I suspect birthrate’s biggest factor is women’s financial independence and access to cheap and convenient birth control such as IUDs and birth control pills.

Birthrates are plummeting even for low income households, and I would bet it has something to do with Affordable Care Act of 2010 greatly increasing access to birth control by making it free. From the women I have spoken to, it is almost a no brainer to get an IUD.

https://www.statista.com/statistics/562541/birth-rate-by-pov...

I think societies are about the find out the real price of having babies now that they are not simply a byproduct of sex or women not having power.

> I think societies are about the find out the real price of having babies now that they are not simply a byproduct of sex or women not having power.

Can you expand on that, I'm not sure I follow?

Up until a few decades ago, women did not have a nearly foolproof way of preventing pregnancy while still being able to have dec. As well as having the power (financial independence) to say no to anyone pressuring them into getting pregnant. So now, the fertility rate will more accurately reflect a woman’s desire to get pregnant (at a certain age, at a certain income/wealth, given a certain set of possible partners, given a certain number of other children they already have, in a certain culture/time).

The caveats in the parenthesis are almost unnecessary though, since we are seeing declines in birthrate across all incomes/wealth levels around the world. I think we will see very, very few women choosing to have more than 3 kids, or even 3 kids. I actually only know of 1 couple with 3 kids, everyone else has 0, 1, or 2, and I am in mid 30s.

Decline in birthrate is a good thing, especially if we combine it with the reduction in mortality, and hopefully slowing aging and reversal of aging.

I suspect high income >200k/yr households are also highly correlated to high CoL locations. If you live in an SF 1 bedroom that costs 1.5 million dollars the marginal cost of an additional child is likely to be over a million dollars in the first 10 years of life. A family with exactly 200k/yr is at the entry point for financially achieving what would have traditionally been viewed as a middle class financial situation in the US e.g. owning a home, funding a retirement, taking regular vacations, paying for children's college etc. Even 1 child in a high CoL location can jeopardize these goals.

A relevant number would be the difference between income and the marginal cost per child.

There is a crossover point somewhere on the income/QoL scale where children go from utility to liability.

It's incredible recently, and still only in some countries, where children are in the liability area. By and large for all human history, children where a utility. More or less free labor to help support the family.