Method for estimating the pressure (Pass) in a vacuum chamber of a vacuum brake servo of a motor vehicle, the vehicle comprising: - at least one braking device controlled by the pressure (Pmc) of a brake fluid; - a master cylinder, which controls the pressure (Pmc) of the brake fluid and which is actuated by an actuating member movable between a rest position and an end actuation position; - a brake servo, which is arranged between the actuating member and the master cylinder to amplify the force of the actuating member by means of a vacuum, provided by a chamber held under vacuum, by vacuum means, to an assistance pressure (Pass); - a means for detecting the displacement of the actuating member beyond an intermediate guard position; - a pressure sensor, which is designed to measure the braking pressure (Pmc) of the brake fluid; the method comprising: - a first step of calculating the braking pressure, which is repeated cyclically; - a second step of determining the amplitude (ΔPmc) of a reduction in pressure, during which the maximum (Pmc_max) then the minimum (Pmc_min) reached successively by the braking pressure are stored, and during which the amplitude (ΔPmc) of the reduction in braking pressure is calculated by establishing the difference between the maximum (Pmc_max) and the minimum (Pmc_min); - a third step, which is triggered at the end of the second step and during which the increase (Conso) of the pressure (Pass) in the vacuum chamber is estimated as a function of the amplitude (ΔPmc) calculated in the second step, an updated assistance pressure (Pass_actu) being calculated by adding said increase (Conso) to an initial assistance pressure (Pass_ini), characterized in that it comprises a fourth step of calculation of the return to a minimum assistance pressure (Pass_min) in the chamber, which is triggered at the end of the third step and during which the reduction in pressure created in the chamber by the vacuum means is calculated. - at least one braking device controlled by the pressure (Pmc) of a brake fluid; - a master cylinder, which controls the pressure (Pmc) of the brake fluid and which is actuated by an actuating member movable between a rest position and an end actuation position; - a brake servo, which is arranged between the actuating member and the master cylinder to amplify the force of the actuating member by means of a vacuum, provided by a chamber held under vacuum, by vacuum means, to an assistance pressure (Pass); - a means for detecting the displacement of the actuating member beyond an intermediate guard position; - a pressure sensor, which is designed to measure the braking pressure (Pmc) of the brake fluid; the method comprising: - a first step of calculating the braking pressure, which is repeated cyclically; - a second step of determining the amplitude (ΔPmc) of a reduction in pressure, during which the maximum (Pmc_max) then the minimum (Pmc_min) reached successively by the braking pressure are stored, and during which the amplitude (ΔPmc) of the reduction in braking pressure is calculated by establishing the difference between the maximum (Pmc_max) and the minimum (Pmc_min); - a third step, which is triggered at the end of the second step and during which the increase (Conso) of the pressure (Pass) in the vacuum chamber is estimated as a function of the amplitude (ΔPmc) calculated in the second step, an updated assistance pressure (Pass_actu) being calculated by adding said increase (Conso) to an initial assistance pressure (Pass_ini),