MILESTONES BY THE BILLIONS

World population estimates milestones
Population (in billions)	1		2		3		4		5		6		7		8		9		10
Year	1804		1927		1960		1974		1987		1999		2011		2025		2040		2061
Years elapsed		123		33		14		13		12		12		14		15		21

The population of the world reached one billion in 1804, two billion in 1927, three billion in 1960, four billion in 1974, five billion in 1987, and six billion in 1999. The population of the world is projected to reach seven billion in 2011 or 2012, eight billion in 2025, nine billion in 2040, and ten billion in 2061.

There is no estimation on the exact day or month the world's population surpassed both the one and two billion marks. The days of three and four billion were not officially celebrated, but the International Database of the United States Census Bureau places them in July 1959 and April 1974.

        The United Nations did determine, and celebrate, the "Day of 5 Billion" (11 July 1987), and the "Day of 6 Billion" (12 October 1999). The International Programs division of the United States Census Bureau estimated that the world reached six billion on 21 April 1999 (several months earlier than the official United Nations day). The "Day of 7 Billion" has been targeted by the United States Census Bureau to be in July 2012, while the Population Division of the United Nations suggests some time in late 2011.