P/E ratio explained

Price-to-earnings: the most cited valuation metric — and its limits.

TL;DR

The P/E ratio is the share price divided by earnings per share. It tells you how many dollars investors are paying for each dollar of company profit.

The formula

P/E = Share price ÷ Earnings per share (EPS). Trailing P/E uses the last 12 months of earnings. Forward P/E uses the next 12 months of forecasts.

What the number means

A lower P/E generally means a cheaper stock relative to its earnings. A higher P/E means investors are paying up — usually because they expect rapid growth ahead. Industry context matters: a software company can trade at 40x while a bank trades at 8x and both can be reasonable.

→P/E under 15 — often value territory
→P/E 15–25 — typical for stable, profitable companies
→P/E 25–40 — growth expectations baked in
→P/E over 40 — high growth, high disappointment risk

Trailing vs forward P/E

Trailing P/E uses actual reported earnings — backward-looking but trustworthy. Forward P/E uses analyst estimates — forward-looking but only as good as the forecast.

Worked example

Apple (AAPL) worked example

AAPL trades at $230 with trailing 12-month EPS of $6.50.

1Share price$230
2Trailing EPS$6.50
3Trailing P/E$230 ÷ $6.50 = 35.4
4Forward EPS estimate$7.40
5Forward P/E$230 ÷ $7.40 = 31.1

Takeaway

AAPL trades at ~35x trailing earnings, ~31x forward. Investors are paying up for expected EPS growth.

Common mistakes

What to avoid

!Comparing P/Es across very different sectors — tech routinely trades higher than utilities
!Using P/E for unprofitable companies — the ratio is meaningless or negative
!Confusing trailing P/E with forward P/E — they can diverge widely during earnings inflections
!Treating a low P/E as automatically 'cheap' — sometimes it signals deteriorating fundamentals
!Ignoring debt — P/E ignores capital structure, EV/EBITDA accounts for it

Self-check

Test yourself

Q1A stock trades at $80 with EPS of $5. What's the P/E?+

$80 ÷ $5 = 16

Q2Why is P/E unreliable for unprofitable companies?+

EPS is negative or near zero, making the ratio meaningless or extreme.

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