Some animals are more equal than others. Even though this quote from animal farm was originally intended to expose the Sovjet Union, a similar line of fallacious reasoning is also used implicitly to defend excessive wealth in capitalism. No billionaire ever was more than an two orders of magnitude smarter, or more valuable than the poorest family in the world. Yet the difference in wealth is astronomical.

The richest persons in the world have a net worth in the order of magnitude of 10E11$. The poorest people in the world have negligible net worth, or debts.

More than 500 billion people live in extreme poverty (below $2.15/day) 1. At the billionaire side of the spectrum, the difference between income and profits becomes murky. For example, Elon Musk executed some stock options in 2021 that netted him an annual income of 23 billion $. The highest paid CEO's in the world are paid around 0.5 billion per year.

If the handful of billionaires at that level would spend 90% of their wealth and salaries to relieve poverty, it would not make a significant dent, but rest assured that the pyramid gets wider fast. There is plenty of money in this world, owned by people that don't need it. But that aside, let's look at the scale of the difference for a minute:

100 billion (the net worth of the richest people in the world) can sustain

We have a clear definition of human rights. The minimum of wealth should be the minimum needed to protect one's human rights. The right to education, privacy, adequate standard of living, require some level of wealth. If you're below that level of wealth, and there are no government funded reliefs to meet those rights, you have a right to sue your government for human rights violations. If your government fails to help you, you have a right to seek asylum in another country. If that country doesn't help you, you have a right to sue them. But obviously hiring a lawyer when you're starving and looking for food is not a practical option. That's why governments get away with shitfuckery, and people starve or drown in the sea.

The minimum should be at least two times the extreme poverty limit. Probably more is more fair.

If the wealthiest 50% of the population would fund this from their own pockets, it wouldn't cost them more than the price of a coffee per day.

A very often quoted research paper suggests that beyond a certain level of income (~$75.000/y at the time) happiness doesn't increase. If it doesn't make one happier, it is not needed, it seems to me. Later research suggests a logarithmic scale 1

Even if there's no plateau to happiness, it seems cruel and selfish to build your happiness on the unhappiness of many others. More than 10 times the previously established (and possibly not completely accurate) plateau should be more than enough to ensure legal limits to wealth do not cause unreasonable suffering.

This means 750k$/year should be the absolute maximum of income.

Let's set the maximum amount of wealth to this amount, times the number of years in a human life (100), which comes down to 75 million dollars. Anything above that could be taxed 100% without any human rights violations for sure.