Medicare Advantage Open Enrollment Checklist: What You Can Change During OEP — Period

Know Your OEP Deadline: January 1 Through March 31

The Medicare Advantage Open Enrollment Period (OEP) is a specific window from January 1 to March 31 each year that allows current Medicare Advantage enrollees to make one change to their health coverage. This period exists to give beneficiaries who are dissatisfied with their current plan a mid-year opportunity to switch to a different Medicare Advantage plan or return to Original Medicare.

¹ Missing this window means waiting until the Fall Annual Election Period (October 15 to December 7) to make changes, with coverage starting January 1 of the following year.

² Despite this abundance of options, most people do not make changes to their coverage during enrollment periods.³ This inertia can cost thousands in unnecessary premiums, copays, and restricted access to preferred providers.

The OEP is a use-it-or-lose-it opportunity. If you make no changes by March 31, you remain locked into your current plan until the next Fall enrollment window. Mark the deadline on your calendar now — the consequences of missing it are significant.

What the Medicare Advantage Open Enrollment Period Actually Covers

The OEP is exclusively for people already enrolled in a Medicare Advantage plan. It does not apply to beneficiaries on Original Medicare with a standalone Part D drug plan.⁴ During this period, you can make exactly one change: switch to a different Medicare Advantage plan or disenroll from Medicare Advantage and return to Original Medicare with a standalone Part D plan.⁵

This is a critical distinction. The OEP is not a free-for-all enrollment window. You cannot enroll in a Medicare Advantage plan for the first time during OEP — that requires the Fall Annual Election Period or an Initial Enrollment Period. You also cannot switch from Original Medicare to Medicare Advantage during OEP.

The single-change rule means you must choose carefully. If you switch from Plan A to Plan B during OEP, you cannot later switch to Plan C within the same period. Your one change is final until the next enrollment window.

Key Changes You Can Make During OEP — And What You Cannot

Changes you can make during OEP:

• Switch from one Medicare Advantage plan to another Medicare Advantage plan
• Disenroll from Medicare Advantage and return to Original Medicare
• Enroll in a standalone Part D prescription drug plan when returning to Original Medicare

Changes you cannot make during OEP:

• Enroll in a Medicare Advantage plan for the first time
• Switch from Original Medicare to Medicare Advantage
• Switch from one Medigap plan to another Medigap plan
• Enroll in a Medigap plan without medical underwriting (with limited exceptions)

The most common reason beneficiaries use OEP is frustration with network restrictions. Suppose you enrolled in a Medicare Advantage HMO plan during Fall enrollment, only to discover your primary care physician is out of network. During OEP, you can switch to a PPO Medicare Advantage plan that includes your doctor.

Another scenario: imagine you chose a Medicare Advantage plan with a $0 premium but high copays for specialist visits. After a new diagnosis requiring monthly specialist appointments, those copays become unmanageable. OEP allows you to switch to a plan with higher premiums but lower copays.

What you cannot do during OEP is exit Medicare Advantage for a Medigap plan without facing medical underwriting. This is the most misunderstood rule in Medicare enrollment.

How OEP Differs from the Annual Enrollment Period

The Fall Annual Election Period (AEP) runs October 15 to December 7 and is open to all Medicare beneficiaries — those on Original Medicare, Medicare Advantage, and Medigap alike.⁶ The OEP, by contrast, is restricted to current Medicare Advantage enrollees.

The practical difference matters. If you are on Original Medicare and want to try a Medicare Advantage plan, you must wait until the Fall AEP. If you are already on Medicare Advantage and realize it is not working, OEP gives you a mid-year escape hatch.

Consider a retiree who enrolled in a Medicare Advantage plan during Fall enrollment because of the $0 premium and included dental coverage. By February, they discover their preferred hospital is out of network and the dental benefit has a $1,500 annual cap. During OEP, they can switch to a different Medicare Advantage plan with a broader network and higher dental cap.

Coordinating OEP Changes with Your Social Security and Retirement Income

Switching Medicare plans during OEP can affect your monthly budget in ways that interact with Social Security benefits and retirement account withdrawals. Medicare Part B premiums are typically deducted directly from Social Security checks. If you switch from a Medicare Advantage plan to Original Medicare, your Part B premium deduction remains the same, but you now need a separate Part D premium and a Medigap premium.

For a retiree with a $2,000 monthly Social Security benefit, adding a $175 Medigap premium and a $45 Part D premium means $220 in additional monthly deductions. This reduction in net Social Security income may require adjusting your retirement account withdrawal strategy.

Suppose you are taking systematic withdrawals from an IRA to supplement Social Security. A $220 monthly increase in healthcare costs means withdrawing an additional $2,640 per year from your IRA. At a typical 4% withdrawal rate, this requires roughly $66,000 in additional IRA savings to sustain indefinitely.

The coordination works both ways. If you switch from a Medicare Advantage plan with high copays to one with lower cost-sharing, your out-of-pocket medical expenses decrease. This frees up cash flow that can reduce the amount you need to withdraw from retirement accounts each month.

Avoiding Coverage Gaps When Switching Plans Mid-Year

The most dangerous mistake during OEP is creating a gap in prescription drug coverage. When you switch from one Medicare Advantage plan to another, coverage is continuous — the new plan takes over on the first day of the month following your switch. But when you disenroll from Medicare Advantage to return to Original Medicare, you must enroll in a standalone Part D plan simultaneously.

If you disenroll from Medicare Advantage on March 15 and do not enroll in a Part D plan until April 1, you have a 17-day gap in prescription drug coverage. During that gap, you pay full retail price for any medications. Worse, a coverage gap of 63 days or more triggers a late enrollment penalty when you eventually enroll in Part D — 1% of the national base beneficiary premium for each month you went without coverage.⁷

The solution is simple: enroll in your new Part D plan before disenrolling from Medicare Advantage. The effective date of the Part D plan should be the same date your Medicare Advantage coverage ends. Most enrollment systems allow you to coordinate these dates.

For beneficiaries switching between Medicare Advantage plans, the new plan handles the transition. Your prescriptions should remain covered without interruption. But verify this with both plans before making the switch.

IRMAA and Part D: Hidden Costs to Check Before You Switch

Income-Related Monthly Adjustment Amount (IRMAA) surcharges apply to both Part B and Part D premiums for beneficiaries with modified adjusted gross income above certain thresholds. For single filers, IRMAA applies when MAGI exceeds $106,000; for married couples filing jointly, the threshold is $212,000. Switching from a Medicare Advantage plan to Original Medicare with a standalone Part D plan does not change your Part B IRMAA, but it does expose you to Part D IRMAA.

Medicare Advantage plans bundle Part D coverage into the plan. The Part D IRMAA surcharge is still assessed, but it is less visible because it is embedded in the total premium. When you switch to Original Medicare with a standalone Part D plan, the Part D IRMAA appears as a separate line item on your premium bill.

For a single filer with a 2024 MAGI of $212,000, the Part D IRMAA surcharge is $81.00 per month in 2026.⁸ This adds $972 per year to healthcare costs that may not have been visible under a Medicare Advantage plan.

Before switching during OEP, check your most recent tax return to estimate your IRMAA bracket. If you are near a threshold, consider whether a one-time event like a Roth conversion or capital gain realization pushed your income higher. You can file an IRMAA appeal using Form SSA-44 if your income has decreased due to a life-changing event such as retirement or divorce.

Three Critical Deadlines to Mark on Your Calendar Before March 31

1. January 31 — First-month review deadline. By the end of January, you should have received your first Explanation of Benefits from your Medicare Advantage plan for the new year. Review it for unexpected denials, out-of-network charges, or higher-than-expected copays. If something is wrong, you have two months to switch.

2. March 15 — Mid-month switch cutoff. If you want your new coverage to begin April 1, you must complete your enrollment by March 15. Enrollments processed after March 15 take effect May 1. Given that OEP ends March 31, any enrollment after March 15 leaves only 16 days to complete the process.

3. March 31 — OEP deadline. No exceptions. After this date, you cannot make any changes until the Fall AEP opens October 15. If you miss this deadline and your current plan is not working, you are stuck with it for the remainder of the year.

Set calendar reminders for each of these dates. The consequences of missing the March 31 deadline are significant — you lose the ability to change plans for nine months.

Your Next Step

Review your current Medicare Advantage plan's Explanation of Benefits for January and February. Compare the actual costs you have incurred against the plan's Summary of Benefits document. If you find unexpected copays, denied claims, or out-of-network charges, use the Medicare Plan Finder tool to compare available plans in your area. Complete any switch by March 15 to ensure April 1 coverage effective date. If you are considering returning to Original Medicare, contact your State Health Insurance Assistance Program (SHIP) for free, unbiased counseling before making the change.