Systems and method for determining zero subject flow rate for correcting leak estimation in respiratory devices. Estimating leak in respiratory devices is necessary for proper ventilation of the subject. Correctly estimating leak allows synchronous triggering and enables accurate measurements of respiratory parameters such as tidal volumes and peak flows to be performed. The systems (10) and the method (100) herein provide a solution to correct (116) for errors in leak estimation methods through analysis (108, 110, 112) of flow rate of the pressurized flow of breathable gas generated (104) by a pressure generator (12) of a respiratory device, and identification or estimation (114) of the flow rate of the pressurized flow at which zero subject flow rate occurs, wherein adjustments to the employed leak estimation method can be thereafter made. The analysis and determination or estimation involve clustering methods, in particular analysis of a histogram of flow rate parameter values determined for individual sampling intervals, wherein the flow rate parameter value corresponding to zero subject flow rate is determined on the basis of the histogram and may involve determining a histogram bin or range value having the highest number of flow rate parameter values or mode of the histogram.
