If you are considering retirement, and you are wondering if your investment assets will last for the rest of your live, there is a cool site that will calculate it for you in a simple format. The site, Zunna Calculators, has you pick just four options: your investment horizon in years (in other words, how long you anticipate withdrawing money from your accounts), the account ending value goal ('Don't Go Broke' if you eventually deplete your account by the time you pass away), the required historical success rate (or how certain you want to be of success). and desired annual withdrawal amount.
For example, if you plan on a 30 year period of retirement and you want to be certain that you don't want to go broke before you die, assuming you want a minimum of $50,000 a year to live on, you would need investment assets in the amount of $1,253,133. The maximum sustainable withdrawal rate is 3.99% and the Optimized Portfolio that the site gives is 62.05% large cap stocks and 37.95% US T-Bills.
I have no connection to this site whatsoever, just thought it might be of interest.