> Officially before the one child policy they were at 800 million. After 30 years of 1 child policy somehow they were at 1.2 billion. The math isn't mathing.

Even if I take your numbers at face value, it is absolutely possible for this math to math. To simplify massively, if the average person dies at 80 years old, the population growth today depends on the number of births 80 years ago, compared to today. Not 30 years ago. The population may have grown massively between 30 and 80 years ago, so that the absolute number of births remains high, despite a low birth rate.

Yep, people don't understand moving averages with a wide range. The old population getting older massively changes demographics. You start looking like Japan where a huge portion of the population is above retirement age.

And this fits for China where the standard of living has massively increased. What would throw off most Americans is that in 1962 the average life expectancy in China was only 50 years old, and has increased to roughly 78 today. 28 additional years of life is huge and it was so rapid that it would create a massive increase in population.

This also reverses causality on the one child population rule. They didn't add the rule because their population was huge at the time, it was added because increased life expectancy with nothing else would have increased their population now to something like 1.7 to 2 billion.

And inverse is also true, so that China’s population is currently shrinking and aging, despite the “1 child” policy being abandoned a decade ago.