Accurate measurement of induced abortion is necessary for understanding the fertility dynamics of a population and for making projections about the future. Changes in abortion rates can amplify or dampen the impact of changes in contraception. This paper presents a methodology for calculating marital induced abortion rates from observed marital fertility and contraceptive prevalence and for modeling the impact of substituting contraception for abortion on future fertility. The methodology is validated against observed abortion complications in three populations, and the impact of substituting contraception for abortion on expected fertility is demonstrated.