Population projections are typically calculated using mathematical models that incorporate data on fertility rates, mortality rates, and migration patterns. These models are often based on historical trends and assume that these trends will continue into the future.

To make these projections, researchers first gather data on the current population, including age and sex distributions, fertility rates, mortality rates, and migration rates. They then use this data to create mathematical models that predict how these factors will change over time.

For example, fertility rates may be projected based on past trends and changes in social and economic factors such as access to education and healthcare. Mortality rates may be projected based on improvements in medical technology and changes in lifestyle factors such as diet and exercise. Migration patterns may be projected based on changes in economic opportunities and political stability.

Once these projections have been made, researchers can estimate future population growth rates and project when the population may reach a certain level, such as 10 billion. However, it is important to note that these projections are not set in stone and may change as social, economic, and political factors evolve over time.
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