Medicare Denial vs. Adjustment: What's the Difference?

The Short Answer

• A denial means Medicare refused to pay for the service. You may be able to appeal.
• An adjustment means Medicare approved the claim but you owe a portion (like a deductible, coinsurance, or copay). This is standard cost-sharing.

The difference matters because it determines your next step. If it’s a denial, the question is whether Medicare should have paid at all. If it’s an adjustment, the question is whether your share was calculated correctly.

An adjustment is not a dead end. You cannot appeal the cost-sharing rates — that Part B coinsurance is 20%, or that there is an annual deductible at all, is set by law. But whether your deductible had already been met, and how the coinsurance was computed, are formal “initial determinations” under 42 CFR 405.924(b)(4) and (b)(5) — which means they carry the same appeal rights as an outright denial. What you cannot appeal is the rate-setting itself: the fee schedule Medicare pays from, and the cost-sharing amounts fixed by regulation for hospital outpatient services, are both matters of general policy that 42 CFR 405.926 puts outside the appeals process. How those rules were applied to your claim is a different thing, and it is reviewable.

Which deadline you have depends on which kind of Medicare you have. Under Original Medicare you file a redetermination within 120 days of receiving your Medicare Summary Notice. If you are in a Medicare Advantage plan, the notice is an Explanation of Benefits, the route is your plan rather than Medicare, and the window is shorter — 65 days from the date on the notice (Medicare.gov). Do not take the 120 days as yours unless you have Original Medicare.

The codes on a claim explain the adjustment. X12 group codes identify the liability category: PR means patient responsibility, CO contractual obligation, and OA other adjustment. The separate numeric Claim Adjustment Reason Code (CARC) explains why an amount was adjusted. Read both codes and the claim’s paid and denied amounts; a group prefix alone does not tell you whether the entire service was approved or denied.

How To Tell the Difference

It’s a denial if your notice says:

• “Claim denied” or “not approved”
• “This service is not covered”
• “Not medically necessary”
• “The time limit for filing has expired”
• A specific reason Medicare refused to pay

It’s an adjustment if your notice shows:

• “Deductible amount” or “applied to your deductible”
• “Coinsurance” — your percentage share of the cost
• “Copay” or “copayment”
• Medicare paid a portion and you owe the rest

What To Do

If it’s a denial: Find your specific denial reason in our Denial Guide to understand what happened and whether to appeal.

If it’s an adjustment: Verify the amount is correct. Check that the deductible, coinsurance, or copay matches your plan’s terms — in particular, check whether you had already met your Part B deductible for the year, because that is the single most common thing to go wrong. If you have supplemental insurance (Medigap, Medicaid, employer coverage), it may cover some or all of your share. See our Patient Responsibility section for more details. If the arithmetic still looks wrong after that, you can appeal it — a miscounted deductible or a miscomputed coinsurance amount is an appealable initial determination, on the same deadline as a denial: 120 days from receipt of your Medicare Summary Notice under Original Medicare, or 65 days from the date on the notice if you are in a Medicare Advantage plan.

If the bill doesn’t match your Medicare statement: Your provider may have sent you a bill before Medicare finished processing the claim. This is a timing issue. Providers must submit your claim to Medicare rather than billing you for it directly, and a provider who accepts assignment has additionally agreed to take the Medicare-approved amount as payment in full — so the provider’s bill should match what your Medicare Summary Notice (Original Medicare) or Explanation of Benefits (Medicare Advantage) shows you owe. Don’t pay the bill yet — wait for the MSN or EOB, compare the amounts, and call the provider’s billing office if they don’t match. This usually resolves in a single phone call. See our guide on Medigap crossover failures if your supplement didn’t pick up the remaining balance.

If you’re still not sure: Call 1-800-MEDICARE (1-800-633-4227) or contact your State Health Insurance Assistance Program (SHIP) for free help.

Sources

• Medicare.gov: Medicare Summary Notice (MSN) — what the MSN is, when it arrives, how it’s organized, and what a denied vs adjusted claim looks like on it.
• Medicare.gov: Checking the status of a claim — how to look up a Part A or Part B claim before the MSN arrives.
• Medicare.gov: Filing an appeal — what to do when the line item is a denial rather than an adjustment.
• 42 CFR 405.924 — Actions that are initial determinations — lists “whether the deductible is met” (b)(4) and “the computation of the coinsurance amount” (b)(5) among the determinations that carry appeal rights, which is why a disputed adjustment is not automatically the end of the road.
• X12: Claim Adjustment Group Codes — official definitions for the CO, PR, and OA prefixes. X12: Claim Adjustment Reason Codes (CARCs) — official definitions for the numeric reasons.

Frequently Asked Questions