Patients Switching Medicare Plans This Fall Will Show You the Old Card in January. The Claim Goes to the Wrong Payer.

Medicare's annual election period opened on October 15 and closes on December 7. In those eight weeks a patient can move from Original Medicare to a Medicare Advantage plan, from one Medicare Advantage plan to another, or back to Original Medicare. Under 42 CFR 422.68, every one of those changes takes effect on the first day of the next calendar year. For 2027, that is January 1.

Patients make these choices at home, with a broker or on the phone. Very few call their doctor's office to report it. So in the first week of January, the front desk checks in a familiar face, sees a card already on file and books the visit to the payer that covered the patient in December.

One visit, two possible payers

Here is a hypothetical case. A patient has been in Original Medicare for years, seen every three months for diabetes. In November she enrolls in a Medicare Advantage PPO for 2027. On January 6 she comes in for her regular visit. Nobody asks whether anything changed, the old red, white and blue card is in her chart, and the claim goes to the Medicare Administrative Contractor (MAC).

From January 1, the plan, not Original Medicare, is responsible for her Part A and Part B services. The MAC claim comes back unpaid, and by the time someone notices, the visit is weeks old. If the plan requires a referral or prior authorization for any service in that visit, the chance to get it in advance has already passed. The same thing happens in reverse when a patient leaves a Medicare Advantage plan for Original Medicare, or moves between two plans with different rules.

What Medicare's own eligibility check tells you

This is the easy part to fix, because the information is already there. CMS's guide to checking Medicare eligibility says that for a Medicare Advantage enrollee, the eligibility response shows the patient's plan, the plan enrollment effective and termination dates, and plan contact information, and it tells providers to direct the eligibility query to that plan. A check run for a January date of service will show a plan that starts on January 1, even if the card in the chart is from last year.

The catch is timing. An eligibility check run in December for a January appointment may not reflect a change the patient made late in the election period. The safest check is the one run on, or just before, the actual date of service.

The 90-day rule for patients in the middle of treatment

The harder case is a patient who is partway through a planned course of treatment when the new plan starts. Since 2024, 42 CFR 422.112(b)(8) requires Medicare Advantage coordinated care plans to give a minimum 90-day transition period for any active course of treatment when an enrollee joins the plan after starting that treatment, even if the provider is out of network. During that period the plan must not disrupt the treatment or require reauthorization. The rule covers patients new to the plan and patients new to Medicare.

The definitions matter. A course of treatment is one ordered ahead of time for a specific patient and condition, decided with the patient and the provider. An active course of treatment is one the patient is actively attending and following. A practice that can show the order, the plan of care and the visits already completed is in a much stronger position when a new plan's staff ask for a fresh authorization in January.

Ninety days is a transition period, not a permanent exemption. If treatment will run past it, the practice still needs to meet the new plan's rules in time, and the work of finding out what those rules are is better done in early January than in late March.

January is not the only month

A patient who is already in a Medicare Advantage plan can make one more change between January 1 and March 31, either to another plan or back to Original Medicare. Under the same regulation, that change takes effect on the first day of the following month. So a patient's payer can change again on February 1, March 1 or April 1. A one-time January clean-up of the insurance on file does not cover it.

A front-desk check for the new year

This is general information, not legal advice. A practice can start with these steps:

• From now to December 7, add one question at every check-out for a Medicare patient: "Are you changing your Medicare plan for next year?" Write any answer in the account notes with the new plan's name.
• For every appointment from January 4 to the end of April, run the eligibility check against the date of service, not the date the visit was booked, and compare the plan in the response with the plan on file.
• Ask every Medicare patient for the card they are using this year, scan it, and retire the old card in the chart instead of leaving both.
• Before January 1, list your patients in an ordered course of treatment (therapy, infusions, a planned series of injections) and keep the order, plan of care and visit dates ready to send to a new plan.
• If a new Medicare Advantage plan asks for reauthorization of an active course of treatment within its first 90 days, ask the plan to apply its transition period under 42 CFR 422.112(b)(8), and record the name and date of the call.
• Each week in January, pull claims denied or rejected for coverage or eligibility reasons and correct the payer before the same patient's next visit is billed.

Ask the question before the claim does

None of this is a new rule. The election period, the January 1 effective date and the 90-day transition period are all already in place. What costs practices money is the gap between a patient's choice in November and the moment the office finds out, usually from a denial. One question at check-out and an eligibility check on the date of service close most of that gap. If you want to see how many of last January's denials were wrong-payer or eligibility denials, a revenue review can look at that for one payer and one quarter.