Phenological stages are widely used in crop models as starting points for most processes based on leaf, biomass and yield growth. In soft wheat in particular, the appearance of the last leaf on the main shoot is a mandatory stage for crop protection strategy, since this stage alone, contributes to up to half of the carbon allocated to the grain. We propose to build a mechanistic model for simulating flag leaf appearance stage (FLAS) in soft wheat, consisting in three main steps ; (1) estimation of floral transition stage, that we assumed to be the stage corresponding to the moment when primordia are determined as future spikelets or leaves ; (2) computation of a dynamic phylochron along crop cycle, based on photoperiod and thermal time scales ; and (3) calculation of all leaf stages from pre-formed primordia to the last leaf to appear (FLAS).