Today has been a painful day if you are a short seller. Shares of Green Mountain Coffee (GMCR) and Tesla (TSLA) both had more than 25% of their free-floating shares sold short as of 4/15, and both are trading up more than 20% today. These are not just two isolated instances either. Taking a broader look at the overall market shows that stocks with high short interest have been fueling the recent rally.
In the chart below, we have broken out the S&P 1500 into deciles based on each stock's most recent (4/15) short interest as a percentage of float. We then calculated the average return of the stocks in each decile. Since April 15th, the average stock in the S&P 1500 is up 6.6%, but only three deciles have above average returns. What these three deciles have in common is that they are also the three deciles containing the most heavily shorted stocks. Meanwhile, the two worst performing deciles of stocks since 4/15 are the two that contain the least heavily shorted stocks. It is not uncommon for heavily shorted stocks to outperform when the market is in rally mode, but over the last month the short side has been especially painful.