What is a Medicare Administrative Contractor (MAC)?

The regional contractor that processes Medicare claims, publishes LCDs, runs the provider portal, and handles first-level appeals for your jurisdiction.

The Advance Beneficiary Notice - signed before an expected non-covered service, it preserves the right to bill the patient. Without it the write-off belongs to the practice.

Medicare Billing Guide: MACs, 12-Month Filing & 5-Level Appeals

Q: How long do I have to appeal a Medicare denial?

120 days from the remittance for redetermination with your MAC, then 180 days to the QIC reconsideration, with three more levels above.

Quick Facts

Item	Rule
Timely filing	12 months from the date of service — statutory, the most generous major-payer window (rare documented exceptions exist)
Who processes claims	Medicare Administrative Contractors (MACs) by geographic jurisdiction — your MAC is your portal, your LCD source, and your first-level appeals reviewer
First appeal (redetermination)	120 days from the remittance, filed with your MAC
Patient share	Part B: annual deductible, then 20% coinsurance of the allowed amount — no out-of-pocket maximum in traditional Medicare
Enrollment	PECOS enrollment and revalidation on schedule — lapsed enrollment stops payment entirely regardless of claim quality

Medicare (Fee-for-Service) Timely Filing Limits

Medicare's 12-month limit is set in statute, not negotiated — which makes it both the most generous window among major payers and the least flexible. Exceptions are narrow and specifically defined. The windows below are the ones most commonly published in provider manuals — treat them as a starting point, not a substitute for your executed contract, which overrides everything here. TFL is the abbreviation you will see in most payer documentation.

Claim type	Product	Typical window
Initial claim	Part A / Part B	12 months from date of service — statutory
Redetermination	Level 1 appeal	120 days from the initial determination
Reconsideration (QIC)	Level 2 appeal	180 days from the redetermination
ALJ hearing	Level 3 appeal	60 days from the reconsideration

The clock people miss: the corrected-claim and appeal windows are separate from the initial filing window, and they are usually shorter. At most payers they run from the date of the remit, not the date of service — so a claim filed on day 5 and denied on day 80 has not reset anything. This is the most common way a claim filed on time still ends up written off.

Once you know your window, our timely filing calculator turns it into the actual deadline date and days remaining. For every other payer side by side, see the timely filing limits by payer table. If a claim has already denied for late filing, CO-29 is the code you will see.

Why Medicare fluency compounds: its fee schedule anchors commercial contracts, its NCCI edits drive everyone's bundling logic, and its coverage rules become the arguments that win Medicare Advantage appeals. Learn Medicare deeply and every other payer gets easier.

Coverage: NCDs, LCDs, and the ABN

Medicare coverage runs on published rules: National Coverage Determinations set nationwide policy, and each MAC's Local Coverage Determinations fill the gaps with diagnosis-level specificity — the LCD's covered-diagnosis list is exactly what automated medical-necessity denials (CO-50 patterns) check against. When a service will not meet coverage rules, the ABN (Advance Beneficiary Notice) signed before the service is what preserves the right to bill the patient; without it, the write-off is yours. The discipline: check the LCD before the claim, not after the denial, and build ABN workflows for the services your specialty knows are coverage-limited.

The Five-Level Appeal Ladder

Redetermination — your MAC, within 120 days of the remit; different reviewer than the original processor
Reconsideration — a Qualified Independent Contractor (QIC), within 180 days of the redetermination decision; the last stage for submitting new evidence freely, so front-load the record here
Administrative Law Judge hearing — for amounts meeting the yearly threshold; a genuine hearing where providers with organized documentation do well
Medicare Appeals Council, then federal court — rare territory for routine billing, but the ladder's existence disciplines every level below it

Most working denials die at levels one and two — and the fixable ones (missing documentation, LCD diagnosis mismatches, CO-16 data problems) are usually better handled as corrected claims or reopenings than formal appeals. Save the ladder for genuine coverage disagreements, and draft the letters in minutes with the appeal letter generator.

The Recurring Medicare Realities

Sequestration: the ~2% federal payment reduction on every remit — expected, unappealable, never patient-billable; full treatment in our CO-253 guide
MSP (Medicare Secondary Payer): working aged, ESRD coordination periods, liability situations — billing Medicare primary when it is secondary generates the CO-22 family and recoupments; the MSP questionnaire at intake is the prevention
Crossover claims: Medicare forwards to Medigap plans automatically when enrollment files are right — secondary AR problems usually trace to crossover setup, not the supplement
Annual resets: fee schedule, deductible, and therapy thresholds move every January — calendar the update the way you calendar taxes
Medicare Advantage is a different world: MA plans follow their own contracts, auth lists, and appeal tracks — our Humana guide covers the MA operating mode in depth

For Patients With Medicare

Traditional Medicare's paper trail is the MSN (Medicare Summary Notice), arriving quarterly — read it like an EOB (our guide applies) and check that bills match its patient-responsibility figures. Appeals start right on the MSN with 120 days to file. Two structural facts worth knowing: traditional Medicare has no out-of-pocket maximum (which is what Medigap supplements exist to fix), and providers who "accept assignment" cannot bill you beyond the Medicare-approved amounts. For confusing bills, the universal toolkit applies — the dispute playbook and cost-sharing explainer both speak Medicare.

Why 12 Months Still Gets Missed

A year sounds unmissable — and yet CO-29 denials on Medicare claims happen constantly. The mechanism is always indirect: a claim bounces for enrollment or MSP reasons, waits months for the fix, and quietly crosses the line; or a claim sat with the wrong primary payer through a coordination-of-benefits dispute and arrived at Medicare thirteen months old. The defense is the same acceptance-report discipline every payer demands, plus one Medicare-specific move: when the delay was caused by retroactive entitlement or another qualifying circumstance, the filing-limit exceptions exist — narrow, documented, but real — and a well-evidenced exception request beats writing off a five-figure surgical claim.

Medicare Appeals: The Five Levels

Medicare fee-for-service has a formal five-level appeal structure defined in regulation, with fixed deadlines at each stage and a dollar threshold before the higher levels are available. Unlike commercial appeals, none of this is negotiable — the levels and windows are the same for every provider.

Level	Decided by	Deadline to file
1. Redetermination	The MAC	120 days from the initial determination
2. Reconsideration	Qualified Independent Contractor	180 days from the redetermination
3. ALJ hearing	Administrative Law Judge	60 days — minimum amount in controversy applies
4. Medicare Appeals Council	Departmental Appeals Board	60 days
5. Federal district court	Federal court	60 days — higher amount threshold applies

Level 1 is where almost everything is won or lost. The redetermination is your best opportunity to submit the documentation that supports the claim, and it is the cheapest stage to fight at. Appeals that reach an ALJ hearing take a long time and the amount in controversy has to justify it — which for most single professional claims, it will not.

Read the reason code before choosing a route. A coding error usually needs a corrected claim, not an appeal — appeals are for decisions you disagree with, corrections are for claims you got wrong. Filing the wrong one wastes the window.

Date the clock from the remit, not the service. Nearly every appeal window runs from the date of the remittance advice. Our appeal deadline calculator converts that into the actual date.

Attach the evidence the reason code asks for. Medical necessity denials need the clinical note and the coverage criteria; bundling denials need the operative report showing the services were distinct; eligibility denials need proof of coverage on the date of service.

Keep proof of submission. A dated clearinghouse acceptance report or a certified-mail receipt is what wins a "we never received it" dispute later. Our appeal letter generator handles the letter itself.

Medicaid works differently from every other payer here — see our Medicaid billing guide for why each state is effectively a separate payer, how managed care changes the rules, and why balance billing a Medicaid patient is generally prohibited.

Frequently Asked Questions

What is the timely filing limit for Medicare?

12 months from the date of service, set by statute - the most generous major-payer window. Exceptions are rare and narrowly defined (retroactive entitlement, administrative error).

What is a MAC?

A Medicare Administrative Contractor - the regional company that processes claims, publishes LCDs, runs the portal, and handles first-level appeals for your jurisdiction.

How long do I have to appeal a Medicare denial?

120 days from the remittance for the first level (redetermination with your MAC), then 180 days to the QIC reconsideration - with three more levels above for genuine disputes.

What is an ABN and when do I need one?

The Advance Beneficiary Notice - signed before a service Medicare is expected not to cover, it preserves the right to bill the patient. Without it, the non-covered write-off belongs to the practice.

How many levels of appeal does Medicare have?

Five. Redetermination by the MAC within 120 days of the initial determination, reconsideration by a Qualified Independent Contractor within 180 days, an Administrative Law Judge hearing within 60 days, the Medicare Appeals Council within 60 days, and finally federal district court. Minimum amount-in-controversy thresholds apply from the ALJ level onward.

Medicare Billing Guide: MACs, the 12-Month Clock & Five-Level Appeals