Price-to-Earnings Ratio

The Price-to-Earnings (P/E) ratio is a widely used financial metric to evaluate the valuation of a company’s stock. It is a simple yet powerful tool that helps investors understand the relationship between a company’s stock price and its earnings per share. This essay will provide an overview of the P/E ratio, discuss its history, explain when and how it is used, and provide guidance on how to interpret its values.

History of the Price-to-Earnings Ratio

The P/E ratio has been used by investors for over a century to evaluate the attractiveness of a company’s stock. Benjamin Graham and David Dodd, widely regarded as the fathers of value investing, popularized the use of the P/E ratio in their seminal 1934 book, “Security Analysis.” Since then, the P/E ratio has become a staple in the financial analysis of public companies.

Calculation and Interpretation of the Price-to-Earnings Ratio

The P/E ratio is calculated by dividing the market price of a stock by its earnings per share (EPS). The formula for the P/E ratio is:

P/E Ratio = Stock Price / Earnings Per Share

A high P/E ratio indicates that investors are willing to pay a premium for a company’s stock relative to its earnings, implying that they expect strong future growth. Conversely, a low P/E ratio suggests that the stock is undervalued or that investors expect slower growth in the future.

It is important to note that the P/E ratio is a relative valuation metric, meaning that it should be used to compare companies within the same industry or sector. Comparing P/E ratios across different industries can lead to misleading conclusions, as different sectors have different growth prospects and risk profiles.

Determining if a Stock is Overpriced or Underpriced

To determine whether a stock is overpriced or underpriced based on its P/E ratio, investors can compare it to the average P/E ratio of other companies within the same industry. If a company’s P/E ratio is significantly higher than the industry average, it may be considered overpriced. Conversely, if the P/E ratio is significantly lower than the industry average, the stock may be considered undervalued.


Let’s assume that XYZ Company has a stock price of $50 and reported earnings per share of $2 for the most recent fiscal year. Using the formula mentioned earlier, we can calculate the P/E ratio as follows:

P/E Ratio = $50 / $2 = 25

Now, let’s assume that the average P/E ratio for the industry in which XYZ Company operates is 20. In this case, XYZ Company’s P/E ratio of 25 is higher than the industry average, suggesting that it may be overpriced compared to its peers.

Now let’s consider two well-known companies: Apple Inc. (AAPL) and Inc. (AMZN). In this example, we will use historical P/E ratios from September 2021.

  1. Apple Inc. (AAPL)
  • Market Price (as of September 2021): $154.30
  • Earnings per Share (EPS): $5.11
  • P/E Ratio: Market Price / EPS = $154.30 / $5.11 ≈ 30.20
  1. Inc. (AMZN)
  • Market Price (as of September 2021): $3,499.12
  • Earnings per Share (EPS): $52.56
  • P/E Ratio: Market Price / EPS = $3,499.12 / $52.56 ≈ 66.58

Comparing the P/E ratios of Apple Inc. and Inc., we can see that Apple’s P/E ratio of 30.20 is lower than Amazon’s P/E ratio of 66.58. Therefore, in this example, Apple Inc. has a low P/E ratio, and Inc. has a high P/E ratio. Keep in mind that a low P/E ratio doesn’t necessarily mean a company is undervalued or a better investment, as various factors should be considered when evaluating stocks.

Comparing P/E Ratios to Industry Standards

To ensure a more accurate analysis, it is crucial to compare a company’s P/E ratio to industry standards. This can be done by looking up the average P/E ratio for the industry or sector in which the company operates. Financial websites, such as Yahoo Finance, often provide industry averages for various valuation metrics, including the P/E ratio.

Other Considerations

While the P/E ratio is a useful tool, it should not be the sole basis for making investment decisions. It is important to consider other financial metrics, such as the Price-to-Sales (P/S) ratio and the Price-to-Book (P/B) ratio, as well as qualitative factors like the company’s management team, competitive advantages, and overall business strategy.


The Price-to-Earnings ratio is an essential tool for evaluating the valuation of a company’s stock. By comparing a company’s PE ratio to industry averages, investors can gain valuable insights into whether a stock is overpriced or underpriced. However, it is important to remember that the P/E ratio is just one of many financial metrics that should be considered when making investment decisions. By combining the P/E ratio with other quantitative and qualitative factors, investors can make more informed decisions and better assess the potential risks and rewards of their investments.