For those wringing your hands about 10% chance of failure, @CCCA from this forum has put a calculator that includes your very likely (at some point) death.
http://engaging-data.com/will-money-last-retire-early/
FWIW if you are male then at 85 you only have a 1/3 chance of still being alive to worry.
If you toggle the "death" off, then you get answers similar to all the other calculators that assume will live to an exactly specified age.
I repeat though, what calculators spit out is NOT a prediction of 10% chance of failure. That is an ENTIRELY nonsense concept.
What they produce is a percentage of incidence where a plan will fail under a specific set of circumstances based on market performance in the past. The assumptions in those circumstances don't mimic any actual human being's spending patterns, so it's not even remotely accurate.
Think about is from the reverse, if someone gets a 100% safe result, does that represent the level of risk that they'll never run out of money? Of course it doesn't! That conclusion would be insane. Utterly and completely irrationally insane.
There is so much that the calculator can't account for, and that's not even touching that it can't predict future market behaviour.
Let's assume that future markets behave, because that's the fundamental leap of faith we all need to make to retire. So let's assume they fluctuate exactly in line with the existing historical models. Cool.
Okay, what's still not accounted for is that spending can change, that the more money you spend, the more security you have baked in because you have the ability to dramatically cut costs.
If I'm living bare bones on a sub 20K budget, but I have enough buffer to generate a 100% success result, am I more secure than someone living a ridiculously lux life on 200K, but generating a 90% success rate?
Well, if shit hits the fan, my 20K budget has a few grand wiggle room here and there. Meanwhile, on my 200K budget, I can sell my McMansion at a major loss and one or two of my sports cars and end up with an additional lump sum a few times larger than my 20K budget self retired on in the first place.
All I have to do in my 200K life is give up my champagne and caviar lifestyle and drop my expenses down to a still luxurious sub 100K spend, and I'm suddenly drowning in more money than I could possibly need.
Now, let's look at personal risk, which is FAR more realistic than market risk anyway. Let's say I have a stroke that significantly compromises my function. This is a far more likely risk for most people than the markets doing something truly out of whack.
On my 20K budget, I don't have a huge ton of wiggle room to afford care, or maybe even more accessible living quarters, and could very easily end up bankrupt. On my 200K budget, I can sell all the cars, the McMansion, cancel the club memberships, skip the international first class travel, and divert my resources to securing what I need, while possibly even lowering my overall spending, despite buying the Porsche of wheelchairs.
I'm being extreme to make a point, but the point matters. People change their lives according to their financial circumstances, and they change their finances according to their life circumstances. This is the MOST predictable of human behaviors, and yet, the calculator has no capacity to account for it, and therefore no capacity to account for budget flexibility, which is ORDERS OF MAGNITUDE larger a factor in predicting success than most of what the calculators factor in.
Let's also examine the concept of the 10% failure as presented above. Let's say the calculator does predict the future and that somehow magically leads to a scenario where the person ends up 85 and out of money.
What kind of person just passively sits back and let's that happen? Certainly not the kind of person who runs their finances through a FIRE sim calculator.
Are we imagining that our mathematically inclined Mustachian retires with a tight budget because an online calculator spits out 90% and they shrug and say "good enough" and then never ever run those numbers again?
They just peacefully spend 4% +estimated inflation for years on end never checking their account balances or market performance until one day at 85 they try to pay for their blood pressure medication only to see "insufficient funds" on the machine, and then finally after decades login to their accounts and say "WTF?!!! An online calculator once said I would probably be fine! Holy shit, I guess this is that 10% I should have worried about!!!"
It's nonsense. Pure nonsense.