A general rule of thumb for how much you can expect your investment portfolio to provide is approx. 3-4% per year. This, of course, depends on your portfolio allocation and other factors.
(example: $100,000 x 4% = $4,000 you can withdraw from your portfolio annually and reasonably expect your income to last the rest of your life.)
With a properly diversified portfolio and a start date of age 60 or older and a withdrawal rate of 3-4% your income stream should last a lifetime. What is a properly diversified portfolio? It is a portfolio of investments that are diversified by asset class, industry, geographic location and other factors. A negatively correlated portfolio can also help to provide proper diversification.