Original Medicare covers eligible services for pre-existing conditions under the same benefit rules used for other health conditions. Medicare Advantage plans also cannot deny enrollment or Medicare-covered care because of a pre-existing condition. Coverage still depends on whether a service is medically necessary and included in Medicare benefits.
Original Medicare and Medicare Advantage
Part A and Part B do not impose a general exclusion period for a health problem that existed before Medicare coverage began. Normal deductibles, copayments, coinsurance, and coverage limits apply. Part D plans cover formulary drugs subject to plan rules and cannot refuse membership based on health status.
Medicare Advantage plans must cover almost all medically necessary services that Original Medicare covers. A plan may use provider networks, referrals, or prior authorization. These utilization rules are not pre-existing condition exclusions, but they can affect how care is obtained.
Medigap has different rules
Federal law provides a six-month Medigap Open Enrollment Period beginning the first month a person is both age 65 or older and enrolled in Part B. During this period, an insurer cannot deny an available Medigap policy or charge more because of health problems.
A Medigap insurer may impose a waiting period of up to six months for out-of-pocket costs related to a condition diagnosed or treated during the six months before the policy begins. Prior creditable coverage can shorten or eliminate that waiting period. Original Medicare continues to cover its share of eligible services during any Medigap waiting period.
After Medigap Open Enrollment, an insurer may use medical underwriting unless the applicant has a federal or state guaranteed-issue right. Availability and state protections vary. A Medigap policy already in force is generally guaranteed renewable as long as premiums are paid and application information was accurate.
What to do next
- Record the Part B effective date and the end of the Medigap Open Enrollment Period.
- Keep proof of prior health coverage when applying for Medigap.
- Ask an insurer in writing about underwriting and any waiting period before replacing coverage.
- Review Medicare’s Medigap enrollment rules and Medigap basics.
Sources
Coverage and costs can change each calendar year. Check current Medicare rules and current plan documents before receiving care. A provider’s estimate is not a Medicare coverage decision. Final payment depends on the claim and the applicable coverage requirements.
Last reviewed: August 2026. Medicare rules and plan benefits can change.