<P> The United Nations Population Fund designated 12 October 1999 as the approximate day on which the world population reached six billion . It was officially designated The Day of Six Billion . Demographers do not universally accept this date as being exact . In fact there has been subsequent research which places the day of six billion nearer to 18 June or 19 June 1999 . The International Programs division of the United States Census Bureau estimated that the world population reached six billion on 21 April 1999 . United Nations Population Fund spokesman Omar Gharzeddine disputed the date of the Day of Six Billion by stating, "The U.N. marked the' 6 billionth' (person) in 1999, and then a couple of years later the Population Division itself reassessed its calculations and said, actually, no, it was in 1998 ." </P> <P> On the Day of Six Billion, UN Secretary - General Kofi Annan was in Sarajevo, Bosnia and Herzegovina to monitor the Dayton Agreement . At midnight he went to Koševo Hospital, where Adnan Mević, born at 12.01 am, was named the symbolic 6 billionth concurrently alive person on Earth . He is the first son of Fatima Mević and Jasminko Mević and weighed 3.5 kg . </P> <P> The "Day of Seven Billion" was targeted by the United States Census Bureau to be in March 2012, while the Population Division of the United Nations suggested 31 October 2011, and the latter date was officially designated by the United Nations Population Fund (UNFPA) as the approximate day on which the world's population reached seven billion people . United Nations Secretary General Ban Ki - moon spoke at the United Nations building in New York City on this milestone in the size of world population, and promoted the website 7 Billion Actions . Ban Ki - moon did not choose a symbolic seven billionth baby, but several groups proposed candidates: Nargis Kumar of Uttar Pradesh, India, Danica May Camacho of Manila, Philippines and Wattalage Muthumai of Colombo, Sri Lanka . </P> <P> National or subnational governments have sometimes made similar designations based on the date estimated by a demographic agency . Some national milestones relate to citizens rather than residents . Commentators in countries with high immigration have pointed out that a population milestone may be reached by an immigrant rather than natural increase . </P>

When did the worlds population reach 4 billion