Investor Junkie has written a nice review of Personal Capital's retirement calculator. For those in retirement, or close to retirement, interested in a detailed analysis on whether they have enough to meet spending plans, the calculator appears to answer the outstanding questions. Note that it is free but does require providing a lot of information.
For what it is worth, my approach is considerably simpler. Take 4% on an inflation-adjusted basis, and check it every couple of years.
I was at an American Association of Individual Investors (AAII) a couple of years ago where a complicated Monte Carlo retirement analysis was presented. One of the audience members stood up and said his approach was to do what he had done all his life - calculate a reasonable withdrawal rate and then adjust his spending so that he lived within his means.
The bottom line is that some people want more detail and, thus, the Personal Capital calculator may be exactly what they are looking for. For others, the simpler approach will work better. I also have to admit I am prejudiced against spreading bank info all over the internet - but that's just me.
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