A method (800) for estimating patient airway flow in a non-invasive ventilator system includes: (i) determining (830) an estimated gas flow； (ii) determining (840) a proximal pressure error value； (iii) compensating (850) for the determined proximal pressure estimate error value； (iv) compensating (854) for an error in the estimated gas flow； (v) determining (856) an estimated gas flow leak； (vi) monitoring (860) on a breath to breath basis for a leak； (vii) determining (870) a gas flow leak factor； (viii) adjusting (880) the estimated gas flow leak； (ix) detecting (872) a bias on the airway flow estimate； (x) determining (874) that the system is within a quiescent state of a breath； (xi) de -biasing (976) the estimated gas flow to drive the bias to near zero； and (xii) suspending (878) breath to breath bias correction on an immediately subsequent breath.
