Observed on July 11 every year since 1989.

Notes on the World Population Clock (April 25, 2018):

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 Census Bureau’s International Data Base estimated that the world population reached 7.5 billion on June 13, 2018.)

From International Programs:

The International Data Base (IDB) was developed by the U.S. Census Bureau to provide access to accurate and timely demographic measures for populations around the world. The IDB provides estimates and projections for 228 countries and areas which have populations of 5,000 or more and as recognized by the U.S. Department of State.

The link above shows Demographic Overview and other select reports for up to 25 years from 1950 to 2050 by single country, multiple countries, or select regions. UN Regions include the world in these four categories:

• More Developed Countries
• Less Developed Countries (LDCs)
• LDCs, without Least Developed Countries
• Least Developed Countries 

Source: Demographic estimates prepared by the Census Bureau's Population Division for the International Data Base.

This viewer provides four 2020 demographic indicators for the world's countries with a minimum population of 5,000 in 2020: total population, growth rate percent, life expectancy at birth, and infant mortality rate.