Method for determining a stress level of an individual, depending on a physiological parameter of the individual, the value of which is liable to vary depending on the stress level of the individual, the method comprising the following steps: a) measuring a value of the physiological parameter ( x r ( t r )) , in various calibration periods ( t r ) using a sensor; b) defining a range of variation ( X r ) in the values of the physiological parameter which are measured in the various calibration periods; c) depending on the range of variation ( X r ), establishing a membership function ( f ), determining a stress level ( Sl ) of the individual depending on the value of the physiological parameter, the stress level determined by the membership function varying between: - a rest level, corresponding to a rest state of the individual; - a stress level, corresponding to a stressed state of the individual; - and at least one intermediate level, comprised between the rest level and the stress level; d) following step c), measuring a value of the physiological parameter ( x ( t )) in a measurement period, and determining the stress level of the individual ( Sl ( t )), during the measurement period, by applying the membership function ( f ) to the value of the physiological parameter measured during the measurement period; the method being such that, in step c), the stress level and each intermediate level are determined: - depending on values of the physiological parameters which are measured, in the calibration periods; - and depending on a distance (d(x(t), X r )) between the value of the physiological parameter measured in step d) and the range of variation ( X r ) defined in step b); the method being characterized in that , in step a), in each calibration period, the individual is considered to be in a rest state. a) measuring a value of the physiological parameter ( x r ( t r )) , in various calibration periods ( t r ) using a sensor; b) defining a range of variation ( X r ) in the values of the physiological parameter which are measured in the various calibration periods; c) depending on the range of variation ( X r ), establishing a membership function ( f ), determining a stress level ( Sl ) of the individual depending on the value of the physiological parameter, the stress level determined by the membership function varying between: - a rest level, corresponding to a rest state of the individual; - a stress level, corresponding to a stressed state of the individual; - and at least one intermediate level, comprised between the rest level and the stress level; - a rest level, corresponding to a rest state of the individual; - a stress level, corresponding to a stressed state of the individual; - and at least one intermediate level, comprised between the rest level and the stress level; d) following step c), measuring a value of the physiological parameter ( x ( t )) in a measurement period, and determining the stress level of the individual ( Sl ( t )), during the measurement period, by applying the membership function ( f ) to the value of the physiological parameter measured during the measurement period; the method being such that, in step c), the stress level and each intermediate level are determined: - depending on values of the physiological parameters which are measured, in the calibration periods; - and depending on a distance (d(x(t), X r )) between the value of the physiological parameter measured in step d) and the range of variation ( X r ) defined in step b); - depending on values of the physiological parameters which are measured, in the calibration periods; - and depending on a distance (d(x(t), X r )) between the value of the physiological parameter measured in step d) and the range of variation ( X r ) defined in step b); the method being characterized in that , in step a), in each calibration period, the individual is considered to be in a rest state. <EOS>