Two Questions for you guys that seems relevant to the thread.
First -- Most of the discussion here has been around the 4% SWR over 30 years, and then reducing the window to consider the first 15 years as the "critical phase".
What if the timeline is extended out to 50 years? An early retiree like MMM or someone around here might save enough to retire by age 35, and expect to live to 80 something years, which requires a portfolio to sustain for 50 years (lets ignore social security and side income).
Does stretching out the timeline from 30 to 50 years provide a portfolio benefit (longer time to earn returns, longer period to weather market downturns, etc.) or detriment (portfolio must last longer so withdrawal rate must be more conservative)?
Second -- if the first 10 to 15 years post FIRE are the critical phase for determining long term portfolio viability, would it not make more sense to shift to a conservative equities-bonds ratio during that window, and then open it up to something more aggressive after 10 to 15 years? For example, 60/40 for 10 years to limit any losses (would also necessarily put a cap on gains), and then shifting to a 80/20, 90/10 or all equities?
In the vast majority of cases, a 4% WR over 30 years leaves you with way more money than you started.
If you don't succumb to lifestyle inflation, 50 years won't matter, because your spending starts at 4%, and you increase it with inflation, but your portfolio grows faster than inflation, so then your WR drops to 3.5%, then 3%, then 2%, etc.
Those first 10-15 years are crucial in the 50 year part, too, because they're a time for your portfolio to grow, and weather the future storms easily. That's the answer to your first question--those first 10-15 years are still quite crucial.
As to the second, if you handicap your portfolio on that initial growth, in the 30 year timeframe it may not be as bad, because you only have 15 more years to get through. In the 50 year one, you still have 35(!) years to get through, after that first 15. Going more conservative when shooting for a 50 year timeframe may mean you weather the initial 10-15 year storms, but are in a much worse place to weather the later ones.
I'd rather be flexible with spending and earn a bit more (in those 10-15 years) than go with a more conservative portfolio (which may not make it).
Did that make sense? Not sure if I started rambling there. :)