The populations displayed on the clock are not intended to imply that the population of the world is known to the last person. Rather, the clock is the Census Bureau's estimate of the world population size and an indication of how fast it is growing. According to the current estimates, the world population reached 7 billion in 2012 and the new projections indicate that the 8 billion marker will be reached in 2025.

The world population estimates and projections used to produce these figures were developed by the U.S. Census Bureau based on analysis of available data on population, fertility, mortality, and migration. The analysis was performed separately for the countries or areas of the world with a population of 5,000 or more. Population estimates and projections analyses are based on census, survey, and administrative information. For most countries, and especially less developed countries, adjustment of the data is necessary to correct for errors, omissions, and inconsistencies in the data. Since the most recent data for each country are often at least 2 years old (and for most countries they are older), the population figures used for the clock are projections from those estimates based on assumed trends in fertility, mortality, and migration. As new data become available, all data are reevaluated and past conclusions may change.

The World midyear population and vital event estimates result from an aggregation of the figures for the individual countries and areas. The intermediate population estimates are based on a linear interpolation between successive midyear population figures. World vital events for different units of time are computed based on the number of months, days, hours, minutes, or seconds in the given year.

Figures may not add to totals due to rounding.