Obviously there are a lot of uncertainties involved but nonetheless, researchers have come up with an answer that they believe to be reasonably accurate based on the available information.
Researchers at the Population Reference Bureau (PRB) consider the beginning of human history to be 50,000 BC which is when modern Homo Sapiens appeared. They take this date from the United Nations Determinants and Consequences of Population Trends.
Researchers then face the problem of estimating population expansion since 50,000 BC – taking into account things like low life expectancy, infant mortality rates, climate changes, wars, plagues, food supply issues, and a multitude of other problems.
Nonetheless, in 2011 they came up with what they consider to be as accurate an answer as anyone has been able to provide to the question of how many people have ever lived on Earth…
As of 2011, 108.2 billion people had been born. Taking away the roughly 7.4 billion people currently living on the planet, that means 100.8 billion have died before us.