It is estimated that the population of the world reached one billion for the first time in 1804. It would be another 123 years before it reached two billion in 1927, but it took only 33 years to rise by another billion people, reaching three billion in 1960. Thereafter, the global population reached four billion in 1974, five billion in 1987, six billion in 1999 and, by some estimates, seven billion in October 2011 with other estimates being in March 2012. It is projected to reach eight billion by 2024–2030. According to current projections, the world's population is likely to reach around nine billion by 2035–2050, with alternative scenarios ranging from a low of 7.4 billion to a high of more than 10.6 billion. Projected figures vary depending on underlying statistical assumptions and which variables are manipulated in projection calculations, especially the fertility variable. Long-range predictions to 2150 range from a population decline to 3.2 billion in the 'low scenario', to 'high scenarios' of 24.8 billion. One scenario predicts a massive increase to 256 billion by 2150, assuming fertility remains at 1995 levels.
|World population milestones in billions|
There is no estimation for the exact day or month the world's population surpassed each of the one and two billion marks. The days of three and four billion were not officially noted, but the International Database of the United States Census Bureau places them in July 1959 and April 1974.
The Day of Five Billion, 11 July 1987, was designated by the United Nations Population Fund as the approximate day on which world population reached five billion. Matej Gašpar from Zagreb, Croatia (then SR Croatia, SFR Yugoslavia), was chosen as the symbolic 5-billionth person concurrently alive on Earth. The honor went to Zagreb because the 1987 Summer Universiade was taking place in the city at the time.
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."
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 Mevic and Jasminko Mevic and weighed 3.5 kg.
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.
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.
|Country/nationality||Population||Born (date)||Name and surname||Notes||Foot-
|Munich||1m||15 December 1957||Thomas Seehaus||Awarded by Mayor Thomas Wimmer with a 1,000 mark savings account.|||
|United States||200m||20 November 1967||Robert Ken Woo Jr||Named by Life magazine, not the government. None named for 300m.|||
|Australia||15m||29 January 1982||Sally Hodgson||Awarded by Minister for Immigration and Ethnic Affairs Ian Macphee|||
|Indonesia||200m||4 February 1997||Wahyu Nusantara Aji||Complains that government promises of support were not kept|||
|India||1b||11 May 2000||Aastha Arora||speculation re Independence Day 1999 till Registrar demurred. Complains that government promises of support were not kept.|||
|Kyrgyzstan||5m||27 August 2002||Tynchtykbek Kuramayev|||
|Australia||21m||29 June 2007||Mia Ruby Templeton||Awarded by Treasurer Peter Costello|||
|Taiwan||23m||17 July 2008||Wu Cheng-en||certificate from Premier of the Republic of China Liu Chao-shiuan|||
|Auckland Region, New Zealand||1.5m||1 February 2012||Ramonah Patience Toomalatai||Welcomed by Len Brown the Mayor of Auckland|||
|Kazakhstan||17m||17 May 2013||Altynbek Eskaraev Алтынбек Ескараев|||
|Vietnam||90m||1 November 2013||Nguyễn Thị Thùy Dung||randomly chosen by the General Office of Population and Family Planning from among two dozen babies born that day|||
|Philippines||100m||27 July 2014||Chonalyn Sentino|||
|Wake County, North Carolina||1m||22 August 2014||Anderson Grace Hughes||Offered full scholarship by Wake Technical Community College|||
|Mongolia||3m||24 January 2015||Mongoljin Khatanbold|||
|Silicon Valley||3m||5 May 2015||Max Danner|||
|Utah||3m||24 October 2015||Sadie Christensen||By governor Gary Herbert|||
|Kyrgyzstan||6m||27 November 2015||Aylin Kojosheva|||
The ABS said it was unclear whether the 24 millionth Australian was a newborn or a migrant
He said the 23rd millionth person could be a newborn but could equally be a person coming to work in Australia or a returning backpacker who had been away for more than a year.