What You'll Learn

Why Most Investors Misuse the P/E Ratio

I've been studying Warren Buffett's letters for over a decade, and the biggest mistake I see is people treating P/E ratio like a simple scoreboard. They think low P/E = buy, high P/E = avoid. But Buffett himself has said, “It's far better to buy a wonderful company at a fair price than a fair company at a wonderful price.”

The P/E ratio is just a starting point. What really matters is the quality of earnings and how sustainable they are. I remember analyzing a small manufacturing company with a P/E of 6. Looked cheap on the surface. But digging deeper, I found its earnings were declining, debt was piling up, and the moat was nonexistent. That's a value trap—and Buffett would never touch it.

Buffett doesn't look at P/E in isolation. He combines it with his famous owner earnings concept, which adjusts for maintenance capex and working capital needs. He then compares that to the purchase price to get a real yield. This is where the magic begins.

Buffett's P/E Philosophy: Earnings + Moat + Margin of Safety

Earnings Quality Comes First

Buffett favors companies with consistent, predictable earnings. He once said, “I look for businesses with a durable competitive advantage.” A low P/E is meaningless if earnings are erratic. Take a utility company: steady earnings, regulated environment—that's a perfect candidate for a Buffett-style P/E analysis. In contrast, a cyclical miner with a P/E of 5 might look tempting, but when commodity prices drop, those earnings can vanish. I personally avoid anything with volatile earnings unless I deeply understand the cycle.

The Moat Factor

A company's competitive advantage—its moat—determines how long it can sustain high returns. Buffett's favorite metric is return on equity (ROE) over many years. If ROE is consistently above 15% and the business has pricing power, then even a P/E of 20 might be reasonable. I once evaluated a premium spirits brand with a P/E of 25. Most analysts said it was overvalued, but the brand had pricing power, zero debt, and high repeat purchases. That's exactly the kind of moat Buffett loves.

Margin of Safety: The Buffett Rule

Buffett insists on buying with a margin of safety. That means the purchase price should be well below your calculated intrinsic value. For P/E, this often translates to a P/E ratio that is lower than the company's sustainable growth rate. For example, if a business can grow earnings at 10% annually, a P/E of 10 or less provides a nice buffer. I always calculate a range of intrinsic values using conservative growth assumptions, then only buy if the current P/E is below the lower bound.

How to Apply the Buffett P/E Method Step by Step

Here’s a practical framework I use (and you can too):

  1. Screen for low P/E: Start with a list of stocks with P/E below the industry average. But remember—that's just a filter, not a buy signal.
  2. Check earnings stability: Look at 10 years of earnings per share. If earnings grew consistently (even during recessions), move forward. If they fluctuated wildly, skip the stock.
  3. Assess the moat: What gives this company a sustainable advantage? Brand? Patents? Low-cost production? Network effects? If you can't explain it in one sentence, the moat is weak.
  4. Calculate owner earnings: Start with net income, add back depreciation, subtract maintenance capex. Divide by shares outstanding to get owner earnings per share. Use this instead of reported EPS.
  5. Determine a fair P/E: For a consistent grower, a P/E of 15 is reasonable. For a fast grower (12%+), maybe 20. For a no-grower, no more than 10. Adjust based on moat strength.
  6. Apply margin of safety: Multiply owner earnings per share by your fair P/E to get a fair price. Then demand at least a 20% discount. That's your buy zone.

I've used this process for years. It saved me from buying a well-known retailer with a P/E of 8 that later went bankrupt. The earnings seemed fine, but the moat was eroding due to online competition. The lesson: always verify the moat firsthand.

Real Cases: Coca-Cola, Apple, and Washington Post

Coca-Cola (1988)

When Buffett started buying Coca-Cola in 1988, the P/E was around 14. Not dirt cheap, but he saw the global expansion potential and the brand's pricing power. He calculated future cash flows and concluded that 14 was a steal. Over the next decade, earnings grew at 15% annually, and the P/E expanded to over 30. That's the double win: earnings growth plus multiple expansion.

Apple (2016 onward)

Buffett began purchasing Apple in 2016 when its P/E was about 10. Critics said it was a mature tech company with slowing growth. But Buffett recognized the ecosystem's stickiness and the massive cash flows. Apple's owner earnings were far higher than reported net income due to low capex needs. He bought more as the P/E rose, eventually paying around 15 times earnings. Today, Apple is Berkshire's largest holding. The key takeaway: a moderate P/E on a high-quality business is better than a low P/E on a mediocre one.

Washington Post (1973)

In the early 1970s, the Washington Post had a P/E of about 10. The market was depressed, but the Post had a local monopoly and strong brand. Buffett bought a large stake. Within a few years, earnings rebounded and the P/E nearly doubled. The margin of safety was huge—he bought when everyone else was scared.

These cases illustrate a consistent pattern: Buffett buys when the P/E is low relative to the company's future earning power and moat, not just low relative to the market.

Common Mistakes Investors Make

  • Ignoring debt: A low P/E can be misleading if the company has massive debt. Buffett prefers companies with little or no debt. I always check the debt-to-equity ratio and free cash flow.
  • Focusing on trailing P/E only: Forward P/E matters more. Buffet looks at the next 5–10 years of earnings potential. I once bought a stock with a trailing P/E of 8, but earnings were about to collapse due to a patent expiration. That was painful.
  • Confusing low P/E with value: As mentioned, value traps are real. The P/E must be supported by sustainable earnings and a strong moat.
  • Neglecting growth: A P/E of 20 with 15% growth is cheaper than a P/E of 10 with 2% growth. Buffett's partner Charlie Munger says, “Over the long term, it's hard for a stock to earn much more than the underlying business.” So low growth caps your return.

Your Questions Answered

Should I use trailing or forward P/E when emulating Buffett?
Stop overthinking this. Buffett uses a blend—trailing P/E gives you historical reality, forward P/E adds a lens. But he primarily relies on his own projection of future owner earnings. If the company has predictable earnings, forward P/E is okay; if not, stick with trailing and apply a margin of safety.
What P/E multiple does Buffett consider too high?
There's no fixed number, but from my analysis of his purchases, he rarely pays above 20 times owner earnings unless the business is extraordinary (like See's Candy in the 1970s). A general rule: if the P/E is above the company's sustainable growth rate, you're paying for optimism.
How do I find Buffett-style P/E opportunities today?
Start with sectors that have durable moats: consumer staples, utilities, and some tech (like software with recurring revenue). Screen for low debt, high ROE, and consistent earnings growth. Then apply the step-by-step method above. I personally scan the S&P 500 for stocks with P/E below 15 and ROE above 15%—that narrows the list quickly.