Magic formula investing is an investment technique outlined by Joel Greenblatt that uses the principles of value investing.

Methodology

Greenblatt (b. 1957), an American professional asset manager since the 1980s, suggests purchasing 30 "good companies": cheap stocks with a high earnings yield and a high return on capital. He describes this as a simplified version of the strategy employed by Warren Buffett and Charlie Munger of Berkshire Hathaway. He touts the success of his magic formula in his book 'The Little Book that Beats the Market' (ISBN 0-471-73306-7 published 2005, revised 2010), stating it averaged a 17-year annual return of 30.8%. He wrote the book for a non-technical reader (his teenaged children were the target audience), but an appendix includes more advanced explanations and data for readers with relevant experience or education. Greenblatt's system analyzed the largest companies trading on the American stock market, ranked by the largest 1,000, 2,500 or 3,000, for a 17 year period before the book's 2005 publication. Smaller companies, $50 million or under, were avoided because they tend to have fewer shares in circulation and large purchases can cause sharp changes in share prices. Greenblatt did not test this hypothesis on international stock markets due to difficulties comparing international and American data, but believed it would apply globally. He also stressed the formula will not necessarily be successful with any specific stock, but will be successful for a group of stocks as a unit or block. He goes on to assigning numerical rankings, based on each company's earnings yield and return on capital: From here, Greenblatt recommends selecting 20 to 30 of the better-ranked companies, selling them at predetermined intervals and replacing with new stocks that fit the formula. Greenblatt's analysis found when applied to the largest 1,000 stocks the formula underperformed the market (defined as the S&P 500) for an average of five months out of each year. On an annual basis, the formula outperformed the market three out of four years but underperformed about 16% of two-year periods and 5% of three-year periods. Greenblatt asserts the formula out-performed market averages 100% of the time for any period longer than three years and worked best over three to five years or more. Results were even better and with lower risk when the formula was applied to larger pools of stocks like the largest 3,000 companies. The formula can thus be a contrarian investing strategy, focused sometimes on staying committed to stocks that might be temporarily unattractive or with sub-par performance. In an afterword to the 2010 edition, Greenblatt admitted three possible flaws to the formula. (1) The formula can underperform for up to several years which many investors will find discouraging. (2) Some amateurs found it cumbersome to track buying and selling times for stocks. (3) Beating the market does not necessarily imply making money (e.g. if the market loses 40% one year, following the formula might result in a 38% loss, which Greenblatt describes as "small consolation".)

Formula

Analysis around the world

A number of studies have found merit in Greenblatt's "magic investing formula" in various markets around the world. However, the studies have also often noted increased volatility, short-term underperformance and other potential risks.