It just happened that I read this while my levels of stupid were temporarily down and I now I got it. Yes, replacement level is 1 child per person born. No arguing that.
Still, for what I understand are the purposes of the OP, the question is how many kids per person of child bearing age. The world government cannot regulate the number of children a person dead at age 5 will have.
The OP has twice mentioned a world wide birth control policy, so I presume this means how many kids will you allow to have to a person willing and able to have them.
With a number such as 2.1 per couple (which I agree sounds like fudging) which we can double fudge to 1.1 per person, the problem remains of how to manage those .1 kids that everyone should have but cannot.
This might be a good time to give a second child to some to compensate for all those who do reach reproductive age but don’t want to have one (or want just one).
Alas, the OP hasn’t been back to read the responses so far and clarify his question.
As **Arnold Winkelried **deduced This is what I meant: What should the birthrate be, to make the population on earth exactly constant - meaning that world human population would be the same 100 years from now as it is today?
Well my example had an error near the end but it’s true that if people live longer then the birthrate has to be lower than exactly one child per person to keep the population constant.
See my post#10. In terms of a birth rate, 56 million births per year = about 8.4 births per thousand of population. In terms of a fertility rate, it = 1.07 children per couple. This would stabilize the world’s population right now.
These are very low numbers. They’re point-in-time numbers, as they must be to answer your question. Over time, as the population aged, the death rate would increase, and birth rates (and especially fertility rates, as there would be fewer younger women) would need to rise to keep pace.