P/E Ratio Calculator

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Calculate trailing and forward P/E ratios, earnings yield, and PEG ratio to assess stock valuation relative to earnings.

Trailing P/E—
Forward P/E—
Earnings Yield—
PEG Ratio—
20×
35×
0×
0×40×+
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P/E Ratio Formula

P/E = Stock Price / EPS

Trailing vs Forward P/E

  • Trailing P/E: Uses last 12 months of actual earnings. More reliable but backward-looking.
  • Forward P/E: Uses next 12 months analyst estimates. More relevant for growing companies — shows what the market is pricing in for the future.

If Forward P/E < Trailing P/E, the market expects earnings to grow. If Forward P/E > Trailing P/E, earnings are expected to shrink.

Earnings Yield

Earnings Yield = 1 / P/E × 100

Earnings yield is the inverse of P/E — it converts valuation into a return metric comparable to bond yields. A P/E of 20× = 5% earnings yield. Compare to 10-year Treasury yield to gauge relative attractiveness.

PEG Ratio (P/E to Growth)

PEG = P/E / Expected EPS Growth Rate (%)

Peter Lynch popularized PEG as a growth-adjusted valuation metric. PEG = 1 means the P/E equals the growth rate — "fairly valued." PEG < 1 suggests potential undervaluation; PEG > 2 suggests the stock is pricing in very high growth expectations.

S&P 500 Historical P/E Context

  • Long-run average: ~15–17×
  • Post-2010 average (low-rate era): ~20–25×
  • During recessions: often drops to 10–12×
  • Bubble peaks: 30–40×+

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What Is the P/E Ratio and How to Use It?

Complete guide to the price-to-earnings ratio: formula, trailing vs forward P/E, historical averages, and how investors use it for stock valuation.

Price-to-Earnings (P/E) Ratio

The P/E ratio measures how much investors pay per dollar of company earnings:

P/E = Stock Price / Earnings Per Share (EPS)

A P/E of 20 means investors pay $20 for every $1 of annual earnings.

Trailing vs Forward P/E

Trailing P/E uses the last 12 months of actual, reported EPS. It's backward-looking but based on real numbers.

Forward P/E uses next 12 months analyst EPS estimates. More relevant for valuing growing companies — it prices in expectations rather than history.

When forward P/E < trailing P/E, the market expects earnings growth. When forward P/E > trailing P/E, earnings are expected to shrink.

Historical P/E Benchmarks

Period / Condition Average P/E
S&P 500 long-run average 15–17×
Post-2010 (low-rate era) 20–25×
Recession troughs 10–12×
Dot-com bubble peak 40–50×+

P/E Limitations

  • Cyclical companies: P/E is misleading at earnings peaks; use normalized earnings
  • Negative EPS: P/E is undefined for loss-making companies
  • Different industries: Software companies naturally trade at higher P/E than utilities
  • Accounting choices: Earnings can be manipulated; cash flow multiples are more robust

Use the P/E Ratio Calculator to compute both trailing and forward P/E.

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PEG Ratio vs P/E Ratio: Which Is Better for Valuation?

How the PEG ratio improves on P/E by adjusting for growth rate — when to use each and what PEG values signal about valuation.

The Problem With P/E Alone

A P/E of 30× looks expensive for a slow-growth utility but cheap for a software company growing earnings at 40% per year. P/E ignores growth.

The PEG Ratio

Peter Lynch popularized the PEG ratio as a growth-adjusted valuation metric:

PEG = P/E Ratio / Expected EPS Growth Rate (%)

PEG removes the growth bias by normalizing P/E against growth expectations.

PEG Interpretation

PEG Signal
< 1.0 Potentially undervalued relative to growth
= 1.0 "Fairly priced" — paying exactly for growth
1–2 Moderate premium for growth
> 2 Expensive relative to growth expectations

Lynch's rule of thumb: A stock is attractively priced when PEG < 1. This heuristic works best for mid-cap growth companies; it's less reliable for mature, low-growth businesses.

PEG Limitations

  • Growth estimates are uncertain — a missed earnings estimate changes PEG dramatically
  • Less meaningful for value stocks and dividend payers
  • Doesn't account for debt, margins, or capital intensity
  • Best used as a screening tool, not a standalone buy/sell signal

Earnings Yield: Another P/E Derivative

Earnings yield (1 ÷ P/E × 100) converts valuation into a return metric. Compare it against 10-year Treasury yields — when earnings yield is close to or below bond yields, equities look less attractive on a risk-adjusted basis.

Use the P/E Ratio Calculator to compute trailing P/E, forward P/E, earnings yield, and PEG in one step.

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