Mastering the CMS MMR File: Your Complete Guide to Medicare Advantage Payments, Risk Adjustment, and Financial Accuracy

The definitive resource for coders, compliance analysts, and MA operations teams

Introduction: Why the MMR Is Your Monthly Financial Playbook

If you're working in Medicare Advantage or Part D, the Monthly Membership Report (MMR) Detail File isn't just another CMS data dump—it's your financial DNA from CMS. Every line item reveals what was paid, why it changed, and what risk model was applied to your beneficiaries.

For Medicare Advantage Organizations (MAOs), this file represents one of the most critical—yet often underutilized—tools for revenue validation, compliance tracking, and risk adjustment accuracy. Think of it as the pulse of your plan's payments, containing the entire reasoning behind every dollar CMS sends your way.

What Is the MMR Detail File?

The Monthly Membership Report (MMR) Detail File is the official CMS data file used to track monthly capitation payments, adjustments, and risk scores for Medicare Advantage and Part D beneficiaries. Each row in the file reflects a payment event—whether it's an original capitation, a retroactive adjustment, or a cleanup record—associated with a beneficiary enrolled in your MA plan.

Key Technical Specifications:

  • Format: Fixed-width, 495-character record layout

  • Frequency: Monthly delivery to MA plans

  • Structure: Every variable has a specific character position

  • Usage: MA Plans, Part D Plans, Compliance Audits, RAS Submissions

Comprehensive Breakdown: The 91 Fields Inside Your MMR

The MMR is organized into logical sections that paint a complete picture of your beneficiary payments and risk adjustments:

Beneficiary Demographics & Contract Information

  • Contract Number (positions 1–5): Your CMS-assigned plan contract (e.g., H1234)

  • Plan Benefit Package (PBP) ID (6–8): Specific product under the contract

  • Segment ID (9–10): Identifies the plan segment if the plan is regional

  • Beneficiary ID (20–31): May include either HICN or the new Medicare Beneficiary Identifier (MBI)

  • Member Details: Name, Gender, DOB, State & County Code

  • Status Indicators: Hospice, ESRD, Medicaid, Institutional, Dual-Status

  • OREC (Original Reason for Entitlement Code): Distinguishes beneficiaries by entitlement type—age-in, disability, or ESRD

Risk Adjustment & Payment Logic

  • RAF A/B (Fields 24–25): Core risk adjustment factors

  • Part C Risk Adjustment Factors (positions 72–85): Values for community, institutional, ESRD, or new enrollee categories

  • Risk Adjustment Factor Type Code (Field 46): Specifies which risk model was applied

  • RAAG – Risk Adjustment Age Group (Field 40): Age-based risk categorization

  • Default Risk Factor Code (Field 71/87): Applied when CMS uses default RAF due to insufficient risk data

Payment Components & Financial Details

  • Monthly Capitated Payments (positions 96–123): Separate values for Part A and B

  • Monthly Part A, B, D amounts: Base payment calculations

  • Rebate fields (Part C/D): Plan-specific rebate amounts

  • Low-Income & Medicaid Add-On Fields (Fields 20, 66, 67, 68): Additional subsidies and wraparound payments

  • MTM Add-on, LIS Premium Subsidy, Reinsurance, Direct Subsidy: Supplemental payment components

County-Level Payment Rates (Fields 88–90)

CMS uses county-level benchmarks to calculate payments:

  • Field 88 – Part A Rate: Monthly Part A state/county payment or adjustment rate

  • Field 89 – Part B Rate: Monthly Part B state/county payment or adjustment rate

  • Field 90 – Part D Rate: Monthly Part D payment or adjustment rate

These fields show the base amounts before risk adjustments—crucial for reconciling rate changes or benchmarking CMS payments.

Adjustments & Reconciliation Tracking

  • ARC – Adjustment Reason Code (Field 28): The "receipt" behind every payment change

  • Cleanup ID (Field 91/positions 486–495): Tracks systemic CMS cleanup events or batch adjustments

  • Transaction Type Code: Indicates if the row is original or a correction

  • Start and End Dates (Fields 29–30): Payment period coverage

Deep Dive: ARC Codes - Your Audit Trail for Payment Changes

Adjustment Reason Codes (ARC) are found in multiple CMS files and represent the "why" behind every payment modification CMS makes.

Where You'll Find ARC Codes:

  • MMR Detail Report (Field 28)

  • MMR Summary Report (Field 4)

  • PPR/IPPR Capitated Payment Files (Field 4)

Complete ARC Code Categories

Range Reason 00 Standard prospective payments 01–22 Retroactive enrollment & eligibility 23–27 Risk adjustment changes 28–37 Premium/rebate adjustments 38–46 Segment ID or eligibility corrections 50–66 Merge, incarceration, lawful status 90–94 System-driven CMS cleanup events

Critical ARC Codes to Monitor

  • 01 – Death Notification: Retroactive termination adjustments

  • 07 – Retroactive Hospice: Member moved to hospice care

  • 10 – Retroactive Medicaid: Dual eligibility status change

  • 25 – Part C RAF Reconciliation: Risk score adjustments

  • 36 – Part D Rate Change: Premium or rate modifications

  • 44 – Correction of Previously Failed Payment: System error corrections

  • 65 – Incarceration Status Confirmed: Eligibility suspension

  • 94 – Cleanup-Related Adjustment: Batch system corrections

Pro Tip: If payment amounts shift unexpectedly, check ARC first. It's your complete audit trail and the key to understanding revenue fluctuations.

Critical Focus: Part D Default Risk Factor Evolution

Field 87 (Default Risk Factor Code) identifies default RAF logic when a beneficiary has insufficient Medicare entitlement or RAS data—and it's undergoing significant changes.

Historical Logic (January 2011–December 2024):

  • 0 = Not ESRD, Not Low Income, Not Originally Disabled

  • 5 = ESRD, Low Income, Not Originally Disabled

  • 7 = ESRD, Low Income, Originally Disabled

  • (Additional combinations for Low Income, ESRD, and disability flags)

NEW: Starting January 2025:

  • A = Not ESRD, Not Low Income, Not Originally Disabled, MAPD

  • F = ESRD, Low Income, Originally Disabled, MAPD

  • P = ESRD, Low Income, Originally Disabled, PDP

  • N = Not ESRD, Low Income, Not Originally Disabled, PDP

  • (Full classification system includes more combinations)

This evolution helps CMS calculate RAF more precisely when claims data is missing or eligibility is partial, particularly distinguishing between MAPD and PDP enrollees.

Strategic Applications: Making Your MMR File Actionable

Understanding the MMR file layout gives MA plans significant operational advantages across multiple departments:

1. Revenue Validation & Financial Reconciliation

  • Compare CMS payments with internal projections based on RAF, demographics, and enrollment history

  • Validate that risk scores align with documented conditions and HCC mappings

  • Track month-over-month payment changes and identify revenue trends

2. Identify Revenue Leakage Opportunities

Monitor for these red flags:

  • Records flagged with default risk factors: Potential missed coding opportunities

  • ARC codes pointing to deletions: Reductions in past payments requiring investigation

  • Retroactive termination adjustments: Revenue clawbacks due to eligibility changes

  • Incorrect segment ID assignments: Payment miscategorizations

3. Compliance & Audit Readiness

  • CMS, OIG, and internal compliance teams audit based on these payment events

  • The MMR provides the complete transactional trail needed to reconcile discrepancies

  • Track Cleanup IDs for large-scale CMS retroactions (overpayment recovery or OIG audits)

  • Document the rationale behind every risk score and payment adjustment

4. Risk Adjustment Optimization

  • Link risk scores and payments to actual diagnoses documented in claims or EMRs

  • Uncover coding gaps or documentation errors impacting revenue

  • Monitor RAF changes with Fields 24–26, 46, and 87 to identify diagnosis, plan status, or demographic impacts

  • Cross-reference date fields (29–30) to ensure payment periods match ARC context

V28 Model Impact: New Challenges for MMR Analysis

CMS's V28 model has eliminated 2,200+ ICD-10 codes from HCC mapping, creating new MMR monitoring requirements:

What to Expect:

  • More RAF recalibrations as codes move from vague to specific (E11.69 → E11.22 or E11.319)

  • Increased frequency of ARC 25, 26, 37, and 41 as RAF updates ripple through the system

  • Greater importance of documentation accuracy and coding specificity

  • More default risk factor applications during transition periods

This makes your MMR analysis more critical than ever for identifying coding opportunities and revenue optimization.

Expert Tips for Analysts & Coders

Monthly Monitoring Best Practices:

  1. Always Monitor ARC Codes (Field 28): They provide the "why" for retroactive payments, flags, and cleanups

  2. Track Cleanup IDs (Field 91): Identify systemic adjustments or RAS audit overpayments

  3. Monitor RAF Changes: Use Fields 24–26, 46, 87 to spot diagnosis, plan status, or demographic impacts

  4. Validate Date Ranges: Ensure payment start/end dates (Fields 29–30) match ARC context

  5. Cross-Reference Member Data: Match MBI/HICN and segment IDs with internal systems

Technical Implementation:

  • Use ETL scripts or SQL loaders to parse the fixed-width format into readable tables

  • Export MMR data into Excel or Power BI for dashboard creation and trend analysis

  • Create automated alerts for unusual ARC patterns or significant RAF changes

  • Build reconciliation reports linking MMR data to internal risk adjustment and enrollment systems

Advanced Analytics Applications:

  • ARC trend analysis by plan segment or time period

  • RAF monitoring dashboards tracking risk score evolution

  • Revenue leakage identification through payment variance analysis

  • Compliance reporting for audit preparation and regulatory submissions

Conclusion: Know Your MMR, Own Your Financial Accuracy

The MMR Detail File isn't just another CMS data file—it's the financial blueprint that drives how much your plan gets paid, when, and why. Whether you're in Finance, Risk Adjustment, Compliance, or Operations, mastering this file structure is essential for maintaining accuracy, avoiding revenue leakage, and staying audit-ready.

By understanding its 91 fields, tracking ARC and RAF changes, and leveraging the diagnostic logic tied to payment adjustments, you'll boost your team's confidence, compliance, and financial performance. In the evolving landscape of Medicare Advantage—particularly with V28 model changes—your MMR expertise becomes a competitive advantage that directly impacts your bottom line.

The MMR is your monthly playbook for payment accuracy. Make it count.

Bonus Resources

  • CMS MARx User Guide: Official CMS documentation for MMR file specifications

  • AHIMA Risk Adjustment Coding & Reporting: Professional coding guidance and best practices

  • CMS Medicare Advantage Rate Announcements: Annual updates on payment methodology and risk adjustment changes