Optimizing wheat phenology is of major importance in order to reach yield potential and to avoid within-season stress at critical periods. Identifying loci that determine heading date of wheat cultivars and developing models to predict genotype performances under different pedo-climatic scanrios will assist optimization of phenology through breeding. In this study, association genetics for heading date (in thermal units °Cd), earliness components and simulation model (APSIM) phenology parameters from a panel of Australian cultivars and breeding lines identified loci with stable effects on heading date and its components, providing new insights into the genetic architecture of this trait in the Australian germplasm. Seventy-three genomic regions showed stable QTL with r2 ranging from 2 to 18% across the trait components and parameters Few major regions with large and stable effects were detected: one region on 1A for photoperiod sensitivity (PS), the Ppd-D1 region on 2D for PS and earliness per se (EPS), one region on 4B (nearby, but independent of Rht-B1) for PS, the Vrn-A1 region for vernalization requirement (VR), one region on 5B (independent of Vrn-B1) for VR, one region on 5D (independent of Vrn-D1) for VR and one region on 6B for EPS. QTL-based model parameters were used to simulate heading dates in different location × sowing date across the Australian wheat belt for a validation dataset of independent genotypes. Relationships between average observed and predicted heading dates for four main regions of the Australian wheat belt showed good performance in prediction of independent lines from QTL information alone (r2 0.69 to 0.91). This model using only genetic information, allows the simulation of heading date, of different genotypes under various pedo-climatic scenarios and the identification of target ideotypes for these scenarios. This makes it a possible decision making tool for breeders to optimize heading date and help adapt to anticipated climate changes.