Price-to-Earnings Ratio (PE)
PE is a rearview mirror — it looks at the past, but you buy the future
📌 Concept Analysis
Price-to-Earnings (PE) = historical data; for reference only, not as a buy criterion.
When you drive, the rearview mirror tells you what’s behind you but can’t show you the road ahead. PE is that rearview mirror — it reflects the company’s past earnings, while buying stocks means buying the company’s future cash flow. Driving while staring at the rearview mirror will inevitably lead to trouble.
💡 Core Understanding
1. PE is historical data and cannot be used alone as a criterion for buying or not buying.
PE reflects the company’s past earnings, while discounted future cash flow is where the company’s true value lies. A company with low PE doesn’t mean it’s cheap — General Motors’ PE was around 5x long-term, yet it had massive debt and eventually went bankrupt. A company with high PE doesn’t mean it’s expensive — if you’re confident about its high growth, high PE is acceptable.
2. Duan Yongping uses not the reported PE but “PE relative to future long-term real profits.”
The PE he refers to is your own judgment of the company’s future long-term earning power, not the number on financial reports. These are fundamentally different things. The core of rough estimation is: what multiple of PE you’re willing to pay depends entirely on your own judgment of the company’s future and your own capital’s opportunity cost — it has nothing to do with the market.
3. 12x PE is a rough reference line, but not an iron rule.
Duan Yongping mentioned that what PE multiple is appropriate relates to average long-term interest rates — around 12x long-term PE should be fine. But he emphasized this is only a rough reference, not a standard answer — he himself said “I actually don’t know what PE to give.” What truly matters is your judgment of the company’s intrinsic value, not applying a formulaic multiple.
4. Companies with extremely low PE are often problematic companies.
This contradicts many people’s intuition — many assume low PE means cheap, but behind low PE often lie risks the market has already seen. Low PE companies outside your circle of competence — don’t touch.
🛠 How to Practice
The right way to use PE:
- Use PE as reference, not as criterion. When you see a company’s PE, first ask yourself: does this PE correspond to past or future earnings? If the company is in a high-growth phase, current high PE doesn’t mean expensive; if earnings are declining, low PE doesn’t mean cheap.
- Recalculate PE using “future long-term real profits.” Don’t use the reported PE directly — estimate the company’s average annual profit over the next 5–10 years, then divide current market cap by this number to get your own “real PE.”
- Combine with opportunity cost. What multiple of PE you’re willing to pay depends on what return your capital can get elsewhere. If your capital can earn a 20x PE return elsewhere, then a stock at 60x PE is unreasonable.
❓ Selected Q&A
Q: Do you care about the PE ratio of stocks you invest in?
A: I look at it but don’t focus on it. PE is historical data; we’re buying future cash flows. So unless you can see the future from history, it’s meaningless. Compared to PE, I use E/E more to evaluate an enterprise.
Source: Duan Yongping Investment Q&A (Investment Logic), 2010-06-01
Q: Even for good companies, beyond what PE multiple should one not buy?
A: Having such thoughts shows you still don’t understand companies. For example, when Netease was still losing money…
Source: Duan Yongping Investment Q&A (Investment Logic), 2013-03-26
Q: What PE multiple is appropriate?
A: What PE multiple is appropriate relates to average long-term interest rates — 12x long-term PE should be fine. I generally use around this number too.
Source: Duan Yongping Investment Q&A (Investment Logic), 2011-01-05
⚠️ Common Pitfalls
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❌ “Low PE means cheap and worth buying” — Correct answer: Duan Yongping said “Generally speaking, companies with very low PE are likely problematic. Unless you understand them well, better not touch.” GM’s PE was around 5x long-term, yet it eventually went bankrupt. (Source: Investment Logic, 2011-06-17)
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❌ “High PE means expensive and shouldn’t be bought” — Correct answer: “For high-growth enterprises, somewhat higher PE is acceptable, as long as you’re certain of their high growth. If you understand discounted future cash flow, this question won’t arise.”(Source: Investment Logic, 2011-04-05)
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❌ “Use reported PE to judge valuation” — Correct answer: The PE Duan Yongping refers to means “PE relative to future long-term real profits, not the ordinary PE on financial reports.” (Source: Investment Logic, 2011-10-01)
💬 Original Quotes
“PE is historical data; we’re buying future cash flows.” (Source: Duan Yongping Investment Q&A (Investment Logic), 2010-06-01)
“The P/E ratio is a rearview mirror and cannot serve as a criterion for whether to invest. What matters is future earning power — if you don’t understand it, no matter how low, don’t touch.” (Source: Duan Yongping Investment Q&A (Investment Logic), 2019-09-16)
“Never be misled by PE because it’s historical data and may not indicate the future. The PE I generally refer to is PE relative to future long-term real profits, not the ordinary PE on financial reports. What PE you’re willing to pay depends entirely on your own ability or the opportunity cost of your capital — it actually has nothing to do with the market.” (Source: Duan Yongping Investment Q&A (Investment Logic), 2011-10-01)
“Generally speaking, companies with very low PE are likely problematic. Unless you understand them well, better not touch.” (Source: Duan Yongping Investment Q&A (Investment Logic), 2011-06-17)
🔗 Related Nodes
Upstream Concepts (prerequisites for understanding this concept): 未来现金流折现 · 内在价值 · 毛估估
Downstream Concepts (conclusions derived from this): 机会成本 · 安全边际 · 买入逻辑
市盈率（PE）
PE 是倒后镜，看的是过去，买的是未来
📌 概念解析
市盈率（PE）= 历史数据，只能参考，不能作为买入标准。
你开车时，倒后镜能告诉你身后有什么，但不能告诉你前方的路。PE 就是这面倒后镜——它反映的是公司过去的盈利，而你买股票买的是公司未来的现金流。看着倒后镜开车，迟早出事。
💡 核心理解
1. PE 是历史数据，不能单独作为买入或不买的标准。
PE 反映的是公司过去的盈利，而未来现金流折现才是公司真正的价值所在。一家公司 PE 很低，不代表便宜——通用汽车（GM）PE 长期在 5 倍左右，但债务极高，最终破产。一家公司 PE 很高，也不代表贵——如果你能确定它的高成长，高 PE 是可以接受的。
2. 段永平用的不是财报上的 PE，而是”相对于未来长期实际利润的 PE”。
他说的 PE，指的是你自己对公司未来长期盈利能力的判断，而不是财报上那个数字。这两件事有本质区别。毛估估的核心就是：你愿意给多少倍 PE，完全取决于你自己对公司未来的判断，以及你自己资金的机会成本，和市场无关。
3. 12 倍 PE 是一个粗略参照线，但不是铁律。
段永平提到，多少倍 PE 和平均长期利息有关，12 倍长期 PE 大概可以了。但他同时强调，这只是一个粗略参照，不是标准答案——他自己也说”我其实不知道该给多少 PE”。真正重要的是你对公司内在价值的判断，而不是套用一个倍数。
4. PE 极低的公司，往往是有问题的公司。
这和很多人的直觉相反——很多人以为 PE 低就是便宜，但低 PE 背后往往藏着市场已经看到的风险。能力圈之外的低 PE 公司，不要碰。
🛠 如何实践
用 PE 的正确姿势：
- 把 PE 当参考，不当标准。 看到一家公司的 PE，先问自己：这个 PE 对应的是过去的盈利，还是未来的盈利？如果公司正处于高速成长期，当前 PE 高不代表贵；如果公司盈利在下滑，低 PE 也不代表便宜。
- 用”未来长期实际利润”重新算 PE。 不要直接用财报上的 PE，而是估算公司未来 5-10 年的平均年利润，再用当前市值除以这个数，得到你自己的”真实 PE”。
- 结合机会成本判断。 你愿意给多少倍 PE，取决于你的资金在其他地方能拿到多少回报。如果你的资金在别处能拿到 20 倍 PE 的回报，那 60 倍 PE 的股票就是不合理的。
❓ 精选问答
问：你对所投资的公司股票市盈率看重吗？
答：看但不看重。PE 是历史数据，我们买的是未来的现金流。所以除非你能从历史中看到未来，否则没意义。相对于 PE，我会更多用 E/E 来衡量一个企业。
来源：段永平投资问答录(投资逻辑篇)，2010-06-01
问：即使是好公司，一般市盈率超过多少倍不应该买入呢？
答：有这种想法就说明你还不懂公司。比如网易当年还在亏钱的时候……
来源：段永平投资问答录(投资逻辑篇)，2013-03-26
问：多少倍 PE 合适？
答：多少倍 PE 和平均长期利息有关，12 倍长期 PE 应该可以了，我一般大概也用这个数左右。
来源：段永平投资问答录(投资逻辑篇)，2011-01-05
⚠️ 常见误区
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❌ “PE 低就是便宜，值得买” — 正解：段永平说”一般来讲，PE 很低的公司很可能是有问题的公司，除非你了解，否则最好别碰。“GM 的 PE 长期在 5 倍左右，最终还是破产了。（来源：投资逻辑篇，2011-06-17）
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❌ “PE 高就是贵，不能买” — 正解：“对高成长的企业来说，PE 高些是可以接受的，只要你能确定他的高成长就行。如果你明白未来现金流折现的概念的话，就不会有这个问题。“（来源：投资逻辑篇，2011-04-05）
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❌ “用财报上的 PE 来判断估值” — 正解：段永平说的 PE 指的是”相对于未来长期实际利润的 PE，不是一般财报上的那个 PE”。（来源：投资逻辑篇，2011-10-01）
💬 原文金句
“PE 是历史数据，我们买的是未来的现金流。“（来源：段永平投资问答录(投资逻辑篇)，2010-06-01）
“市盈率是倒后镜，不能作为能不能投的标准。关键是未来的盈利能力，看不懂的再低也别碰。“（来源：段永平投资问答录(投资逻辑篇)，2019-09-16）
“千万不要被 PE 误导，因为 PE 是个历史数据，未必能说明未来。我说的 PE 一般指的是相对于未来长期实际利润的 PE，不是一般财报上的那个 PE。你愿意给多少 PE 完全取决于你自己的能力或者说你自己的资金的机会成本，其实和市场无关。“（来源：段永平投资问答录(投资逻辑篇)，2011-10-01）
“一般来讲，PE 很低的公司很可能是有问题的公司，除非你了解，否则最好别碰。“（来源：段永平投资问答录(投资逻辑篇)，2011-06-17）
🔗 关联节点
上游概念（理解这个概念的前提）： 未来现金流折现 · 内在价值 · 毛估估