Every January, Medicare Advantage enrollees across the country discover that the plan they picked during October's Annual Enrollment Period does not quite work as expected. A primary care physician retired and left the network. A critical drug moved to a higher formulary tier, doubling the monthly copay. A specialist requires prior authorization that the new plan's process makes burdensome. Congress created the Medicare Advantage Open Enrollment Period precisely for these situations: a 90-day correction window from January 1 through March 31, 2027. During this period, any Medicare Advantage enrollee can make one plan change: switch to a different Medicare Advantage plan in their area, or drop Medicare Advantage entirely and return to Original Medicare (Parts A and B), adding a standalone Part D prescription drug plan. The OEP applies only to people already enrolled in a Medicare Advantage plan; it is not available to those on Original Medicare who want to switch into a Medicare Advantage plan for the first time.
Coverage under the 2027 OEP depends on exactly what you can and cannot change, how changes affect your coverage start date, the critical Medigap underwriting trap when returning to Original Medicare, and how to compare plans using the medicare.gov Plan Finder. The 2026 Part B standard premium is $202.90 per month. Medicare Advantage plan premiums for 2027 are set based on what you enrolled in during the 2026 AEP or switched to during the 2027 OEP. For those approaching 65 for the first time, the OEP is separate from the 7-month Initial Enrollment Period covered on our Medicare eligibility page. For the October switch window, see our Medicare Annual Enrollment Period page.
6 Steps to Get Coverage
Common Mistakes That Cost People Thousands
The costliest errors Medicare Advantage enrollees make during the January to March OEP:
- Disenrolling from Medicare Advantage without first securing a Medigap quote. In most states, Medigap insurers can use medical underwriting outside of guaranteed-issue windows. Switching to Original Medicare and then discovering you cannot get Medigap at any price leaves you with Original Medicare's unlimited 20 percent coinsurance exposure.
- Assuming the OEP lets you switch from Original Medicare into Medicare Advantage. The OEP is for current Medicare Advantage enrollees only. Original Medicare beneficiaries who want to join Medicare Advantage must wait for the Annual Enrollment Period (October 15 to December 7) or qualify for a Special Enrollment Period.
- Missing the Part D continuity gap. Returning to Original Medicare during the OEP without simultaneously enrolling in a Part D plan leaves a coverage gap. Any gap of 63 consecutive days or more without creditable drug coverage triggers a permanent Part D late enrollment penalty.
- Choosing a plan based on premium alone and ignoring drug formulary tiers. A Medicare Advantage plan with a $0 premium can cost $2,000 or more per year than a plan with a $50 monthly premium if your medications land on higher cost-sharing tiers. The medicare.gov Plan Finder drug-cost calculator reveals total annual cost; use it.
- Not checking whether low-income programs apply. Medicare Savings Programs (QMB, SLMB, QI) can eliminate your Part B premium entirely. Extra Help can reduce Part D copays to single digits. Neither program requires you to leave Medicare Advantage, and both are available year-round through your state Medicaid agency; most eligible beneficiaries never apply.
What the Medicare OEP Allows and What It Does Not Allow
Medicare Advantage Open Enrollment Period rules are narrower than the October Annual Enrollment Period. During the January 1 to March 31 OEP, current Medicare Advantage enrollees may make exactly one plan change. Permitted actions: switch from one Medicare Advantage plan to another Medicare Advantage plan in your area, or disenroll from Medicare Advantage and return to Original Medicare (Parts A and B) while simultaneously enrolling in a standalone Part D prescription drug plan. Prohibited actions: switching from Original Medicare into a Medicare Advantage plan (this requires AEP or a qualifying Special Enrollment Period), buying or changing a Medigap supplemental policy through the OEP itself (Medigap has its own enrollment rules), or making more than one plan change during the OEP window.
Coverage effective dates during the OEP depend on when you submit your enrollment. Unlike the Annual Enrollment Period (where all changes take effect January 1), OEP changes take effect the first day of the month following your enrollment request. Submit in January and coverage starts February 1. Submit in March and coverage starts April 1. This means earlier action in the OEP window gives more months of corrected coverage before year-end. CMS confirmed these rules under 42 CFR 422.62(a)(3), which governs Medicare Advantage enrollment periods.
The Medigap Underwriting Trap: What to Check Before Returning to Original Medicare
Medigap supplemental policies fill the 20 percent coinsurance gap in Original Medicare; without one, a $100,000 hospitalization leaves an uncapped $20,000-plus obligation on the enrollee. The critical issue when returning to Original Medicare through the OEP: federal law does not grant guaranteed-issue rights to purchase Medigap simply because you disenrolled from Medicare Advantage. In most states, Medigap insurers can apply full medical underwriting, meaning they review your health history, deny coverage, or charge significantly elevated premiums. Guaranteed-issue rights for Medigap apply in a narrower set of situations: within 12 months of first enrolling in Medicare Advantage (the trial-right period), if your plan is leaving the service area or losing its contract, if you move out of the plan's coverage area, or if you qualify for certain HIPAA-protected special circumstances.
Massachusetts, Minnesota, and Wisconsin have state-specific Medigap rules that provide broader guaranteed-issue protections than federal standards. Connecticut provides a birthday rule allowing Medigap switching once per year on a guaranteed-issue basis. California, Nevada, Idaho, Oregon, Illinois, Missouri, Louisiana, and a growing list of other states have enacted birthday rules or anniversary rules. Before disenrolling from any Medicare Advantage plan during the OEP, call at least three Medigap insurers, disclose any pre-existing conditions, and get written quotes. If you receive a denial or a prohibitively expensive quote, consider whether staying in Medicare Advantage or switching to a different Medicare Advantage plan is the better path for your situation.
How to Compare Medicare Advantage Plans Using medicare.gov Plan Finder in 2027
Medicare.gov Plan Finder is the official CMS comparison tool and the most reliable source for 2027 plan data during the OEP. Start by entering your ZIP code and current medications. The tool asks for each drug's name, dosage, and frequency, then calculates your estimated annual drug cost across every plan available in your area. Pay attention to three numbers for each plan: the monthly premium, the annual drug cost estimate, and the annual maximum out-of-pocket limit. Adding these three numbers together gives a rough total-cost-of-coverage estimate. The 2026 federal ceiling on Medicare Advantage in-network maximum out-of-pocket costs is $9,250; plans may set lower limits, and some preferred-provider tiers have separate higher limits for out-of-network care.
Star Ratings provide a quality signal alongside the cost comparison. CMS assigns Medicare Advantage plans a 1-to-5 star rating based on measures including member complaints, access to care, managing chronic conditions, and member experience. Plans rated 4 stars or higher received a quality bonus in their CMS payment rate, which plans may pass through as lower premiums or added benefits. A 3-star plan with a $0 premium may cost significantly more in total annual care costs than a 4.5-star plan with a $30 monthly premium, once formulary tier differences and prior-authorization denial rates are factored in. Check Star Ratings for any plan you are considering switching to during the 2027 OEP at medicare.gov.
Low-Income Medicare Programs Available Year-Round: Extra Help and Medicare Savings Programs
Extra Help (also called the Low Income Subsidy, or LIS) is a federal program that reduces Part D drug costs for Medicare beneficiaries with limited income and resources. In 2026, Extra Help covers most or all of the Part D premium and limits copays to under $10.35 per drug. Eligibility: income under 150 percent FPL (roughly $23,940 for a single person, $32,460 for a couple in 2026 for 48 states and DC) and limited assets. Apply at ssa.gov/extrahelp or call 1-800-772-1213. Extra Help eligibility does not require switching plans during the OEP; it applies to your current coverage.
Medicare Savings Programs (MSPs) are state-administered programs funded through Medicaid that help pay Medicare costs for enrollees with lower incomes. Four tiers exist: QMB (Qualified Medicare Beneficiary) pays Part A and Part B premiums, deductibles, and copays; SLMB (Specified Low-Income Medicare Beneficiary) pays only the Part B premium; QI (Qualifying Individual) also pays the Part B premium at a higher income tier; and QDWI (Qualified Disabled and Working Individuals) covers Part A premiums for working disabled beneficiaries. Income limits vary by state, but the federal floor in 2026 is 100 percent FPL for QMB, 120 percent FPL for SLMB, 135 percent FPL for QI, and up to 200 percent FPL for QDWI. Apply through your state Medicaid agency; enrollment is year-round and independent of OEP or AEP timing.
Frequently Asked Questions
What are the 2027 Medicare OEP dates?
The Medicare Advantage Open Enrollment Period for 2027 runs from January 1 through March 31, 2027. This is a fixed annual window, the same dates every year. Any change made during this window takes effect the first day of the month after you enroll. Submit in January and your new coverage starts February 1; submit in March and it starts April 1. Call 1-800-MEDICARE or visit medicare.gov to enroll or compare plans.
Who can use the Medicare OEP?
The Medicare Advantage OEP is available only to people currently enrolled in a Medicare Advantage (Part C) plan. Original Medicare beneficiaries who want to switch to Medicare Advantage cannot use the OEP; they must wait for the Annual Enrollment Period (October 15 to December 7) or qualify for a Special Enrollment Period. If you enrolled in Medicare Advantage during the 2026 AEP and regret the choice, the 2027 OEP is your correction window.
What can I change during the Medicare Advantage OEP?
During the OEP you can make one of two changes: switch from your current Medicare Advantage plan to a different Medicare Advantage plan in your service area, or disenroll from Medicare Advantage entirely and return to Original Medicare (Parts A and B) while adding a standalone Part D drug plan. You cannot use the OEP to join Medicare Advantage from Original Medicare, buy a Medigap policy, or make more than one plan change.
When do OEP coverage changes take effect?
Unlike the Annual Enrollment Period (where all changes take effect January 1), Medicare OEP changes take effect the first of the month following your enrollment request. Submit a plan change in January and new coverage starts February 1. Submit in February and coverage starts March 1. Submit by March 31 and coverage starts April 1. This effective-date rule means earlier action gives you more months of corrected coverage before the 2027 Annual Enrollment Period.
What if I miss the March 31, 2027 OEP deadline?
Missing the March 31 OEP deadline means you are generally locked into your current Medicare Advantage plan until the next Annual Enrollment Period (October 15 to December 7, 2027). Exceptions include qualifying Special Enrollment Periods triggered by specific events: moving out of your plan's service area, losing other creditable coverage, moving into or out of a nursing facility, qualifying for Extra Help, or your plan losing its CMS contract. Call 1-800-MEDICARE to check whether a SEP applies to your situation.
Can I get Medigap after switching back to Original Medicare through the OEP?
Getting Medigap after returning to Original Medicare through the OEP is not guaranteed in most states. Federal law does not grant automatic guaranteed-issue Medigap rights to people who disenroll from Medicare Advantage through the OEP; unlike the 12-month trial right after first joining Medicare Advantage. In most states, Medigap insurers can apply medical underwriting and deny your application or charge significantly more. States with birthday rules (California, Connecticut, Oregon, Nevada, Idaho, Illinois, Missouri, Louisiana) provide an annual window. Always get Medigap quotes before disenrolling from Medicare Advantage.
What is the difference between the Medicare OEP and the AEP?
The Medicare Annual Enrollment Period (AEP) runs October 15 to December 7 and is open to ALL Medicare beneficiaries; you can switch from Original Medicare to Medicare Advantage, between MA plans, or back to Original Medicare, and all changes take effect January 1. The Medicare Advantage OEP runs January 1 to March 31 and is only for current Medicare Advantage enrollees; it lets you switch between MA plans or return to Original Medicare, with changes effective the first of the next month. The OEP is a correction window; the AEP is the primary annual choice window.
Do I need to do anything during the OEP if I am happy with my current plan?
No action is required if your current Medicare Advantage plan still covers your doctors, medications at acceptable tiers, and your preferred pharmacy. Your plan auto-continues. However, using the OEP window to run a quick medicare.gov Plan Finder comparison takes about 15 minutes and may reveal a plan with lower total annual costs; especially if your drug costs changed since you enrolled. Also check whether you qualify for Extra Help or a Medicare Savings Program, which are year-round and could reduce your costs without a plan switch.
