Short answer: a screening colonoscopy is free — $0 — if your provider accepts assignment and no polyp is found. But if your provider finds and removes a polyp or takes a tissue sample during that same screening, the visit becomes a diagnostic procedure. You then owe 15% coinsurance of the Medicare-approved amount, with the Part B deductible waived. This is the single biggest source of "surprise" colonoscopy bills — the procedure changes classification mid-visit, based on what the doctor finds, not on anything you chose.
Why a "Free" Screening Isn't Always Free
Medicare covers screening colonoscopies as prevention — looking for colorectal cancer before you have symptoms. If your provider accepts assignment and finds nothing that needs treatment, you pay nothing. But screening and treatment often happen in the same appointment: if the doctor sees a polyp, the standard of care is to remove it right then rather than schedule a second procedure. The moment that happens, Medicare's billing rules reclassify the service from "screening" to "diagnostic," because you're no longer just looking — you're treating something that was found.
What You Actually Pay
If a polyp or tissue is removed during a screening colonoscopy, you owe 15% of the Medicare-approved amount for the provider's services. The Part B deductible does not apply to this charge. If the procedure happens in a hospital outpatient department or ambulatory surgical center, you also pay the facility a 15% coinsurance.
That 15% rate isn't permanent — it's the middle step of a scheduled phase-down toward $0. Under Section 122 of the Consolidated Appropriations Act, the coinsurance for a screening test that becomes diagnostic due to polyp removal follows this schedule:
- 2022: 20% coinsurance.
- 2023–2026: 15% coinsurance (today's rate).
- 2027–2029: 10% coinsurance.
- 2030 and after: 0% coinsurance — the screening-turned-diagnostic charge goes away entirely.
How Often Screening Colonoscopies Are Covered
How often Medicare pays for a screening colonoscopy depends on your risk level:
- Once every 24 months if you're at high risk for colorectal cancer.
- Once every 120 months if you're not high risk — or every 48 months after a previous flexible sigmoidoscopy.
Staying within those windows is part of what keeps the procedure classified as a covered screening in the first place. See Understanding Your Costs for how Part B coinsurance and deductibles work more generally, and Medicare Part B for what else falls under medical insurance.
What to Ask Before the Procedure
You can't know in advance whether a polyp will be found, so you can't avoid this cost by planning around it. What you can do is ask your provider's office, before the appointment, how they bill if a polyp is removed during a screening — some practices can walk you through the coding in advance so the bill isn't a surprise. If you get a bill you don't understand, our common billing mistakes guide covers how to check a claim before you pay it.
Common Questions
Does Medicare cover colonoscopies for free?
A screening colonoscopy is free if your provider accepts assignment and no polyp is found. If a polyp is found and removed during that same screening, the visit becomes diagnostic and you owe coinsurance.
How much will I owe if a polyp is removed?
For 2023 through 2026, you owe 15% of the Medicare-approved amount, with no Part B deductible. That coinsurance is scheduled to drop to 10% for 2027 through 2029, then to 0% starting in 2030.
Does this happen with other free screenings too?
The screening-to-diagnostic switch is most visible with colonoscopies, but the same idea applies broadly: a preventive visit stops being free the moment it turns into treatment for something found during that visit. Ask your provider whether a specific step is still part of the screening or has become diagnostic care.