There are tonnes of information and calculators out there which can help you.
a. the AARP calculator,
b. the MarketWatch calculator, and the
c. “Ballpark Estimate” calculator
My own understanding is the 4% withdrawal rule and the passive income concept.
This article appears on Marketwatch, 28th Sept 2014.
There are 5 rules of thumb.
Are you more confused?! Good!