If you retire at 65 and live to 100, you’re supposed to live on $20k a year pre-tax (assuming you’re withdrawing from a pre-tax account like a 401k)?

That isn’t going to work.

$800k does seem a little low, but a lot of that depends on your living situation. Even with $800k you should be able to live off of way more than $20k/year. You can get $20k/year just by buying treasury bonds and collecting interest, maybe even double that potential income if you think that social security will still exist in its current form when you're retire.

More importantly, once you're in your 80s it's probably safe to start whittling away at that principle.

Those numbers seem to assume none of it is invested...

You can get, averaged over several years, something like $50k/year from that.

And if the market crashes when you are retired? What are you supposed to do?

I don’t think it’s sound advice to keep your retirement in stocks when you’re actually in retirement...

You only need to keep "crash /recovery" money around, which is a risk because you don't know how long that is. 5? 10?

But you also don't know how long you'll live for, so to have your money doing nothing for 20/(30?!) years could hurt. My wife's grandmother is 99. That's a long time in low-growth near-cash.

if that money is coming from selling off some equities, it would likely be long term capital gains, which... I believe the first $x000 are taxed at 0%.

Your point about $20k not being much is true, but I also would presume that someone who's saved that much probably would have some social security coming in, at least doubling that.