The primitive (single oviposition period) method for determining the finite rate of natural increase (Λ) of an insect species which lays all its eggs quickly is described, together with a summary of a more accurate method introduced by P. H. Leslie and L, C. Birch of calculating the infinite (infinitesimal) rate of increase (r) of any species. The parameterris the natural logarithm of the parameter Λ. Two methods of simplifying this more accurate method are discussed and illustrated by six examples which are used to compare the results given by all four methods.The first modification of the Leslie‐Birch method provides a means of representing a long oviposition cycle by a single figure so that the final calculation resembles the primitive single period method. The oviposition period is divided into a number of convenient unit periods, and using a table of weighting factors provided, the number of eggs laid in each of these unit periods is converted into the number of eggs required to be laid in the first of these unit periods of oviposition to make an equivalent contribution to the rate of increase. The equivalent oviposition figures for all the unit periods are summed to provide one figure which represents the observed egg number and pattern.The second modification provides a means of representing the observed egg pattern by a constant rate of oviposition. This requires the same table of weighting factors but also needs a series of charts which are provided. This method usually gives a good answer at the first attempt, whereas the first modification usually requires two trial and error solutions to give an accurate estimate ofrand hence of Λ. Two of the examples show how the methods may be used for species for which information is scattered in the published literature. The minimum requirements for estimation ofrare information on the length of the developmental cycle, the rate of egg output of adults, mortality of all stages and the sex r