The 8-Minute Rule is a Medicare billing guideline used to determine how many units of time-based therapy services—such as physical therapy, occupational therapy, or speech therapy—can be billed during a patient session. According to this rule, a therapist must provide at least 8 minutes of a direct, one-on-one, billable service to charge for one unit. The total time spent on these services is then used to calculate the number of units: 8–22 minutes equals one unit, 23–37 minutes equals two units, and so on in 15-minute increments.