of Medicare you may no longer contribute, though you may still spend the balance tax-free on qualified expenses, including Part B and Part D premiums. Our guide to how health savings accounts work explains the timing, and the six-month lookback on Part A enrollment makes it worth getting right.
Free help that is not a sales call
Every state operates a State Health Insurance Assistance Program, funded by the federal Administration for Community Living, which provides free one-to-one counselling from people who are not paid on commission. Medicare also operates a telephone line and the official Plan Finder, which is the only tool that prices next year’s plans against your own drug list.
Two assistance programs are widely under-claimed. Extra Help, formally the Part D Low-Income Subsidy, reduces or eliminates drug premiums and cost sharing for people with incomes up to 150 percent of the federal poverty level. Medicare Savings Programs, run by state Medicaid agencies, can pay the Part B premium entirely, which is worth 2,434.80 dollars a year at the 2026 standard rate. Both have asset tests and both are worth checking even if you expect to be over the limit, because the counted income and assets are narrower than people assume.
A decision rule
If you are newly eligible and within your six-month Medigap window, treat this as the one time you can choose either lane freely. Choose Medigap if a bad year would be financially destabilising, if you travel or spend part of the year in another state, or if you see specialists at a particular academic medical centre. Choose Medicare Advantage if the premium difference is money you need now, your doctors are solidly in network, and you are comfortable with prior authorisation.
If you already have Medicare Advantage and are happy with it, compare it against next year’s version of itself, not against Original Medicare. The plan you renew without reading is a different plan than the one you bought.
If you already have Original Medicare with Medigap, keep the Medigap policy and shop only the drug plan. Dropping Medigap is the decision that cannot reliably be undone.
If your income is near an income-adjustment threshold, check the 2024 figure that will determine your 2026 premium before you do anything else, because it may be worth more than any plan switch.
For the employer and marketplace version of this annual exercise, our guide to the open enrollment mistakes that cost you all year covers different ground, since the rules and deadlines are not the same.
The part nobody enjoys
Medicare is administratively hostile in a way that is not accidental. Plan documents are long, the differences that matter are buried in the summary of benefits rather than the advertising, and the two people most willing to help you compare options are a commissioned broker and a relative who is certain their plan is the best one. Neither is a substitute for putting your own drug list and your own doctors into the official Plan Finder for about half an hour.
The choice is also not permanent in one direction and close to permanent in the other, and no amount of careful reading changes that asymmetry. Knowing which way the door swings before you walk through it is most of the useful advice anyone can give.
Where these figures come from
- Centers for Medicare and Medicaid Services, 2026 Medicare Parts A and B premiums and deductibles fact sheet
- Centers for Medicare and Medicaid Services, Contract Year 2027 Medicare Advantage and Part D final rule fact sheet
- Medicare.gov, joining a plan, and when to buy a Medigap policy
- KFF, Medicare Advantage in 2026: Enrollment Update and Key Trends
- KFF, Medicare Advantage 2026 Spotlight: A First Look at Plan Offerings
- KFF, Medigap Enrollment and Consumer Protections Vary Across States, 2018
- National Council on Aging, 2026 Medicare out-of-pocket costs summary of CMS Part D parameters
- Social Security Administration, Form SSA-44, Medicare income-related monthly adjustment amount life-changing event
General information, current as of September 2026, and not personalised insurance advice. Premiums, formularies and state Medigap rules change every year; confirm the current figures with Medicare or your State Health Insurance Assistance Program before enrolling.
