This projection includes persons whose usual residence is in the 50 States and the District of Columbia. It does not include overseas Armed Forces, their dependents, or other U.S. citizens residing outside the United States. The projection is based on the resident population, as enumerated in the 1990 census, and is not adjusted for net underenumeration. The projected series is revised once a month, so comparison of these projections over time may not reflect actual population change. Because it is an advance projection, it will generally not agree with current official estimates. Requests for official estimates of population produced by the Bureau of the Census for the nation, the States, or substate areas, as well as long-term projections for the nation and States, may be directed to POP@CENSUS.GOV, or sent in writing to Population Division, U.S. Bureau of the Census, Washington, D.C. 20233.
The "population clock" projection, shown above, is a near-term projection from a monthly series of population estimates. First, the population count from the last census is updated by adding births, subtracting deaths, and adding net migration (international migration, as well as the movement of Armed Forces and other U.S. citizens between the United States and abroad). These components of population change are estimates based on data obtained either monthly or yearly from various Federal agencies. Three-month projections of births, deaths, and migration are then derived from these "base-line" estimates. Each month, the monthly "base-line" estimates series is updated to the first day of the previous month; three months of projected population change are added, to produce a projection of population through the end of the following month. At the end of each year, a new series of population estimates, from the census date forward, is used to revise any or all postcensal estimates, as well as the three-month projections.
Once a series of monthly projections is completed through the end of the following month, the "population clock" numbers (such as the one shown above) are derived by interpolation. Within each calendar month, the daily numerical increase of population with time is assumed to be constant, subject to small discrepancies caused by rounding. Within 24-hour days, population increase is similarly assumed constant.