The PEG ratio (price-to-earnings-to-growth ratio) is an extension of the P/E ratio. When considering the company's growth rate, it is used to determine whether a stock is overvalued, undervalued, or fairly valued.
The P/E ratio calculates the stock's price-per-share by the company's earnings-per-share (EPS). For example, if a company's stock is trading at $30 per share and the company's EPS is $2.50, the company's P/E ratio would be 30 divided by 2.50, or 12. A P/E ratio of 12 means that the company's stock price is trading at 12 times the company's earnings.
The PEG ratio calculates the stock's price-per-share by the company's EPS growth rate. For example, if a company's stock is trading at $30 per share and the company's EPS is expected to grow at a rate of 20% per year, the company's PEG ratio would be 30 divided by 20, or 1.5. A PEG ratio of 1.5 means that the company's stock price is trading at 1.5 times the company's EPS growth rate.