The $40k figure is from here (obviously there's no sharp cut off, but we chose a figure that's roughly right for convenience): https://80000hours.org/career-guide/job-satisfaction/#money-...

And then even more detail here: https://80000hours.org/articles/money-and-happiness/

It's $40k of consumption. So if you'd want to save $6k as well, then you'd need to earn $46k.

Our advice is addressed at college graduates. The average grad makes $68k p.a. over their lifetime. (Source in the first article I linked to).

If you're reading HN, then it's likely you can earn more. The median software engineer makes $100k, and similar with other tech jobs (that's from the BLS).

I agree it's much harder to give money if you earn below the median income in the US, though it's hardly impossible. The average low income American already gives 3% on average (source in the OP), so my 1% is actually less than the average.

Moreover, almost everyone in America is far wealthier than the world median. Even if you only earn $10k, you're 7x wealthier than the world median. Source: https://www.givingwhatwecan.org/get-involved/how-rich-am-i/ (That's PPP adjusted)

So while I agree if you're poor in US it probably wouldn't make sense to give to other poor in the US, it could still be worth giving to the global poor.