How do you calculate the return on investment for a single share of stock? For example, what would be the return/value of a single Google share now, if bought in January 2015?
To figure this out, you need to know the price per share then vs the price per share now. Google Finance will show you historical prices. For GOOG, the closing price on January 5, 2015 was $513.87. The price on December 31, 2015 was $758.88. Return on Investment (ROI) is calculated with this formula:
ROI = (Proceeds from Investment - Cost of Investment) / Cost of Investment
Using this formula, your return on investment would be 47.7%. Since the time period was one year, this number is already an annualized return. If the time period was different than one year, you would normally convert it to an annualized rate of return in order to compare it to other investments.