Each year, the Census Bureau's Population Estimates Program uses current data on births, deaths, and migration to calculate population change since the most recent decennial census and produces a time series of estimates of population, demographic components of change, and housing units. The annual time series of estimates begins with the most recent decennial census data and extends to the vintage year.
Population projections are estimates of the population for future dates. Projections illustrate possible courses of population change based on assumptions about future births, deaths, net international migration, and domestic migration.
While projections and estimates may appear similar, there are some distinct differences between the two measures. Estimates are for the past and present, while projections are based on assumptions about future demographic trends. Data users may find both an estimate and a projection available for the same date (e.g., July 2015), which may not agree. In such cases, estimates are the preferred data, unless the user's objective is to compare the number with others in the projected series.
Estimates and projections exist for the countries and areas recognized by the U.S. Department of State which have populations of 5,000 or more.