A front desk lead at a three-physician internal medicine practice told us last week that January had felt like two Januaries. The usual wave of new cards after the fall Annual Enrollment Period, and then a second wave of Medicare patients who did not know what plan they were on. Several had received letters in October saying their Medicare Advantage plan would not be offered in 2026. Some had chosen a new plan. Some had been moved to a different plan from the same insurer. A few had done nothing and reverted to Original Medicare without realizing it, and one of those had a Medigap policy she had cancelled in 2019.
That second wave is what makes the Medicare Advantage open enrollment period 2026 worth a specific plan. The period itself is not new. Since 2019, Medicare Advantage enrollees have had a window from January 1 to March 31 each year to make one change: switch to a different Medicare Advantage plan, or drop Medicare Advantage and return to Original Medicare with or without a Part D drug plan. What is new is the scale of disruption going into it. Insurers exited plans and counties for 2026 at a pace the program had not seen, UnitedHealth said in the fall that it expected to lose about a million Medicare Advantage members in 2026, and enrollment growth across the program slowed to a fraction of its historical rate.
This is the plan we are running with practices this quarter: what the period allows, how to find the patients whose coverage changed, what to do about authorizations issued under a plan that no longer exists, and how to handle patients who landed back in Original Medicare without a supplement.
Key takeaways
- The Medicare Advantage Open Enrollment Period runs January 1 to March 31, 2026; enrollees may switch MA plans once or return to Original Medicare, but people on Original Medicare cannot join an MA plan during it.
- 2026 follows an unusually large wave of plan and county exits, so more patients than usual are on a plan your system does not have on file.
- A change made during the period takes effect the first of the following month, so a patient can be on one plan in February and another in March.
- Authorizations issued by a terminated plan do not automatically transfer; the new plan has its own rules and most require a new request.
- Patients who fell back to Original Medicare without a Medigap policy now owe the $283 Part B deductible and 20 percent coinsurance with no secondary.
What the period allows
The Medicare Advantage Open Enrollment Period (MA OEP) is separate from the fall Annual Enrollment Period that ran October 15 to December 7, 2025. During the MA OEP a person enrolled in a Medicare Advantage plan on January 1 may make one change: move to a different MA plan (with or without drug coverage), or disenroll to Original Medicare and, if they wish, join a standalone Part D plan. They cannot use it to move from Original Medicare into Medicare Advantage, and they cannot switch standalone Part D plans if they were never in MA. The change takes effect on the first day of the month after the plan receives the request. A patient who switches on February 10 is on the new plan March 1.
People whose plan terminated at the end of 2025 also had a Special Enrollment Period that ran from December 8 through the end of February, which gives them slightly more room. And anyone who returns to Original Medicare after their plan was discontinued has a guaranteed issue right to buy certain Medigap policies for a limited window, which matters for the patients we describe below. Beyond that, patients with dual Medicare and Medicaid eligibility or a low-income subsidy can change plans quarterly under their own rules, so a portion of your panel is always moving.
Why 2026 is different
Plan exits happen every year. For 2026 they happened at scale, with several of the largest carriers trimming plans and county footprints and a few regional plans leaving the market. Beneficiaries in the affected plans received a notice by early October and had to choose a new plan during the Annual Enrollment Period or be defaulted, either into another plan from the same insurer where one was available or into Original Medicare where it was not.
For a practice, that means three groups of patients. Those who actively chose a new plan, whose cards are probably right and whose records in your system are probably wrong. Those who were moved to a successor plan and may not know it, whose cards may not have arrived, and whose authorizations were issued under a plan ID that no longer exists. And those who did nothing and are now on Original Medicare, some with a Medigap policy they bought under the guaranteed issue right and some without. The third group is the one that generates the surprise balances.
| Patient situation | What your eligibility check shows | What to do |
|---|---|---|
| Chose a new MA plan in the fall | Old plan on file returns inactive; new plan not on file | Update the payer and member ID; re-verify copays; check whether referrals are required under the new plan |
| Defaulted into a successor plan from the same insurer | Old plan ID inactive; new plan ID under same payer name | Update the plan and member ID; confirm network status for each provider; re-request open authorizations |
| Fell back to Original Medicare with Medigap | MA plan inactive; Medicare Part B active; supplement may not show in HETS | Bill Medicare as primary; ask for the Medigap card; confirm crossover |
| Fell back to Original Medicare without a supplement | MA plan inactive; Medicare Part B active; no secondary | Explain the $283 deductible and 20 percent coinsurance; give an estimate; mention the Medigap guaranteed issue window |
| Switched during the MA OEP | Coverage changes on the first of the month after the request | Re-run eligibility the day before every visit through April 1 |
Finding the patients whose coverage changed
Do not wait for them to arrive. Run a batch eligibility check against every patient on the schedule for the next two weeks who has a Medicare Advantage plan on file, and repeat it weekly through the end of March. The 271 response for a terminated plan comes back with the coverage inactive, and for most payers it will not tell you where the patient went. For that, run the HETS Medicare eligibility check: it returns whether the beneficiary is in an MA plan and, if so, the plan's contract number and name, or shows Part B fee-for-service if they are back in Original Medicare.
Then look backward. Pull every claim denied since January 1 with CO-27 (expenses incurred after coverage terminated), CO-31 (patient cannot be identified as our insured) or CO-22 (coordination of benefits). A cluster of these against a single MA plan is the exit wave showing up in your remits. Each of those claims needs the new payer identified and the claim rebilled, and timely filing runs from the date of service, so the January claims need to move by spring.
Authorizations and referrals that died with the plan
An authorization is issued by a plan to its member for a specific service in a specific window. When the plan terminates, the authorization is no longer honored by anyone. The successor plan, even from the same insurer, is a separate contract with its own utilization management rules, and most treat the patient as new. Some insurers announced transition policies for members moved between their own plans, honoring existing authorizations for a period of 90 days or through the end of a course of treatment. Do not assume. For every patient with an open authorization from a terminated plan, call the new plan, ask whether the authorization will be honored and for how long, and document the answer with a reference number. If not, submit a new request now, because the procedure date is not going to wait for the answer.
Referrals have the same problem in HMO products. A patient defaulted from a PPO to an HMO now needs a primary care referral for the specialist visit they already had scheduled. When the eligibility check shows a plan change, the workflow has to include a check of the new plan's referral and authorization rules, not just a member ID update. Practices that track authorizations in a log rather than in individual charts can sort by plan and see the whole exposure in one view. Our denial management team is handling exactly that sort for several practices this quarter.
The patients who landed on Original Medicare with no supplement
This group needs a conversation, not just a record update. A patient who had a Medicare Advantage plan with a $0 primary care copay and a $40 specialist copay now has Original Medicare: a $283 Part B deductible for 2026, then 20 percent coinsurance on almost everything, with no out-of-pocket maximum. Many of them do not know it. The first sign is a statement for $128 after a visit that used to cost nothing, and the phone call that follows is not pleasant for anyone.
Tell them at scheduling or at check-in. "Our records show your Medicare Advantage plan ended December 31 and you are now on Original Medicare. That means today's visit will apply to your Part B deductible, which is $283 for 2026. Here is an estimate." Then mention two things your staff should know exist: beneficiaries whose plan was discontinued have a guaranteed issue right to buy certain Medigap policies within a limited window, and the State Health Insurance Assistance Program (SHIP) offers free counseling on those choices. Your staff should not advise on which policy to buy. They should point the patient to SHIP or a broker before the window closes.
One more check that is easy to miss: whether you are in network with the plan the patient landed on. A successor plan may have a narrower network than the one that terminated. Confirm each provider's participation status with each new plan ID that appears on your schedule, and if a plan you are not contracted with shows up repeatedly, raise it as a credentialing and enrollment question now rather than in the fall.
Questions we hear
A patient wants to switch plans during the open enrollment period. Can we help them?
You can tell them the period exists, that it runs through March 31 and that they can make one change, and you can point them to Medicare's plan finder or to SHIP counseling. Your staff should not recommend a specific plan. If the patient asks which plans you accept, answer that factually from your contract list, because it is a legitimate factor in their decision.
The old plan and the new plan are both from the same insurer. Do we really need a new authorization?
Ask the new plan and write down the answer. Some insurers honor authorizations across their own plans for a transition period; others do not; and the answer can differ by product. The cost of asking is a phone call. The cost of assuming is a denied procedure.
How long will this keep happening?
Through April 1, when the last MA OEP changes take effect, and then at a lower level all year for dual-eligible and subsidy patients who can change quarterly. The weekly batch eligibility run for Medicare Advantage patients should stay on the calendar through the end of March at least, and honestly, most practices should keep it permanently.
What to do this week
- Run a batch eligibility check on every Medicare Advantage patient scheduled in the next two weeks, and a HETS check on every one whose plan returns inactive.
- Pull all claims since January 1 denied CO-27, CO-31 or CO-22 against Medicare Advantage plans, identify the new payer and rebill.
- List every open authorization issued by a plan that terminated December 31 and call each successor plan to confirm whether it will be honored.
- Give the front desk a script for patients who reverted to Original Medicare, with the $283 deductible, an estimate and the SHIP contact.
- Confirm your providers' network status with each new plan ID that has appeared on the schedule since January 1.
