As an investor, understanding the factors that influence stock prices is crucial. Two primary drivers of stock prices are earnings growth and multiple expansion. To help illustrate these concepts, we will use the price-to-earnings (P/E) ratio, a popular valuation metric, as an example. By the end of this discussion, you will have a better grasp of how earnings growth or multiple expansion can affect stock prices.

The Price-to-Earnings (P/E) Ratio

The P/E ratio is a valuation metric that compares a company’s stock price to its earnings per share (EPS). It is calculated as follows:

P/E Ratio = Stock Price / Earnings per Share (EPS)

The P/E ratio is often used by investors to determine if a stock is overvalued or undervalued. A high P/E ratio may indicate that a stock is overvalued, while a low P/E ratio might suggest it is undervalued. Now, let’s explore how earnings growth and multiple expansion can impact the P/E ratio and, ultimately, stock prices.

Earnings Growth: Boosting the Bottom Line

When a company’s earnings grow, it means the company is making more money. Higher earnings can lead to a lower P/E ratio if the stock price remains constant, as the denominator (earnings per share) increases. However, if investors believe that the higher earnings are sustainable and indicative of a strong company, they may be willing to pay more for the stock, pushing the stock price higher. In this case, both the stock price and earnings have increased, and the P/E ratio may stay constant or increase slightly, depending on the relative growth rates of the stock price and earnings.

Multiple Expansion: Paying More for Future Growth

Multiple expansion occurs when the stock price increases without a corresponding increase in earnings. In this case, the P/E ratio will rise, as the numerator (stock price) increases while the denominator (earnings per share) stays the same. This can happen if investors become more optimistic about a company’s future growth prospects, the overall market conditions improve, or if interest rates decline, making stocks more attractive compared to other investments. When multiple expansion happens, investors are essentially willing to pay more for each dollar of earnings the company generates, expecting that the company’s future performance will justify the higher valuation.


Understanding the difference between earnings growth and multiple expansion, and their impact on stock prices, is essential for making informed investment decisions. The P/E ratio serves as a useful tool to help illustrate these concepts. By recognizing the factors that drive stock prices and the P/E ratio, investors can better assess the value of stocks and make more strategic investment choices.