Blog Post

A Trilogy of Billing Blunders: Overbilling, Misbilling, and Underbilling

Overbilling is intentional; misbilling is not; underbilling is hurting your business. Learn if you're making one of these billing blunders.

Ryan Giebel
5 min read
November 29, 2022
image representing a trilogy of billing blunders: overbilling, misbilling, and underbilling
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Billing for physical therapy services is tricky, time-consuming, and nerve racking. After all, there are so many rules to follow, and it seems like those rules are constantly changing. That makes mistakes tough to avoid—and in many cases, you might not even know you’re making them. While an occasional billing error probably isn’t a huge deal, if you’re unknowingly messing up left and right, you could end up in hot water—putting your practice, your reputation, and your livelihood at risk.

Whether your billing slip-ups are accidental or intentional, actions have consequences—and apologies aren’t going to get you the money you deserve. That’s why it’s crucial that you understand the dos and don’ts of billing—before those don’ts end up taking a big chunk out of your bottom line. With that, let’s examine three of the most common ways rehab therapy practices can monumentally mess up their billing: 

  • overbilling, which is intentional, 
  • misbilling, which is accidental, and 
  • underbilling, which is just plain silly.


Overbilling is an intentional tactic used to wrongfully obtain higher payments. Within the rehab therapy industry, overbilling most often occurs in the following ways:

  • Upcoding: This fraudulent and abusive tactic involves a provider billing for codes and diagnoses more expensive and/or severe than what was appropriately diagnosed and/or performed. For example, upcoding can occur when a physical therapist bills for therapeutic activity (97530) instead of gait training (97116)—even though their treatment may more closely support gait training—because the former pays out more.
  • Overcharging: Similar to upcoding, overcharging is the act of charging additional units of the services the therapist performed or tacking on codes for services the therapist didn’t perform at all. 
  • Utilization abuse: This is the practice of scheduling extra visits or providing unnecessary services.

How to Avoid it


Here’s the pickle: overbilling is intentional. You know what you’re doing. Maybe you didn’t know it was wrong, but now you do. So, it’s time to put the kibosh on these fraudulent activities—otherwise, denied claims will be the least of your worries.

To shut down overbilling, you must provide medically necessary services specific to the patient’s treatment plan—and only bill for the services you actually provide. Curious about the definition of a “medically necessary” service? Per the APTA, the following factors determine if treatment is medically necessary:

  • A licensed PT determines it is so based on an evaluation;
  • It minimizes or eliminates impairments, activity limitations, and/or participation restrictions;
  • It is provided throughout the episode of care by the physical therapist under their direction and supervision;
  • It requires the knowledge, clinical judgment, and abilities of the therapist;
  • It is not provided exclusively for the patient’s convenience;
  • It is provided using evidence of effectiveness and applicable standards of practice; and
  • The type, amount, and duration of the treatment helps a patient improve function, minimize loss of function, or decrease risk of injury (or disease).

This list might not fall in line with every single “medically necessary” definition out there—after all, private payers can define it how they see fit—but it does provide more therapy-specific detail than most. It’s also on par with Medicare’s reimbursement requirements.


Does your practice currently suffer from a denial rate above 4%? Misbilling might be to blame. Misbilling—which includes manual errors, input oversights, and timing issues—typically occurs when your practice fails to:

  • Identify all billable codes.
  • Code to the highest level of specificity.
  • Create a clean claim. 

If your billing staff fails to identify all billable codes, then your payer will shortchange you. Of course, the ability to identify billable codes hinges on the accuracy of the documentation, so this error isn’t solely on your billers. Neither is coding to the highest level of specificity. This continues to be incredibly important with the use of ICD-10, where claim reimbursement depends heavily on the specificity of the diagnosis codes. As for creating a clean claim, you might be wondering what makes an otherwise clean claim dirty. In addition to missing or misused modifiers, consider:

  • Is the place of service accurate on the claim?
  • Is the claim deficient in certain information, like prior authorization or the effective period of time within which the pre-approved service must be provided for reimbursement to occur?
  • Are there mismatched totals or mutually exclusive codes?
  • Are there errors or typos resulting from the data-entry process?
  • Are you using outdated CPT codes, or does the claim list deleted or truncated diagnosis codes?

How to Avoid it

Accidents happen, and if your practice is suffering from any of these misbilling mistakes, then it’s time to clean up your billing workflow. Here’s how to get started on addressing the error of your practice’s misbilling ways:

1. Conduct an internal billing audit.

Monitor the documentation, coding, and claims creation processes. Scrutinize any denied claims to determine what caused the denial, and correct that problematic area.

2. Look for software or services that can help remedy issues.

Billing software or services can help you fix your billing woes, including misbilling. If your current billing service or software is allowing these problems to happen, then you might want to start shopping around. If you don’t currently use a billing software or service, you might want to consider it. It can eliminate a lot of these misbilling issues.

3. Level-set your team.

No matter what, meet with your team and get everyone on the same page. Explain the issues that are occurring and how they are affecting the business. Then, outline the consequences of making such mistakes and retrain where necessary.

4. Inspect every single denied claim.

According to the Healthcare Financial Management Association, up 65% of denied claims are never appealed or resubmitted by providers. That’s unacceptable. Payers often make mistakes and deny claims in error, so make sure you inspect every single denied claim. If you use a billing service, your reps should already be battling on your behalf and appealing denied claims. If you don’t use a billing service, then implement a denial management system, and task an employee with appeal duties.


Without a billing guru or intuitive billing software, many physical therapists in private practice may unknowingly be leaving money on the table. This can occur when folks don’t have a clear understanding of how the 8-Minute Rule and the rule of eights differ—and can be best utilized.

How to Avoid It

Most therapists have heard of the 8-Minute Rule as it’s the backbone of Medicare reimbursement for rehab therapy, but the rule of eights—which applies to commercial insurances that follow AMA’s CPT coding rules—tends to be a little more obscure. While we have several blog posts (not to mention a comprehensive guide) dedicated to this topic, I still think it’s valuable to review the main points.

Let’s start with the 8-Minute Rule. 

The following chart should look familiar to most therapists (as it’s likely their favorite cheat sheet for filling out visit charges for Medicare patients). 

In this chart, the numeric range in the left column represents the total timed minutes therapists spend treating patients, and the sum on the right represents the maximum number of units they can bill according to that time total. This pretty well sums up how to apply the 8-Minute Rule to your treatment—but, underbilling can still occur when therapists aren’t utilizing mixed remainders (a.k.a. leftover minutes) as they should. 

For those new to this concept, Medicare allows therapists to compile and bill for any leftover minutes that went: 

  • beyond the above referenced thresholds, but 
  • were less than eight minutes. 

For example, if you have an additional five minutes of therapeutic exercise (97110) and an additional three minutes of neuromuscular re-education (97112), these eight leftover minutes can be combined into one unit and applied to the service with the largest time total (in this case 97110 would get two units). Remember though, the total time still needs to meet the threshold requirements for total units (eight).

Now let’s tackle the rule of eights. 

If the payer being billed follows the rule of eights, then the mixed remainders principle does not fly. This rule strictly adheres to the Substantial Portion Methodology (SPM), where cumulating minutes or remainders is a no-go. As explained in this blog post, “in order to charge for a unit of service, you must have performed that service for a ‘substantial portion’ of 15 minutes (i.e., at least 8 minutes). That means that if your leftover minutes come from a combination of services, you cannot bill for any of them unless one individual service totals at least eight minutes.”

At face value, the rule of eights may appear to restrict billable units, but that’s not always the case. Let’s look at two hypothetical examples to learn how to shrewdly and legally define CPT codes in accordance with the rule of eights to improve reimbursements: 

  1. In one instance, if a therapist diversifies a treatment session so that it lasts 50 minutes in total, with five different treatment codes each totaling 10 minutes apiece, then the rules of eights dictates that the therapist can charge five units. 
  2. Another example—and perhaps a more common one—exists where a therapist charges two units for therapeutic exercise (say 23 minutes of 97110) plus three other treatments of therapeutic activity (97350), manual therapy (97140), and neuromuscular re-education (97112), each lasting at least eight minutes, then five units can be billed.

Both of these cases show where the rule of eights can yield more billable units than what Medicare’s 8-Minute Rule would allow. How ‘bout that?

Overbilling, misbilling, and underbilling happen more often than we think. In the whirlwind world of private practice rehab therapy, it’s hard to keep track of every single number, code, rule, or other regulatory factors. But honest, accurate billing is a must. So if you feel these principles slipping, it may be time to examine your billing workflow to see what adjustments can be done to stop mistakes and keep everyone on the clean-claim path.

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