### Milestones

The following shows estimates of when each billion milestone was or will be met:

Population | 1 billion | 2 billion | 3 billion | 4 billion | 5 billion | 6 billion | 7 billion | 8 billion | 9 billion |
---|---|---|---|---|---|---|---|---|---|

Year | 1804 | 1927 | 1960 | 1974 | 1987 | 1999 | 2011 | 2024 | 2042 |

Years until next billion | 123 | 34 | 13 | 13 | 12 | 12 | 13 | 18 |

These numbers show that the world's population has tripled in 72 years, and doubled in 38 years up to the year 1999. Including some more estimates, the world population has been doubled or will double in the following years (with two different starting points). Note how, during the 2nd millennium, each doubling has taken roughly half as long as the previous doubling.

Population | 250 million | 500 million | 1 billion | 2 billion | 4 billion | 8 billion | |||||
---|---|---|---|---|---|---|---|---|---|---|---|

Year | AD 950 | 1600 | 1804 | 1927 | 1974 | 2024 | |||||

Years until next doubling | 650 | 204 | 123 | 47 | 50 | ||||||

Population | 375 million | 750 million | 1.5 billion | 3 billion | 6 billion | ||||||

Year | 1420 | 1720 | 1875 | 1961 | 1999 | ||||||

Years until next doubling | 300 | 155 | 86 | 38 |

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