You own 10 shares of company ABC at $50 per share. You believe the stock price of ABC is grossly overvalued and is going to crash sometime soon. You are so convinced that the stock will crash, you come to me, and ask to borrow my ten shares of ABC and sell them at the current market price for $50. I agree to lend you my shares as long as you pay me back ten shares of ABC at some point in the future. You take the ten borrowed shares, sell them for $500 (10 shares x $50 per share = $500).
The following week, the price of ABC stock falls to $20 per share. You call your broker and tell him to buy 10 shares of ABC stock, at the new price of $20 per share. You pay him the $200 (10 shares x $20 per share = $200). A few days later, you pick up the shares of ABC and bring them by my office. “Here are the ten shares I borrowed,” you say as you put them on my desk.
Do you see what happened? You borrowed my shares of ABC, sold them for $500. The following week, when ABC fell to $20 per share, you repurchased those ten shares for $200 and gave them back to me. In the mean time, you pocketed the difference of $300.
The Speculative Nature of Shorting Stock
What if the price of ABC stock had risen? The person shorting stock would have had to buy back the shares at the new, higher price, and absorb the loss personally. Unlike regular investing where your losses are limited to the amount of capital you invest (e.g., if you invest $100, you cannot lose more than the $100), shorting stock has no limit to the amount you might ultimately lose. Famed investor Ben Graham told us there is nothing stopping an overpriced stock from becoming more overpriced. In the unlikely event the stock had shot up to $1,000 (which actually happened to shares of Northern Pacific during a short squeeze in 1902), you would have had to purchase ten shares at $1,000 a share for $10,000. Taking into account the $500 you received from selling the shares earlier, you would have lost $9,500 on a $500 investment.
In order to begin shorting stock, you must open a margin account with your brokerage firm. You will be charged interest on the borrowed funds as well as subject to several rules and regulations that govern shorting stock (for example, you cannot short a penny stock, and before you can begin shorting a stock, the last trade must be an uptick or zero-plus tick.) After taking these factors into consideration, you will, hopefully, realize shorting stock is not a financially fattening activity in most cases and comes along with additional risks.