From MarketWatch.com: What you need to retire and how to get there - MarketWatch
"This is a pretty easy number to come by, if dispiriting to some. If you expect to have a relatively safe retirement income of $60,000 a year, you will need $800,000 saved up by the time you retire.
I say dispiriting because not many folks at the edge of retirement are anywhere near that kind of number
. (We’ll explain how to get there in No. 2.) For now, assume you will collect, as a working couple, a payout from Social Security of $36,000 a year.
Your income gap is now just $24,000 a year, which you will draw from your retirement savings of $800,000 to close the gap."
Some very simple no-non-sense calculations to come up with the goal (in terms of amount) for retirement savings and how to get there.
It is also a good indication on how much (in percentage) one should invest in the stock market. If one has enough (or close to enough) in the retirement porfolio, why take a big risk in the dangerous stock market?