The auditory P50/M50 ERP/event‐related field is subject to sensory gating, with partial suppression of the amplitude of the second of two (S1 and S2) clicks presented 500 ms apart. Schizophrenia patients have less gating, although quantification methods and associated effect sizes vary across studies using first‐admission and/or using chronic patients. The present study evaluated the impact of several methods of quantifying gating in first‐admission (FA) and chronic (CHR) schizophrenia patients and in healthy controls (HC). Magnetoencephalogram was measured in 35 FA, 58 CHR, and 28 HC during a paired‐click protocol. Sensory gating was quantified on sensor and source levels as a ratio (S2/S1) and as a S1‐minus‐S2 difference, with M50 amplitude scored relative to baseline and relative to M100 and to M40. Independent of quantification method, patients showed less sensory gating than HC, with medium‐to‐large effect sizes, without differences between FA and CHR. Results indicate that the frequently reported sensory gating deficit in schizophrenia is robust to variations in quantification methods and stage of disorder.