This paper discusses the various functions that have been used to predict the duration of insect life stages and presents a new algorithm for this purpose based on a polynomial function. The model was derived primarily for predicting biological events in the life history of the alfalfa weevil,Hypera postica(Gyll.), but gave equally precise simulations for three other species. Designed for a hand calculator, it is amenable to real-time weather acquisition and offers a practical alternative to the Stinner algorithm and other non-polynomial models for monitoring the development of insect pest populations.