One "rule of thumb" for portfolio composition is to have the bond part of your portfolio equal to your age. For example, if you're 70 years old, then 70 percent of your portfolio should be in bonds. I don't follow this "rule." First, let's define portfolio for the purpose of this article. It is a collection of stocks, bonds, and other assets with the goal of sustaining a person in retirement. That is the goal of the portfolio: to supplement a retiree's income without running out of money. The amount of the portfolio depends on the needs and goals of the individual. There are hundreds of "rules" for portfolios. They can be simple, or complicated. Very popular currently with financial managers is Modern Portfolio Theory, which is based on mean-variance analysis, a mathematical framework for assembling a portfolio of assets such that the expected return is maximized for a given level of risk. Wow. What a mouthful. Ever since I studied fina...