Price/Earnings-to-Growth Ratio (PEG)

What It Is:

The PEG ratio is a derivative of the P/E ratio that takes into account future growth in earnings. 

How It Works/Example:

The formula for the PEG ratio is:

PEG Ratio = Price-to-Earnings (P/E) Ratio / Annual Earnings Per Share Growth

The PEG ratio uses the basic format of the P/E ratio for a numerator and then divides by the potential growth for the stock. The two ratios may seem to be very similar but you can see the obvious difference with a calculation.

Let us take Company XYZ stock. Say XYZ is currently trading with a P/E ratio of 30. Typically, this would be considered an "expensive" stock. But let's also assume analysts forecast growth in earnings per share of +40% for the next year.
In this case, XYZ's PEG ratio would be:

PEG Ratio = 30 (P/E ratio) / +40% (earnings growth) = 0.75

A rule of thumb is that any PEG ratio below 1.0 is considered to be a good value. So even though XYZ is highly valued based on the P/E ratio, the PEG ratio says that it is undervalued relative to its growth potential.

Why It Matters:

The PEG ratio acts as a measure of value that takes into account future growth. Using this metric, investors can gauge whether high-growth stocks may be undervalued, even if they don't appear so with the more common P/E ratio.