Annualized Return = (((Final Investment Value\Beginning Investment Value)^(1/n)) - 1) * 100
An example of how this would work would go like this. Let's say you bought stock in XYZ, Inc. five years ago, and it was $10 per share when you purchased it. Five years later, it's now worth $75 per share (way to go!). Here's how we'd calculate the annualized return over that five-year period.
AR = (($75 / $10)^(1/5) - 1) * 100
AR = ((7.5)^(1/5) - 1) * 100
AR = (1.496 - 1) * 100
AR = 0.496 * 100
AR = 49.6%
You did OK on that one. But what if you wanted to see how consistent the returns were over those five years?
You use the same formula, but instead of over five years, just look at one year at a time. Below is a chart of how your stock performed across that five-year period.