Rice (Oryza sativa L.) is an important food crop for more than half the world's population. It grows best under shallow flooded conditions. For establishing a healthy rice stand in a flooded field, the seedlings of the crop are first grown in nurseries and then transplanted into the field. At a specific location, transplanting dates determine how growing conditions later in the season will affect the rice crop. Dry conditions after ripening, favorable to maintaining the quality of rice through harvest, may be more or less likely to occur, depending on the transplanting date selected. The objective of this study was to determine optimum transplanting dates for rice at five locations in Kerala, a monsoon-affected state in southern India. Optimal transplanting dates were derived based on two approaches: (i) probabilities of rainfall events using ClimProb, a PC-based software package, and (ii) target yields simulated by the CERES-Rice v3.0 crop growth simulation model. Under rainfed conditions, the optimum transplanting dates were from the 23rd to 26th week for multiple cropping in a year, and from the 26th to 32nd week for a rainfed monocrop. The ClimProb approach used here can be adopted for use elsewhere if climate data are available, and the model approach can also be adopted if specific weather, soils, and crop information is available.