If you are retired and 3 years spending is 25% of your total stash that equals an 8 percent plus withdrawal rate!
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Did I misunderstand the metrics of your post?
You assume OP is retired because they are asking a question of retirees. I think it is more likely that OP is a few years away from retirement.
The actual percentage in my case is probably less interesting than how I arrived at my answer.
What I do is track my spending in Quicken which tells me how much it costs me to live. Call this $X.
I then use life expectancy information and my current age to decide how much longer I think I will live (I just use 50th percentile numbers here). Currently I am 50 and use 40 years.
I think the future will be somewhat better than the past, so I assume a 95% historically safe SWR.
I plug my statistics and 40 years into FIREcalc and then use the investigate tab to adjust the spending level to 95% historically safe levels. This is much higher than $X, by the way.
I then look at the asset allocation sensitivity at that level of spending. I pick the AA with the highest historically safe success rate. If there are ties, I'll pick the highest stock allocation among those ties. This is because I have a fairly high risk tolerance and I am an optimist and I have kids.
At this point I have answered the question, "If I took my current situation and ratcheted my spending up to the most that I would feel safe doing, what should I then set my AA to in order to be most safe, from a historical perspective, over my remaining lifetime?"
For me currently, that answer is 10% bonds.
I then take my current spending and multiply it by 1/4.08% to see what portion of my portfolio is "mine". Anything above that amount will be my kids' money, so that is 100% stocks as I think they will inherit in 30 years or more, and again, I'm an optimist.
Of "my" portion of the portfolio, I multiply that by the bond ratio in the AA above (10%) to see what amount I should have in bonds.
Since I am currently spending 0.41% of my FIRE portfolio, this means my target is 0.41% * 10% / 4.08% = 1.01% in bonds. If my spending were to increase, as it might, I would consequently allocate more to bonds. As I age and my plan duration years lessen, the historically safe AA to bonds would increase somewhat, so that would also have me put more in bonds.
Currently I'm actually at 6.53% bonds. I also have a few months expenses in checking/saving.
When the stock market next goes south, as it inevitably will, my plan is to rebalance occasionally, withdraw as needed, and plan on history being no worse than the past (probably better - I'm an optimist). I expect I will naturally become a little nervous and cut back some, like everyone else.
In 20 years I'll get Social Security. 60% of my Social Security will basically cover my current expenses. (I derate SS to 60% of my actual benefit.)
Single. Paid off house. Kids' college covered. No large expenses on the horizon. Theoretically willing to work a job if needed to keep the lights on. Have a number of contingency plans both on the income and expense side.