Compare methods

	Population Momentum	Cohort-Component Projection
Field	Demography	Demography
Family	Process / pipeline	Process / pipeline
Year of origin	1971	2001
Originator	Nathan Keyfitz	Preston, Heuveline & Guillot
Type	Measure of latent growth from age structure after fertility reaches replacement	Demographic projection pipeline
Seminal source	Keyfitz, N. (1971). On the momentum of population growth. Demography, 8(1), 71–80.	Preston, S. H., Heuveline, P., & Guillot, M. (2001). Demography: Measuring and Modeling Population Processes. Blackwell. ISBN: 978-1-557-86451-2
Aliases	Demographic Momentum, Momentum of Population Growth, Keyfitz Momentum	Cohort-Component Method, Component Method of Population Projection, Age-Sex-Specific Population Projection, Kohort-Bileşen Projeksiyonu
Related	3	3
Summary	Population momentum is the tendency of a growing population to keep growing for decades even after fertility falls to the replacement level, simply because its age structure is heavily weighted toward young people who have yet to reach childbearing age. Introduced by Nathan Keyfitz in 1971, the momentum factor measures how much larger (or smaller) a population will ultimately become if fertility instantly drops to exact replacement. It explains why ending rapid population growth is not immediate: the built-in youthfulness of a fast-growing population carries growth forward long after birth rates stabilize.	Cohort-Component Projection is the standard demographic method for forecasting future population size and age-sex structure by explicitly tracking births, deaths, and migration for each age-sex cohort across discrete time steps. Systematically formalized in the textbook literature by Preston, Heuveline, and Guillot (2001), the method builds on foundational actuarial and demographic work dating to the early twentieth century and remains the workhorse technique used by national statistical offices and international organizations worldwide.