Your asset allocation is a key decision you need to make as an investor, and this rule makes it easy to decide. Here's how it works.

Using age to determine your stock-bond mix is the default for retirement investing. But now retirement can last 30 years or more, it's time to rethink the rules.

How much money should you put into stocks? A popular asset allocation by age model invites investors to let their age guide their investments. As the theory goes, younger investors should put more of ...