When the price of a food crop changes, the short term welfare variations of rural households is approximated thanks to the Net Benefit Ratio (NBR) defined by Deaton (1989). The NBR expression relies on a typology distinguishing between net sellers, net buyers and self sufficient households. We show that the typology’s criteria and the classic formula of NBR use i) produced and consumed quantities rather than real marketed volumes and ii) a unique price for selling and buying for all surveyed households. In this paper, we propose another definition of a net seller and a new NBR expression that allow to take into account market failures (MF) and price seasonality (PS), which are two very common features in developing countries. We used two sets of data (from Mexico and Mali), and found that, if considering MF and PS, (1) the household typology can be partly reconfigured and (2) the distribution of the NBR over the household income profile slightly changes.