Part of estimating your needs in retirement and also in buying life insurance is to know your likely life expectancy. Although kind of morbid, one calculator to help you do this is The Longevity Game by Northwestern Mutual. You just answer a few questions about your lifestyle and family history, and it gives you a number based on their actuarial tables. Fun animations too!
It turns out my median life expectancy is 85, while my wife’s is 95. Not sure how she plans on enjoying a decade without me, but I have been working out more this week as a result. This site was found inside one of the 18 books I am trying to read simultaneously, Worry-Free Investing. The books uses it to show that for couples, there is a very good chance at least one of you will reach 95 or 100. So if you want to retire early, you basically need a portfolio that you can live off the income essentially forever while also having the principal keep up with inflation.