Only 2% of denied Original Medicare claims get appealed. Here's how to be one of them.

This post is for people with Original Medicare (Parts A and B). If you have a Medicare Advantage plan, your appeal rules are different: see our Medicare Advantage page.

When Medicare denies a claim, most people do nothing. Some pay the bill. Some set the notice aside and forget it. The Centers for Medicare & Medicaid Services (CMS), the federal agency that runs Medicare, keeps count, and the numbers are striking.

Stat card: CMS, Original Medicare Claim Appeals Data, calendar year 2025

2% of denied Original Medicare claims were appealed to the first level. (Appeals by everyone who can file, including doctors, labs, and other providers.)

Initial denial rates: Part A 8%, Part B 10%.

First level of appeal, decided claims from all appellants, not counting dismissed appeals: Part B, 45% fully favorable and another 3% partially favorable. Part A, 39% fully and 4% partially favorable.

Second level, same basis: Part B, 24% fully favorable.

Here’s the catch: that 45% is not a “patient success rate.” It counts appeals from all appellants, including providers and suppliers, and CMS doesn’t break the results out by who filed. It also leaves out appeals that were dismissed (for example, filed late or missing information). So don’t read it as your odds. Read it this way: a first-level decision can go the other way, and very few people ever ask.

1. Find the denial on your Medicare Summary Notice (MSN)

Your Medicare Summary Notice (MSN) is the statement Original Medicare sends that lists services billed to Medicare. It’s not a bill. It’s also the document that starts your appeal.

On the pages that list your claims, look for these columns:

“Service Approved?” A “No” here is a denial.
“Maximum You May Be Billed.” This is the most you may owe the provider for that line. A big number next to a “No” is the line to look at.
“See Notes Below.” This points to a short message explaining why Medicare denied the service. In plain words, common reasons include:
Medicare doesn’t consider the service medically necessary for the diagnosis listed.
You had the test or service too recently (a frequency limit).
Information was missing or incorrect on the claim.
The service isn’t covered by Medicare at all.

The last page of the MSN tells you when and how to appeal, and gives the address to send your appeal.

Action step: Check your MSN against your bills. If a provider bills you for a service before the MSN arrives, wait for the MSN so you can compare before you pay.

2. Watch the 120-day clock

You have 120 days from the day you receive the MSN to ask for the first appeal, which Medicare calls a redetermination. Medicare assumes you received the MSN 5 days after the date printed on it. Your request counts as filed on the day the Medicare contractor receives it, not the day you mail it. So don’t count on extra days. Circle the deadline the day the MSN arrives, and mail early.

3. Check for an easy fix first

Some denials aren’t about whether you needed the care. They’re paperwork mistakes.

Wrong diagnosis on a lab order. Labs bill Medicare using the diagnosis your doctor wrote on the order. If the wrong one was used, Medicare may deny the test as not medically necessary. Ask the ordering doctor’s office to correct the order, then ask the lab to resubmit the claim. Medicare.gov suggests calling the provider’s office first to make sure it submitted the correct information. Simple errors can often be fixed through a correction process called a “reopening” instead of an appeal.
Frequency limits. Medicare covers some tests only so often. If yours was “too soon,” ask your doctor whether there was a medical reason for the timing. If there was, that reason belongs in your appeal.

Asking for a reopening does not pause the 120-day appeal clock. If a correction isn’t done well before the deadline, send the appeal anyway.

4. The $0 rule when there’s no valid ABN

An Advance Beneficiary Notice of Noncoverage (ABN) is a form a provider must give you before a service when it expects Medicare may deny it, for example as not medically necessary or too frequent. You sign it to show you knew and chose to go ahead.

If Medicare denies a service for one of those reasons and the provider did not give you a valid, signed ABN beforehand, you generally owe $0 for that denied service. That’s federal law (Section 1879 of the Social Security Act). An ABN signed after the fact, or one with the required blanks left empty, isn’t valid. (This rule doesn’t cover services Medicare never covers at all.)

Action step: If you’re billed for a denied service, ask the provider in writing for a copy of the ABN you signed. No ABN? Say so in your appeal and in writing to the provider. See your ABN rights. GougeStop, now part of Medterpret, has a no-ABN dispute letter for exactly this: GougeStop.

5. What goes in a redetermination request

Keep it simple. Send these to the Medicare contractor at the address on your MSN:

A copy of your MSN with the denied items circled.
A short letter (or the Redetermination Request Form, CMS-20027) with your name, address, and Medicare Number; the service and date of service; and one or two sentences on why it should be covered.
Supporting records, such as a short note from your doctor explaining why the service was needed, or the corrected order.
Form CMS-1696 (Appointment of Representative) if a family member is handling the appeal for you.

Keep copies of everything, and write down the date you mailed it.

6. If the answer is still no: Level 2

If the first appeal is denied, the decision letter explains the next step: a reconsideration by a Qualified Independent Contractor (QIC), an outside reviewer. You have 180 days from getting that decision to ask. Level 2 is a good time to add anything you didn’t send the first time, such as a stronger letter from your doctor.

A note from our founder

I’m David Rockaway, and I’m on Original Medicare in Texas. I once missed the 120-day window on a denied claim. That’s one of the reasons Medterpret calculates your deadline and reminds you before it passes.

What to do this week

[ ] Pull out your latest MSN (paper or in your Medicare.gov account).
[ ] Look for “No” under “Service Approved?” and check “Maximum You May Be Billed.”
[ ] Write the 120-day deadline on your calendar.
[ ] Call the provider: was the claim filed with the right information?
[ ] Billed for a denied service? Ask for a copy of the signed ABN.
[ ] Still wrong? Send the MSN copy, a short letter, and your doctor’s note to the address on the MSN.

Bottom line: In 2025, only 2% of denied Original Medicare claims were appealed. A first appeal has no filing fee, needs no lawyer, and starts with a document you already have. Read the MSN, mind the 120 days, and ask.

Got a denial or a confusing notice? Upload your MSN to Medterpret and see what it says, what it means, and what to do next, in plain English. Medterpret drafts your redetermination document, calculates your 120-day deadline, and reminds you; you decide what to send. Appeal a denial →

Founding members: $69 a year, locked in for as long as you stay a member. Open to the first 500 members or through December 31, 2026, whichever comes first. Reserve My Founding Rate (no card needed). Founding rate →

Medterpret is independent and not affiliated with or endorsed by Medicare, CMS, HHS, or any government agency. Educational information, not legal or medical advice.

More: Original Medicare · ABN rights

Sources

CMS, Original Medicare Claim Appeals Data – 2025 fact sheet (file “OrigMedicareFactSheet2025final.pdf,” May 2026), inside the “Appeals Fact Sheets” ZIP — cms.gov
CMS, “First Level of Appeal: Redetermination by a Medicare Contractor,” accessed Sept. 29, 2026 — cms.gov
Medicare.gov (CMS), “Appeals in Original Medicare,” accessed Sept. 29, 2026 — medicare.gov
Medicare.gov (CMS), “Medicare Summary Notice (MSN),” accessed Sept. 29, 2026 — medicare.gov
CMS, Medicare Appeals (CMS Product No. 11525), April 2026 — medicare.gov
42 CFR § 405.942, “Time frame for filing a request for a redetermination,” via Cornell Legal Information Institute — law.cornell.edu
42 CFR § 405.980, “Reopening of initial determinations, redeterminations, reconsiderations, decisions, and reviews,” via Cornell Legal Information Institute — law.cornell.edu
Social Security Act § 1879, 42 U.S.C. § 1395pp, “Limitation on liability where claims are disallowed,” via Cornell Legal Information Institute — law.cornell.edu
CMS, Medicare Claims Processing Manual, Pub. 100-04, Chapter 30, §50.8 (“Effective ABN Delivery”) — cms.gov
CMS, Form CMS-20027, “Medicare Redetermination Request Form – 1st Level of Appeal” — cms.gov
CMS, Form CMS-1696, “Appointment of Representative” — cms.gov