The U.S. population clock is based on a series of short-term projections for the resident population of the United States. This includes people whose usual residence is in the 50 states and the District of Columbia. These projections do not include members of the Armed Forces overseas, their dependents, or other U.S. citizens residing outside the United States.
The projections are based on a monthly series of population estimates starting with the April 1, 2010 resident population from the 2010 Census.
At the end of each year, a new series of population estimates, from the census date forward, is used to revise the postcensal estimates, including the population clock projections series. Once a series of monthly projections is completed, the daily population clock numbers are derived by interpolation. Within each calendar month, the daily numerical population change is assumed to be constant, subject to negligible differences caused by rounding.
Population estimates produced by the U.S. Census Bureau for the United States, states, counties, and cities or towns can be found on the Population Estimates web page. Future projections for the United States can be found on the Population Projections web page.