Determine the original stock price. This is the price of the stock when you purchased it. Let's say you purchased the stock for $50 per share.
Determine the current or ending stock price. The ending stock price is its price when sold, say, at the end of the year for tax purposes. Let's say you are considering the sale of your stock, but want to know its performance first. The current value of the stock is $60.
Determine the stock's earnings. This is the difference between the ending (or current) price and the original purchase price. The calculation is: $60 - $50 = $10.
Calculate the stock's performance. Divide the stock's earnings by the original amount paid. The calculation is: $10 / $50 = .20, or 20 percent. This is your return on investment.