Price-to-Earnings Growth Ratio

The PEG ratio was popularized by Peter Lynch, the former portfolio manager of Fidelity's Magellan Fund, who argued that paying a high P/E multiple for a high-growth business was not necessarily expensive if earnings were growing fast enough to justify the multiple. The formula divides the trailing or forward P/E ratio by the expected annual earnings growth rate expressed as a percentage. A company trading at 30 times earnings with a 30% expected growth rate would carry a PEG of 1.0, while the same multiple applied to a 15% grower would yield a PEG of 2.0.

The PEG ratio has intuitive appeal because it collapses the trade-off between price and growth into a single number, allowing investors to compare companies growing at very different rates on a more apples-to-apples basis. It has been widely applied to U.S. technology and consumer growth companies where raw P/E multiples can appear prohibitively high without the growth context.

The metric has meaningful limitations. The denominator — expected earnings growth — is an estimate subject to significant error, particularly for companies with volatile or lumpy earnings streams. Using different time horizons for the growth rate (one-year versus five-year, trailing versus forward) produces very different PEG values for the same company. Earnings growth estimates for high-multiple companies are also subject to optimism bias in sell-side research, which can make PEG ratios look more reasonable than the underlying fundamentals warrant.

For mature, low-growth businesses — utilities, consumer staples, and many financials — the PEG ratio is less commonly used as a primary valuation tool, because the growth rates involved are small and the relationship between growth and fair value is more complex. In these sectors, yield-based metrics or asset-based approaches typically carry more analytical weight.