CORECS is a widely applicable finite time-step (At), numerical population simulation model. The model was designed for applications to a tropical context by utilizing continuous versus discrete decision variables. It was specifically designed to produce stochastic age-independent population probability density distributions peculiar to the specific continuous spawning and recruiting life history patterns typical of tropical and subtropical marine fish stocks. Computations are performed on any portion of a whole time unit (typically 1-year) desired. Computations are summarized per At, and also over the whole unit.