Sure, so there's a few things to look at. The first is going back to the origins of the 4% number in the first place, the trinity study. The parameters for th

Sure, so there's a few things to look at. The first is going back to the origins of the 4% number in the first place, the trinity study. The parameters for that were a 30 year retirement period, and success was "not completely run out of money after 30 years, 95% of the time". If you extrapolate from that original study, if you retire for more than 30 years (FIRE includes retiring early), success drops from 95%. There's articles exploring that, e.g. https://www.fiphysician.com/safe-withdrawal-rate-early-retirement/ https://www.fiphysician.com/safe-withdrawal-rate-early-retir... https://www.madfientist.com/safe-withdrawal-rate/#:~:text=The%204%25%20rule%20is%20actually,average%20returns%20or%20nominal%20returns https://www.madfientist.com/safe-withdrawal-rate/#:~:text=Th... And then there are a variety of online calculators where you can play with the numbers yourself. The other elephant in the room is pre-Medicare healthcare costs.