Methodology and Assumptions for the Population
Projections of the United States:
1999 to 2100
_________________________________________________________
Population Division Working Paper No. 38

Frederick W. Hollmann,
Tammany J. Mulder,
and Jeffrey E. Kallan
Population Projections Branch
Population Division
U.S. Census Bureau
Department of Commerce
Washington, D.C. 20233
(301) 457-2428
www.census.gov
Issued January 13, 2000

ABSTRACT
This working paper discusses the methodology and assumptions used to develop the recently released
projections of the population of the United States from 1999 to 2100. The new series includes projections
of the population by single year of age, sex, race, Hispanic origin, and nativity. While the basic
methodology used to produce these projections is the same as in earlier Census Bureau national population
projections, there have been changes, in both the time horizon and reference dates of the projections, as well
as in the specific methods used to estimate population change. The extension of the series to 2100 carries
the projections 20 years further into the future than any series previously issued by the Census Bureau.
For the first time, projection results include a break on nativity, defined dichotomously by the presence or
absence of U.S. citizenship at birth, as well as its cross-classification with other variables. Also new with
this series is the projection to quarterly reference dates, allowing users to view the national population
seasonally, or simply to select annual reference dates other than July 1. In addition, international migration
in the new series is allowed to vary over time, remaining somewhat lower than the constant value in the
previous series for the first two decades of the century, but reaching considerably higher levels than in the
previous one after 2020. Fertility rates in both models are allowed to change very little over time.
However, fertility rates by race and Hispanic origin are allowed to converge in the new middle series,
whereas in the previous middle series they remained constant within race and origin category. Finally, the
new mortality assumptions show more improvement in life expectancy for all racial and Hispanic origin
groups, except the non-Hispanic White population, than did the assumptions of the previous projection
series.