Assessing Stock Valuation with the PEG Ratio Calculator
The PEG Ratio Calculator helps investors evaluate whether a stock's price is justified by its expected earnings growth. By entering the stock price, earnings per share, and anticipated growth rate, it computes the PEG ratio and related valuation metrics.
For instance, a stock trading at $150 with $5 EPS and 15% growth yields a PEG of 2.00, indicating it may be overvalued relative to its growth prospects.
Why the PEG Ratio Matters in Investment Decisions
The PEG ratio provides more nuanced valuation than the P/E ratio alone. While P/E shows how much investors pay for current earnings, PEG factors in future growth trajectory. A low PEG signals that a company may be undervalued relative to its growth potential, guiding investors to opportunities where the market has not fully priced in future earnings expansion.
The Formula Behind the PEG Ratio
The PEG ratio is derived from the P/E ratio, incorporating the expected earnings growth rate.
First, calculate the P/E Ratio:
P/E Ratio = Stock Price / Earnings Per Share (EPS)
Then, calculate the PEG Ratio:
PEG Ratio = P/E Ratio / Earnings Growth Rate (%)
Additional metrics:
PEG=1 Fair Value = EPS × Earnings Growth Rate
Earnings Yield = (EPS / Stock Price) × 100
Breakeven Growth Rate = P/E Ratio (the growth % needed for PEG = 1)
Valuing a Growth Stock: A Worked Example
Let's analyze a technology stock with the following data:
- Stock Price: $150
- Earnings Per Share (EPS): $5
- Earnings Growth Rate: 15%
Step-by-step calculations:
- P/E Ratio: $150 / $5 = 30.00
- PEG Ratio: 30 / 15 = 2.00
- PEG=1 Fair Value: $5 x 15 = $75.00
- Price vs. Fair Value: ($150 - $75) / $75 x 100 = 100.0% above fair value
- Earnings Yield: ($5 / $150) x 100 = 3.33%
- Breakeven Growth Rate: 30.0% (equals the P/E ratio)
A PEG of 2.00 means the stock trades at twice its earnings growth rate, suggesting overvaluation if PEG=1 is considered fair value.
The stock would need 30% annual growth to justify its current price.
Advanced Valuation Metrics in Investment Analysis
The PEG ratio stands as a vital advanced valuation metric, particularly for growth-oriented companies. A PEG of 1.0 is widely considered a benchmark for fair value, while seasoned investors often look for PEGs below 1.0, indicating potential undervaluation relative to growth prospects.
However, the PEG has limitations: it assumes linear growth, does not account for risk or capital structure, and requires accurate growth estimates. In 2026, with varying market conditions across sectors, combining PEG with other metrics like EV/EBITDA, free cash flow yield, and debt-to-equity provides a more complete valuation picture.
The Genesis of the PEG Ratio in Modern Finance
The PEG ratio is most famously associated with Peter Lynch, the renowned manager of the Fidelity Magellan Fund, who popularized its use in his influential book "One Up On Wall Street" (1989). Lynch advocated buying stocks where the P/E ratio was roughly equal to the earnings growth rate — essentially a PEG of 1.0.
He found this a simple yet powerful way to identify growth companies that were still reasonably priced, distinguishing them from those whose high P/E ratios were not justified by their future prospects. The concept remains a fundamental tool for value and growth investors in 2026.