This study proposes a methodology to evaluate degrees of bilinguality. The objective is to quantify the concept bilinguality. Considering that the bilingual behavior should not be taken as one`s universalist or essentialist aspect, objective knowledge of statistics and probability, and formal methodology of data gathering, for example, do not cope with the subjective and contextual aspects of the bilingual manifestations. The orthodoxy and inflexibility of the available methodologies can not apprehend such a fluid concept as bilinguality. The propose of this study is to present Fuzzy Logic as a possible tool to measure bilinguality for it takes into account the observer/researcher`s individual perceptions and cultural experience for defining what constitutes the observed phenomenon. The truth of any affirmation is a matter of gradation. The methodology used was: 1) recording and transcription of interviews with bilingual individuals; 2) selection of life story narratives inside these interviews; 3) identification of the relevant variables for the analysis; 4) analysis of bilinguality using Fuzzy Logic Toolbox in MATLAB. The bilinguality of the individuals is analyzed in real everyday life situations, in contexts such as: familiar, social and professional. An important aspect to be considered is that, due to the fluidity of bilinguality, different factors and multiple variables compete to set up an analysis of bilingualism manifestations. Thus, we could prove mathematically, using fuzzy logic, what we might previously know based on our life experience: one individual presents different degrees of bilinguality, depending on the moment of their life they are.