The 8-Minute Rule is a Medicare billing guideline used to determine how many units of time-based therapy services can be billed during a patient session. According to this rule, a provider must spend at least 8 minutes performing a billable, one-on-one, time-based service to charge for one unit. The billing then follows 15-minute increments—8 to 22 minutes equals one unit, 23 to 37 minutes equals two units, and so on. This rule ensures that therapists, such as physical, occupational, and speech therapists, are reimbursed accurately based on the actual time spent with the patient.