For Medicare Advantage Organizations (MAOs), the Monthly Membership Report (MMR) Detail File is one of the most critical — yet often underutilized — tools for revenue validation, compliance tracking, and risk adjustment accuracy. Let’s break down what this file contains, why it matters, and how to use it strategically.

📌 What Is the MMR Detail File?

The MMR Detail File is a monthly beneficiary-level transaction file sent by CMS to Medicare Advantage plans. 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 the MA plan.

The file is formatted as a fixed-width layout, meaning every variable has a specific position (e.g., characters 1–5 for contract ID), and spans over 400+ bytes per row. These rows are packed with data that, when decoded, reveal CMS’s entire reasoning behind payments made to your plan.

🧠 Key Data Elements in the MMR File

The file contains a wide range of information, but here are the most impactful data points:

🆔 Beneficiary and 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 the Health Insurance Claim Number (HICN) or the new Medicare Beneficiary Identifier (MBI).

🏥 Enrollment & Demographic Details

Gender Code, Date of Birth, and State/County Codes help match internal eligibility records and validate member metadata.

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

💰 Payment Breakdown

Monthly Capitated Payments (positions 96–123): Includes separate values for Part A and B.

Part C Risk Adjustment Factors (positions 72–85): These values determine the risk-adjusted revenue — community, institutional, ESRD, or new enrollee.

Default Risk Factor Code (71): Indicates when CMS applied a default RAF due to missing diagnosis or demographic data.

⚠️ Adjustment & Reconciliation Fields

Adjustment Reason Code (ARC) (90–91): Indicates why the payment record exists — retroactive enrollment, contract change, or data cleanup.

Cleanup ID (486–495): Used for batch corrections, typically flagged with an ID for tracking (e.g., SNOW tickets).

Transaction Type Code: Tells you if the row is original or a correction.

👥 Medicaid & Dual Status Indicators

Dual Eligibility Code: Flags whether the member is dually eligible for Medicaid — which can impact wraparound payments or SNP eligibility.

Low-Income Subsidy (LIS) Payment Fields: Captures any subsidies added to standard PMPM rates.

🎯 Why Should MA Plans Care?

Understanding the MMR file layout gives MA plans a huge operational advantage:

✅ 1. Validate CMS Payments

The file reflects what CMS thinks you should be paid — compare it with internal projections based on RAF, demographics, and enrollment history.

📉 2. Identify Revenue Leakage

Look for:

Records flagged with default risk factors (potential missed coding).

ARC codes that point to deletions or reductions in past payments.

Adjustments made for retroactive terminations or incorrect segment IDs.

📊 3. Support Audit Readiness

CMS, OIG, and internal compliance teams may audit based on these payment events. The MMR file provides the transactional trail you need to reconcile any discrepancies.

🧾 4. Reconcile with Claims & Chart Review

Link risk scores and payments to actual diagnoses documented in claims or EMRs. This can uncover coding gaps or documentation errors that impact revenue.

🛠️ Tips for Making the MMR File Actionable

Use ETL scripts or SQL loaders to parse the fixed-width format into a readable table.

Track ARC codes monthly to identify payment volatility.

Match MBI/HICN and segment IDs with internal systems for reconciliation.

Monitor Cleanup IDs and flags for large-scale CMS retroactions (e.g., overpayment recovery or OIG audits).

📎 Final Word

The MMR Detail File isn't just another CMS artifact — 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, understanding this file is essential to maintaining accuracy, avoiding revenue leakage, and staying audit ready.