Price/Earnings-to-Growth (PEG) Ratio: What It Is and the Formula

What Is the Price/Earnings-to-Growth (PEG) Ratio?

The price/earnings to growth ratio (PEG ratio) is a stock's price-to-earnings (P/E) ratio divided by the growth rate of its earnings for a specified time period.

The PEG ratio is used to determine a stock's value while also factoring in the company's expected earnings growth, and it is thought to provide a more complete picture than the more standard P/E ratio.

How to Calculate the PEG Ratio

$\begin{aligned} &\text{PEG Ratio}=\frac{\text{Price/EPS}}{\text{EPS Growth}}\\ &\textbf{where:}\\ &\text{EPS = The earnings per share}\\ \end{aligned}$​PEG Ratio=EPS GrowthPrice/EPS​where:EPS = The earnings per share​

To calculate the PEG ratio, an investor or analyst needs to either look up or calculate the P/E ratio of the company in question. The P/E ratio is calculated as the price per share of the company divided by the earnings per share (EPS), or price per share / EPS.

Once the P/E is calculated, find the expected growth rate for the stock in question, using analyst estimates available on financial websites that follow the stock. Plug the figures into the equation, and solve for the PEG ratio number.

Accuracy

As with any ratio, the accuracy of the PEG ratio depends on the inputs used. When considering a company's PEG ratio from a published source, it's important to find out which growth rate was used in the calculation. In an article from Morgan Stanley Wealth Management, for example, the PEG ratio is calculated using a P/E ratio based on current-year data and a five-year expected growth rate.

Using historical growth rates, for example, may provide an inaccurate PEG ratio if future growth rates are expected to deviate from a company's historical growth. The ratio can be calculated using one-year, three-year, or five-year expected growth rates, for example.

What Does the PEG Ratio Tell You?

While a low P/E ratio may make a stock look like a good buy, factoring in the company's growth rate to get the stock's PEG ratio may tell a different story. The lower the PEG ratio, the more the stock may be undervalued given its future earnings expectations. Adding a company's expected growth into the ratio helps to adjust the result for companies that may have a high growth rate and a high P/E ratio.

The degree to which a PEG ratio result indicates an over or underpriced stock varies by industry and by company type. As a broad rule of thumb, some investors feel that a PEG ratio below one is desirable.

According to well-known investor Peter Lynch, a company's P/E and expected growth should be equal, which denotes a fairly valued company and supports a PEG ratio of 1.0. When a company's PEG exceeds 1.0, it's considered overvalued while a stock with a PEG of less than 1.0 is considered undervalued.

Example of How to Use the PEG Ratio

The PEG ratio provides useful information to compare companies and see which stock might be the better choice for an investor's needs, as follows.

Assume the following data for two hypothetical companies, Company A and Company B:

Company A:

• Price per share = $46
• EPS this year = $2.09
• EPS last year = $1.74

Company B

• Price per share = $80
• EPS this year = $2.67
• EPS last year = $1.78

Given this information, the following data can be calculated for each company:

Company A

• P/E ratio = $46 / $2.09 = 22
• Earnings growth rate = ($2.09 / $1.74) - 1 = 20%
• PEG ratio = 22 / 20 = 1.1

Company B

• P/E ratio = $80 / $2.67 = 30
• Earnings growth rate = ($2.67 / $1.78) - 1 = 50%
• PEG ratio = 30 / 50 = 0.6

Many investors may look at Company A and find it more attractive since it has a lower P/E ratio among the two companies. But compared to Company B, it doesn't have a high enough growth rate to justify its current P/E. Company B is trading at a discount to its growth rate and investors purchasing it are paying less per unit of earnings growth. Based on its lower PEG, Company B may be relatively the better buy.

The Bottom Line

While the P/E ratio is more commonly used by investors, the PEG ratio improves upon the P/E by incorporating earnings growth estimates. This provides a fuller picture of a company's relative value in the market. However, because it relies on earnings estimates, having good estimates is key. A bad forecast or assumption, or naively projecting historical growth rates into the future, can produce unreliable PEG ratios.