World Population Milestones Throughout History

Written by Marian Starkey, Vice President for Communications | Published: June 23, 2021

When Did the World Population Reach 1 Billion?

Until the Industrial Revolution began, birth rates and death rates were both very high, which kept the global human population relatively stable. In fact, it took all of human history, until around 1800, to reach 1 billion people. Modern medicine and sanitation played heavily in reducing mortality rates—especially among infants and children—but there wasn’t yet a reliable way to reduce fertility (the first modern contraceptive, the birth control pill, wasn’t introduced until 1960). The drop in mortality while fertility remained unchanged caused the beginning of what is now known as the J-curve (see below). With more people surviving to adulthood and then having kids of their own, the human population started growing exponentially.

When Did the World Population Reach Other Milestones?

It took 123 years to reach 2 billion, and only 33 years to reach 3 billion. The last several billion milestones (4, 5, 6, and 7 billion) have been reached in 14, 13, 12, and 12 years, respectively. We became a world of 7 billion in 2011.

Population Milestone Year Reached
1 Billion 1804
2 Billion 1927
3 Billion 1960
4 Billion 1974
5 Billion 1987
6 Billion 1999
7 Billion 2011

Nearly a quarter of the world’s population has been added to the planet since I graduated from high school in 1999. That was the year we crossed the 6 billion milestone, which is the same year that I learned about population challenges for the first time. I remember being completely stunned by how rapidly our population was growing while our planet and resource base remained the same.

Most of the growth since then has occurred in less developed countries—places already struggling to provide for their citizens, especially in the midst of the climate crisis (which has been disproportionately caused by people in high-income countries). Indeed, 95% of global population growth since 1999 has occurred in less developed countries.

World Population Growth Graph

The growth of the human population over time can be depicted by what is known as the Population J-Curve, which shows how sharply our population has risen in the last 200+ years. The graph above is one we created a couple years ago, when our population was 7.5 billion. In 2021, it’s estimated to be 7.8 billion, becoming 7.9 billion later this year or early in 2022.

The steep ascent over the past two centuries has created growing pains for families, communities, countries, and the planet. Consumption levels vary by individual and by world region, but everyone has infrastructure needs and contributes to environmental degradation to some degree. The more people who need food, water, shelter, health care, education, and employment, the more our agricultural systems, human institutions, and public infrastructure will need to grow and the more the environment and other species feel the strain.

When Will the Population Reach 8 Billion?

The United Nations Population Division projects that the world will reach 8 billion people in 2023—just two years from now—and that it will reach 9 billion in 2037 and 10 billion in 2057. Of course, these are just projections, and, as the chart above shows, projections don’t always come to pass. Without increased investment in voluntary international family planning programs and other initiatives that correlate with lower fertility (child survival, girls’ education, women’s empowerment, formal sector employment, etc.), we could be looking at a situation where the next couple milestones are crossed earlier than currently projected.