Every institutional claim on a UB-04 form includes a two-character medical billing claims frequency code. This small code tells the payer whether the claim is original, a correction, or a cancellation. Getting it wrong can lead to denied claims, delayed payments, or compliance issues. Understanding these codes is essential for hospital billers, outpatient facilities, and healthcare providers. This guide explains each code, when to use it, and how CMS rules apply.
What Is a Medical Billing Claims Frequency Code?
The medical billing claims frequency code is a one-digit or two-digit code entered in Form Locator 4 of the UB-04 (CMS-1450) institutional claim form. It is the third digit of the Type of Bill (TOB) code, a three-digit code that tells payers the facility type, the care classification, and the claim submission type.
For example, a TOB code of 111 breaks down as:
- First digit (1): Hospital inpatient
- Second digit (1): Inpatient Part A
- Third digit (1): Claims frequency code, Admit Through Discharge (original bill)
The frequency code is that third digit. It applies only to institutional claims, not to professional claims submitted on the CMS-1500 form. Understanding it is essential for anyone billing for hospitals, outpatient facilities, skilled nursing facilities, home health agencies, hospice, and other UB-04 billing entities.
Why the Medical Billing Claims Frequency Code Matters
Payers use the medical billing claims frequency code to determine how to process the claim relative to any previously submitted claims for the same patient and service period. Without the correct code:
- An original claim might be processed as a duplicate, resulting in denial
- A corrected claim might be rejected because the payer doesn’t recognize it as a replacement for the prior claim
- A cancellation might not be processed, leaving the original claim open and creating false AR balances
- A void submitted with the wrong frequency code could create audit flags suggesting intentional overbilling
According to CMS guidance, incorrect Type of Bill codes, including the frequency digit, are one of the most common causes of institutional claim rejections at the Medicare Administrative Contractor (MAC) level.
Complete Medical Billing Claims Frequency Code Reference
CMS defines the following frequency codes for institutional claims. The full list appears in the NUBC (National Uniform Billing Committee) Official UB-04 Data Specifications Manual, which is the nationally recognized standard for institutional claim formatting.
| Frequency Code | Code Name | When to Use It | Key CMS/NUBC Requirement |
| 0 | Non-Payment / Zero Claim | Reporting only, no payment expected; encounter data submission | Used in specific managed care encounter data submissions |
| 1 | Admit Through Discharge Claim | Original claim covering a complete episode of care from admission to discharge | Most common for inpatient and most outpatient original claims |
| 2 | Interim, First Claim | First bill for a patient still receiving care (e.g., long inpatient stay) | Required when the patient has not yet been discharged; episode ongoing |
| 3 | Interim, Continuing Claim | Subsequent bill while the patient is still an active inpatient | Follows a Frequency Code 2; patient still receiving care |
| 4 | Interim, Last Claim | Final bill when episode concludes; follows prior interim claims | Closes out the episode; marks patient discharge |
| 5 | Late Charge Only | Additional charges discovered after the original claim was paid | Must reference the original paid claim; not for denied claims |
| 6 | Reserved, Not Used | N/A, do not use | Reserved by NUBC; using this code causes automatic rejection |
| 7 | Replacement of Prior Claim | Corrected resubmission that replaces a prior paid or adjudicated claim | Must include ICN/DCN of prior claim; most common correction code |
| 8 | Void / Cancel of Prior Claim | Cancel a claim that was paid in error; remove it from the record | Must include ICN/DCN; used to return overpayment or fix billing error |
| 9 | Final Claim for Home Health PPS Episode | Used specifically for the Home Health Prospective Payment System final claims | Required for HHPPS, not used outside the home health context |
The Most Commonly Used Frequency Codes: Deep Dive
These codes tell payers what type of claim you’re submitting, whether it’s an original, a correction, or a cancellation, and ensure proper processing and timely payment. While there are several frequency codes, some are used far more often in daily practice. Below, we break down the most commonly used codes, starting with Frequency Code 1, and explain when and how to use each one effectively.
Frequency Code 1, Admit Through Discharge
This is the workhorse of institutional billing. Frequency code 1 means you’re submitting an original claim that covers a complete, closed episode of care, from the patient’s admission to their discharge. The vast majority of outpatient facility claims and most inpatient claims use frequency code 1.
When to use code 1:
- Outpatient facility services, same-day surgery, clinic visits, and emergency department visits
- Inpatient admissions where the patient has been fully discharged before billing
- Observation stays are billed as complete episodes
- Skilled nursing facility admissions (monthly billing cycles with no interim claims)
If you’re not sure whether to use code 1 or one of the interim codes, ask: Has the episode of care fully closed? If yes, use code 1.
Frequency Codes 2, 3, and 4, Interim Claims
Interim claims are used when a patient’s episode of care spans multiple billing periods, and the patient has not yet been discharged. This is most common for long inpatient stays, particularly in skilled nursing facilities, inpatient rehabilitation, long-term acute care hospitals, and inpatient psychiatric facilities.
The sequence is:
- Code 2 (Interim, First Claim): Submit this for the first billing period while the patient is still admitted. It opens the episode with the payer.
- Code 3 (Interim, Continuing Claim): Use this for all subsequent billing periods while the patient remains admitted. Each month in a long stay generates a Code 3 claim.
- Code 4 (Interim, Last Claim): Submit this when the patient is finally discharged. It closes the episode and signals to the payer that no more bills will follow for this stay.
Failing to submit the Code 4 final claim after a long inpatient stay leaves the episode open in the payer’s system, which can block future claims, delay AR resolution, and create audit issues.
Frequency Code 7, Replacement of Prior Claim
Frequency code 7 is one of the most important medical billing claims frequency codes to master, and one of the most commonly misused. It is used when you need to correct a paid or processed claim.
Key requirements for code 7:
- You must include the Internal Control Number (ICN) or Document Control Number (DCN) of the original claim in the appropriate field
- Code 7 voids the prior claim and replaces it with the corrected version in a single transaction
- It is used for corrections to any data element, patient demographics, dates, codes, charges, or provider information
- It is NOT used for adding charges discovered after payment, that is code 5 (Late Charge Only)
CMS’s Medicare Claims Processing Manual specifies that replacement claims must be submitted within the payer’s timely filing window from the date of the original remittance, not from the date of service. This distinction is critical: if you discover an error months after the original payment, your timely filing window for the replacement may be tighter than you expect.
Frequency Code 8, Void / Cancel of Prior Claim
Code 8 cancels a previously submitted claim entirely, as if it never happened. This is used when a claim was submitted and paid in error and needs to be removed from the payer’s record.
Common scenarios requiring code 8:
- A claim was submitted for the wrong patient
- A claim was accidentally submitted twice (duplicate billing, when identified by the provider)
- The wrong payer paid a claim and needs to be refiled under the correct primary
- A service was determined to be not covered, and payment needs to be returned
Like code 7, code 8 requires the original claim’s ICN or DCN in the claim reference field. Without this, the void cannot be processed correctly. Under the CMS 60-Day Rule, identified Medicare and Medicaid overpayments must be returned within 60 days, which often involves submitting a code 8 void as part of the repayment process.
Medical Billing Claims Frequency Code Errors and Their Consequences
Now that we’ve walked through the codes, let’s look at the billing errors these codes, when misused, can create.
Using Code 1 When Code 7 Is Required
Submitting a corrected claim with frequency code 1 instead of code 7 is one of the most common institutional billing errors. The payer receives what looks like a brand-new original claim and processes it as a duplicate of the previously paid claim—the result: a duplicate denial and a billing nightmare to unwind.
Always use code 7 for corrections to claims that have already been adjudicated.
Omitting Interim Claims (Codes 2 and 3) for Long Stays
Facilities that bill monthly for long inpatient stays sometimes skip the interim claim sequence, trying to submit a single original claim (code 1) for an episode that spanned multiple months. Most payers reject these claims because the dates of service exceed the billing period limits for a single claim.
Submit code 2 for the first month, code 3 for each subsequent month, and code 4 at discharge.
Failing to Submit a Code 4 Final Claim
When a patient is finally discharged after a long stay billed with interim claims, the facility must submit a Code 4 final claim. Without it, the episode remains open in the payer’s system indefinitely. This can block subsequent claims for the patient’s next episode, create phantom AR, and trigger audit inquiries.
Using Code 8 Without the Correct ICN/DCN
A void request submitted without the original claim’s ICN or DCN is a document matching failure. The payer cannot identify which claim is being voided, so nothing happens. The original claim remains open and paid, and the provider never succeeds in returning the overpayment.
Medical Billing Claims Frequency Code and Medicare Compliance
CMS has specific requirements for institutional claim frequency codes across all Medicare claim types. These are detailed in the Medicare Claims Processing Manual, specifically Chapter 25 for Completing and Processing UB-04 Claims.
For Medicare:
- Original claims (Code 1): Must be submitted within 12 months of the date of service for Medicare Part A claims
- Replacement claims (Code 7): Must include the claim’s Medicare Internal Control Number (ICN), found on the Medicare Summary Notice or 835 remittance file
- Cancellation claims (Code 8): Must be processed before any replacement claim for the same episode
- Interim claims (Codes 2–4): Required for services paid under PPS models with ongoing care (SNF, IRF, LTACH)
How Medicaid Handles Frequency Codes
Medicaid programs follow the NUBC UB-04 standards but may have state-specific requirements for frequency code usage. Most state Medicaid programs align with the standard code definitions, but billing timeframes and replacement claim windows vary by state.
In general:
- Timely filing windows for original Medicaid claims range from 90 days to 1 year, depending on the state
- Replacement and void timelines for Medicaid are often shorter than for Medicare. Verify your state’s specific rules
- Managed Medicaid (Medicaid MCO) plans may have their own claim frequency code requirements within the same NUBC framework
Practical Tips for Managing Frequency Codes in Your Billing Workflow
Given how much rides on this single field, frequency code accuracy should be built into your institutional billing workflow at multiple checkpoints:
Build Frequency Code Logic Into Your Claim Scrubber
Your claim scrubbing software should flag claims where the frequency code doesn’t match the billing context, for example, a code 1 submitted for a patient with open interim claims, or a code 7 submitted without a reference claim number. Many enterprise-grade clearinghouses and PM systems support this kind of contextual validation.
Maintain a Replacement and Void Log
Every code 7 and code 8 submission should be logged with the original claim’s ICN/DCN, the date of correction, the reason for correction, and the person who authorized it. This log is your documentation trail in the event of an audit or payer dispute.
Train Staff on Interim Claim Triggers
Billing staff managing long-stay patients need clear protocols: when to open an interim claim sequence, when to continue it, and how to close it properly at discharge. This is especially critical for SNF, IRF, and inpatient psych billing, where improper interim claim sequencing is a leading cause of payment delays.
Reconcile ERA Data to Catch Frequency Code Mismatches
Your 835 electronic remittance data includes claim adjustment reason codes that often indicate frequency code errors, for example, CO-97 (adjusted for a prior paid claim) or CO-16 (claim information missing or invalid). Building a workflow to categorize and trend these denial codes helps identify systemic frequency code errors before they accumulate.
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Frequently Asked Questions
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Where does the frequency code go on UB-04?
Enter the third digit ofthe Type of Bill in FL4. For example, TOB 131 means inpatient (1), Part A (3), Interim First Claim (1); payers reject mismatched entries instantly.
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Can you bill code 7 without the original ICN?
No, MACs auto-reject without DCN/ICN reference. Log originals pre-submission; this prevents 60% of replacement denials per CMS manual guidelines.
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What’s the difference between code 7 and code 5?
Code 7 replaces the entire prior claim; code 5 adds late charges only. Use 5 for discovered fees post-payment, avoiding full re-adjudication delays.
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How do SNFs sequence interim claims correctly?
Start code 2 month 1, code 3 subsequent months, end code 4 discharge. Miss code 4, payers hold final payments until the episode closes properly.
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Does Medicaid accept the same frequency codes?
Yes, all follow NUBC UB-04 standards. State timely filing varies (90-365 days); check portals for MCO-specific interim billing nuances.