Yep, so far we've been talking about nominal sums without considering their real purchasing power.
The proper question of what is the sum of money that one can live off as a rentier to maintain a certain standard of living and how much needs to be saved for how long is... complicated.
Yup. The most sophisticated approach I've seen, which is clearly not actually sophisticated enough, is to guess at possible trajectories of future investment growth by some process along the lines of random sampling of past stock market returns, and then choose a sum that leads to you not running out of money in, say, at least 99% of those trajectories.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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