I found an interesting site for those thinking about retirement. The site, called FIRECalc, includes a free on-line mathematical model that you can use. You can enter different amounts of savings, how much you would like to spend each year to see if your money would last. It models the US stock market history as if you had retired in the past and lived through the different bull and bear stock market periods. You can pick any time period..for example 30 or 40 years.
As a test I tried $100,000 with a withdrawal rate of 3 percent or $3,000 per year, with only 25 % being invested in the stock market. With a little trial and error I found that this amount would not last 40 years but it would last for 30 years.
The site discusses the impact of retiring close to the start of a severe bear market - the worst case scenario.
I would not base a retirement decision on just the results of the firecalc model, however I think playing with these types of models helps give one a feel for things.
My retirement decision included a good financial safety factor and a plan B, where if necessary, I would find another job or I would reduce my expenses. So far I have not seen the need to do either.
Here's a link: http://firecalc.com/