Systems slow breathing with positive pressure therapy. In embodiments, a current interim breathing rate target is set, and periodically magnitude of a variable pressure waveform scaled to the current interim breathing rate target is increased if breathing rate is greater than the interim rate target to lengthen breath duration. The magnitude of the pressure increase may be a function of the difference between the interim rate target and the breathing rate. The interim rate target may be reduced in response to slowing breathing rate. The waveform cycles, inhalation to exhalation, when airflow decreases to a cycle threshold. Different interim rate targets have different cycle threshold functions that allow easier cycling as the interim rate targets decrease. Similarly, the waveform triggers, exhalation to inhalation, when airflow increases to a trigger threshold. Different interim rate targets have different trigger threshold functions that allow easier triggering as the interim rate targets decrease.