PIP: Women's life cycle involves reproduction, labor force, and inactivity. In developing countries with inadequate data, mathematical models can be used to analyze economic behavior of individuals and families in different stages of the life cycle. This study described a model and empirically tested the model on data from Paraguay. The model provided estimates of the mean age of women at first birth, the mean age of women at last birth, time spent in reproduction, and mean life after the birth of the last child for 1950-55, 1980-85, and projection to 2020-25. Values were generated from age-specific mortality and fertility rates. Simulations were performed with varying mortality and fertility schedules. The method was based on techniques developed by Krishnamoorty, who based his methods on models proposed by Hoem and Goodman, Keyfitz, and Pullum. The method was based on an assumption of a stable population with a fixed age pattern of mortality and fertility. An assumption was also that more and less fertile women had the same mortality risks, and fertility and mortality at any one age was applicable to all ages. The total and net fertility rates and life expectancy followed a linear pattern. Application of the method showed that the net fertility rate declined by 27% from 6.15 during 1950-55 to 4.49 during 1980-85, but the time spent in reproduction declined only by 15%, from 15.7 years to 15.9 years. The cause of fertility decline was not a shortened reproductive period, but birth spacing. Projections to 2020-25 showed a decline in the reproductive period of 7 years and a net fertility rate of 3.0 children per woman. When a simulation of one of the 8 UN models of fertility age structure was used to project future fertility, the results showed the reproductive period declined from 11.8 years to 9.7 years. When fertility was assumed to be 2.3, which was considerably lower than 4.49 during 1980-85, the results showed replacement level fertility during 2020-25 and an early age peak in fertility over a short reproductive period of 8 years. The simulation may represent future urban fertility patterns in Paraguay, which would affect labor force participation, which presently is low and stable at 20-23%.