Medicare Says Coverage Wasn't Active on That Date

What This Means

Medicare denied this claim because their records show you were not enrolled in Medicare coverage on the date the service was provided. The denial codes here are defined by X12: CO-27 (“expenses incurred after coverage terminated”) means the service happened after your coverage ended, and CO-26 (“expenses incurred prior to coverage”) means it happened before your coverage started.

This is an eligibility issue, not a judgment about whether you needed the care.

Why This Happens

• Your Medicare coverage hadn’t started yet. There may have been a gap between when you applied and when your coverage began. Since 2023, when you sign up for Part B during your Initial Enrollment Period or General Enrollment Period, coverage starts the first day of the month after you enroll — so there’s still a small lag, but it’s no longer the multi-month wait that applied before the Consolidated Appropriations Act, 2021 enrollment changes took effect.
• Your coverage ended or lapsed. If you stopped paying premiums or were disenrolled from a Medicare Advantage plan, there may be a period where you had no active coverage.
• You switched plans and there was a gap. Moving from Original Medicare to Medicare Advantage (or vice versa) can sometimes create a brief window where one plan has ended but the other hasn’t started.
• Medicare’s records are incorrect. Enrollment data errors do happen. Your coverage may have been active, but Medicare’s system doesn’t reflect it.
• Retroactive enrollment hasn’t been processed yet. If you recently enrolled through a Special Enrollment Period with a retroactive start date — for example, the SEP for people who lost Medicaid coverage on or after January 1, 2023 — it may take time for the enrollment to appear in Medicare’s systems.

Should You Appeal?

What To Do Next

1. Check your enrollment dates. Call Medicare at 1-800-MEDICARE (1-800-633-4227) or log in to Medicare.gov to confirm when your coverage started and ended.
2. If you were enrolled on that date, gather proof (your Medicare card, enrollment letter, premium payment records) and file an appeal. The denial may be due to a data error that can be corrected.
3. If there was a coverage gap, ask about retroactive enrollment. Contact Social Security at 1-800-772-1213 to find out if you qualify for a Special Enrollment Period that could backdate your coverage.
4. Contact your provider’s billing office. Let them know about the denial. They may be able to hold the bill while you resolve the enrollment issue, or they may be able to help verify your coverage.
5. If you need help, contact your State Health Insurance Assistance Program (SHIP) for free counseling. SHIP counselors can help you understand your enrollment status and options.

Sources

• CMS: Original Medicare (Part A and B) Eligibility and Enrollment — when Part A and Part B coverage starts based on enrollment timing.
• CMS: Implementing Certain Provisions of the Consolidated Appropriations Act, 2021 (CMS-4199-F) — fact sheet — primary source for the 2023 Part B start-date changes referenced above.
• CMS: Temporary Special Enrollment Period (SEP) for Loss of Medicaid — FAQ (PDF) — six-month SEP, effective dates, and retroactive start-date options.
• Medicare.gov: Filing an Appeal — appeal process and deadlines for both Original Medicare and Medicare Advantage.
• SSA: Sign up for Medicare — how to enroll and verify your enrollment dates with Social Security.
• X12: Claim Adjustment Reason Codes — definitions of CO-26 and CO-27 used on the EOB/MSN.

Frequently Asked Questions