Appealing a Part B Claim Denial: Step-by-Step

If Medicare denies a Part B claim, you do not have to stop at the first “no.” Under Original Medicare, Part B claim denials can be appealed through a formal process that starts with your Medicare Summary Notice (MSN) and can move through as many as five levels if needed.

What this post is about

This guide is for people with Original Medicare Part B, not Medicare Advantage or Part D drug plans. In Original Medicare, the first appeal level is called a redetermination, and the instructions for starting it are tied to your MSN.

First, know what a denial really means

A Medicare Summary Notice is not a bill. It is a notice that shows what providers billed to Medicare, what Medicare paid, and the maximum amount you may owe. If an item or service is denied, the MSN tells you where to look next and says the last page includes step-by-step appeal directions.

Before you appeal, it is smart to compare the MSN with your bills, receipts, and records of care. Medicare specifically recommends checking whether you actually received the listed services and contacting the provider’s office if something looks wrong, since the office may be able to correct and resubmit the claim.

Step 1: Find the denied item on your MSN

Start with the MSN that shows the denied Part B service or payment decision. Medicare says to begin your appeal by looking at your MSN and to file by the deadline listed there. If you miss the deadline, you may still be able to appeal if you can show good cause for missing it, such as an illness, disability, or accident that delayed you.

Step 2: Gather the information that supports your case

Medicare says your appeal will usually be stronger if you ask your provider or supplier for information that supports it. Helpful documents can include doctor notes, medical records, a letter explaining medical necessity, billing corrections, or any paperwork that explains why the service should have been covered.

Step 3: File your first appeal, called a redetermination

For Original Medicare Part B, the first appeal is a redetermination by a Medicare Administrative Contractor (MAC). You generally have 120 days from the date you receive the initial claim determination to request it. CMS says the initial determination is communicated on the beneficiary’s MSN.

You can file that first appeal in either of two main ways:

Option 1: Fill out the Redetermination Request Form (CMS-20027). Medicare and CMS both identify CMS-20027 as the standard form for requesting a first-level appeal.

Option 2: Follow the instructions on your MSN. Medicare says you can circle the item or service you want to appeal on a copy of the MSN, explain in writing why you disagree, include your identifying information, add any supporting information, and mail it to the Medicare claims office address listed in Step 7 on the last page of the MSN.

Step 4: Make sure your appeal includes the right details

Medicare says your written redetermination request should include your name, address, Medicare number, the specific items or services and dates you are appealing, why you think they should be covered, and any supporting documentation. If someone is representing you, include an Appointment of Representative form or another written document with the required elements.

Step 5: Watch for the decision

Medicare says you will generally get a decision from the MAC within 60 days after it receives your appeal. If the MAC agrees with you, the covered item or service will show up on a later MSN. If the MAC still denies coverage, you should receive a written decision called a Medicare Redetermination Notice (MRN).

Step 6: If needed, ask for the second appeal

If you disagree with the first appeal decision, the next level is a reconsideration by a Qualified Independent Contractor (QIC). Medicare says you have 180 days after you get the MAC’s decision letter or MSN to request this second-level appeal. CMS also notes that the redetermination decision is presumed received 5 days after the date on the notice, unless there is evidence otherwise.

You can request reconsideration by using Medicare Reconsideration Request Form (CMS-20033) or by sending a written request with the required information to the QIC listed on your redetermination notice. CMS says there is no minimum dollar amount required for this second-level appeal.

Step 7: Keep going only if it makes sense

If you still disagree after reconsideration, Original Medicare appeals can continue to higher levels: an Administrative Law Judge hearing through OMHA, review by the Medicare Appeals Council, and then judicial review in federal district court. Medicare says there are five total levels, though the higher levels may have extra requirements, including minimum dollar thresholds at some stages. For 2026, Medicare lists a $200 minimum amount for level 3 and $1,960 for level 5.

Common reasons Part B appeals succeed

Many Part B denials come down to paperwork, coding, documentation, or whether Medicare had enough information to see why the service was medically necessary. That is why Medicare encourages you to get supporting information from your provider and include any documents that help explain why the service should be covered.

Common mistakes to avoid

Missing the deadline

The first appeal must be filed by the date on your MSN, and Medicare says late appeals may only move forward if you show good cause.

Appealing without evidence

Medicare and CMS both indicate that supporting information can strengthen your case, especially when the issue involves medical necessity or incomplete documentation.

Sending it to the wrong place

For a first-level Part B appeal, Medicare says to send it to the address listed on the last page of your MSN. For a second-level appeal, the request goes to the QIC listed on the redetermination notice.

Confusing Original Medicare with Medicare Advantage

This post covers Original Medicare Part B appeals. Medicare Advantage and Part D use different appeal paths.

A simple checklist before you mail your appeal

Before you send your first appeal, make sure you have:

• The MSN showing the denied Part B item or service
• The date or deadline from the MSN
• The exact service and date of service you are appealing
• A written explanation of why you disagree
• Supporting documents from your doctor or provider
• Your name, address, and Medicare number
• Representative paperwork, if someone is helping you formally appeal