PEG ratio — Growth Stock Valuation

What is the PEG Ratio?

The PEG (Price/Earnings to Growth) ratio is calculated by dividing a company's P/E ratio by its earnings growth rate. While the P/E ratio shows "how many times the current earnings the stock price is," the PEG ratio combines this with "how quickly those earnings are growing." It's an attempt to express the intuition that fast-growing companies deserve a higher P/E ratio in a single number.

This concept was popularized by British investor Jim Slater and later widely recognized after Peter Lynch cited it in his books. Using only the P/E ratio can lead to comparing growth stocks and low-growth stocks with the same standard. The PEG ratio attempts to address this limitation by introducing the variable of growth rate. This article is for educational purposes, explaining the principles of the metric, and does not recommend buying specific stocks.

Calculation Method and Principle

The formula is PEG = P/E ratio ÷ Annual EPS Growth Rate (%). Here, only the percentage number for the growth rate is used. For example, if a share price is $100 and EPS is $5, the P/E ratio is 20x. If this company's annual earnings growth rate is expected to be 20%, the PEG ratio becomes 20 ÷ 20 = 1.0.

Even with the same P/E ratio of 20x, the PEG ratio can vary significantly with different growth rates. If the growth rate is 40%, the PEG ratio is 20 ÷ 40 = 0.5. If the growth rate is 10%, it's 20 ÷ 10 = 2.0. In essence, the PEG ratio numerically illustrates that "a high P/E ratio can appear inexpensive for a fast-growing company."

What you use for the growth rate significantly impacts the result. You can use historical earnings growth rates from the past few years, or future growth rates estimated by analysts. Using future estimates makes the metric sensitive to assumptions, so it's meaningful to apply the same growth rate criteria when comparing different stocks.

Interpretation Guidelines

Traditionally, a PEG ratio of 1.0 is considered a benchmark. If the PEG ratio is below 1, it suggests the P/E ratio is low relative to the growth rate, indicating it might be relatively undervalued. If it's above 1, it suggests the stock is trading at a higher price compared to its growth speed. Slater even suggested that a PEG ratio of 0.75 or lower indicates an attractive valuation.

However, 1.0 is not an absolute truth but an approximate guideline derived from experience. When interest rates are low, the present value of future earnings is higher, and it's common for the overall market's PEG ratio to exceed 1. Conversely, it tends to be lower when interest rates are high. Therefore, it's safer to interpret the PEG ratio by comparing it within the same industry or observing its changes over time, rather than relying on its absolute value.

Practical Application

The PEG ratio is useful for lining up growth stocks within the same industry. If you compare Company A with a P/E ratio of 30x and a growth rate of 30% (PEG 1.0) to Company B with a P/E ratio of 25x and a growth rate of 50% (PEG 0.5), Company B appears cheaper based on P/E alone, but the PEG ratio clarifies that difference even more. It helps reduce the mistake of assuming growth stocks are always expensive just by looking at their absolute P/E ratio.

In the Korean market, the PEG ratio is often discussed for growth sectors with significant earnings volatility, such as semiconductors, secondary batteries, and biotechnology. The same applies to fast-growing technology companies in the US market. However, in any market, it's reasonable to use the PEG ratio as a starting point for analysis, read alongside other metrics like the P/E ratio, operating margin, debt-to-equity ratio, and cash flow, rather than as a standalone conclusion.

Pitfalls and Limitations

The biggest weakness is that the result is entirely swayed by the growth rate assumption. If a growth rate of 30% yields a PEG ratio of 1.0, but the actual growth turns out to be only 15%, the PEG ratio doubles to 2.0 for the same stock price. High growth is not eternal and typically slows down over time, so projecting a single year's high growth rate directly into the future can lead to an overly optimistic metric.

The PEG ratio cannot be applied to companies with zero or negative growth rates, or those with negative EPS due to losses. Additionally, if EPS surges due to one-time gains or accounting changes, the growth rate can be inflated, making the PEG ratio appear unrealistically low. For cyclical industries, earnings fluctuate, making the growth rate itself unstable, which reduces the reliability of the PEG ratio.

For companies that pay high dividends, the basic PEG ratio, which only considers the growth rate, might appear unfavorable. In such cases, variations like PEGY, which adds the dividend yield to the denominator, are sometimes used. Regardless of the variation, the core principle remains the same: the PEG ratio is merely a convenient summary, and assumptions about future growth should not be trusted without verification.

Key Takeaways

In summary, the PEG ratio is a supplementary metric that adjusts the P/E ratio by the growth rate to gauge the price of growth stocks. While 1.0 serves as a rough benchmark, it should be interpreted flexibly based on the interest rate environment and industry characteristics, with more emphasis on peer comparisons than absolute values.

Before using it, it's good to check three things: first, whether the growth rate is historical performance or a future estimate; second, whether that high growth is sustainable; and third, whether the growth rate is distorted by losses, one-time gains, or cyclicality. The PEG ratio is a starting point for judgment, not a conclusion, and this article is educational material to aid in understanding the metric, not an investment recommendation.