Globally, continuous urban expansion allied to land use/land cover transformation has reflected in negative impacts on ecosystem services and has made threats in the maintenance of human welfare. The value attached to the environment and its services (natural capital) is extremely difficult to assess quantitatively but becomes increasingly necessary to enable better decision-making. This paper addresses the carbon stocks approach, considering the modelling methodology carried out by the InVEST Carbon Storage and Sequestration model. Based on the ‘Paris-Saclay’ project implemented in the area of La Bonde (southwest of Massy, France), a new scenario was proposed for the region in order to assess the impacts, in terms of carbon storage variation, of this coming urbanisation. Three soil occupation assignment methodologies (‘priority order,’ ‘majority rule,’ and the newly proposed method ‘weighted values’) were used in the modelling. The total carbon stored evaluated using the ‘priority order’ criterion differed significantly, in the past and future scenarios, from those applying the ‘majority rule’ criterion (32.90% and 34.71%, respectively) and the ‘weighted values’ criterion (35.53% and 37.83%, respectively). The results demonstrated a better accuracy of the ‘weighted values’ criterion since it is the only one able to consider the complete area, without any approximation, of all land cover classes present in the region. Therefore, this study provides different modelling approach to precisely considering the spatial variability of ecosystem services and natural capital, dealing with the analysis of the urban land cover change impacts on carbon stocks that can be applied to other regions.