The aim of this paper is to present a smartphone based system to assess daily energy expended in physical activ- ity (PA). Nowadays, sedentary li festyle is increasingly recog- nized as a serious, worldwide public health concern, because sedentary behaviors ar e associated to cardiovascular diseases and premature death. A smartphone application has been developed for data gathering from internal motion sensor, wireless wearable heart rate moni tor and user filled out forms. The data collected have been sent to a remote server to esti- mate the total energy expenditure (TEE), which has been determined by the sum of three components: basal energy expenditure (BEE), physical activi ty (AEE) and thermic effect of food (TEF). In this study, the subjects have used the devel- oped application for seven consecutive days, which represents a typical week. Then, a profil e of their daily TEE has been obtained. The presented system is a useful tool to generate personalized recommendations to maintain energy balance through more active lifestyle and healthier eating habits.