Understanding P/E Ratio: A Beginner Guide
P/E ratio is the most-cited stock metric. Here is what it tells you, what it misses, and how to use it without getting tricked.
Don't have time? Here's what you need to know:
- 1P/E ratio = stock price divided by earnings per share; the S&P 500 average is about 16-17
- 2High P/E can mean expensive or high-growth; low P/E can mean cheap or declining earnings
- 3Compare P/E within the same sector, not across different industries
- 4For long-term ETF investors buying monthly, P/E is context — not a timing signal
P/E Ratio in 30 Seconds
The price-to-earnings ratio divides a stock's price by its annual earnings per share. If a stock trades at $100 and earns $5 per share, its P/E is 20. That means investors are paying $20 for every $1 of current annual earnings. The S&P 500's historical average P/E is about 16-17. As of 2024, it trades around 22-25, above the long-term average.
A high P/E (above 25) usually means investors expect the company to grow earnings quickly. Amazon traded at a P/E above 100 for years because the market expected massive future profit growth — and was right. A low P/E (below 12) can mean the company is cheap, or that the market expects earnings to decline. Low P/E is not automatically a bargain.
How to Use P/E (and How Not To)
Compare P/E ratios within the same sector or asset class — not across them. A tech company at P/E 30 might be cheap relative to other tech stocks. A utility at P/E 30 would be extremely expensive. Different industries have different normal ranges. The S&P 500's P/E also varies by market cycle: it was 44 at the 2000 dot-com peak and 10 at the 2009 bottom.
For ETF investors, the P/E of the overall market is more relevant than individual stocks. A high market P/E suggests future returns may be lower than the historical 10% average. A low market P/E suggests returns may be higher. But this is a weak signal — market timing based on P/E has a poor track record.
| P/E Range | What It Often Means | Historical Context |
|---|---|---|
| Under 12 | Cheap or declining earnings | S&P 500 bottoms (2009, 2011) |
| 12-18 | Fair value for market average | Long-term S&P 500 average is ~16 |
| 18-25 | Moderate optimism | Most of the 2010s-2020s bull market |
| Above 25 | High expectations for growth | Dot-com bubble peak was P/E 44 |
Why ETF Investors Should Not Obsess Over P/E
If you are buying VTI or VOO monthly for 20+ years, the current market P/E barely matters. You will buy shares at high P/E ratios, low P/E ratios, and everything in between. Dollar-cost averaging smooths out the impact of valuation on your purchase prices. The investor who bought VOO monthly from 2000 to 2020 — including the dot-com peak (P/E 44) and the 2008 bottom (P/E 10) — earned excellent returns.
P/E is useful for context and education, not for timing decisions. Knowing that the market is expensive (high P/E) or cheap (low P/E) helps you set realistic return expectations, but it should not change your investment behavior.
Tip: If you want to check the S&P 500's current P/E ratio, search for 'Shiller CAPE ratio.' The cyclically adjusted P/E smooths earnings over 10 years and gives a better picture than trailing 12-month P/E.
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Frequently Asked Questions
Is a P/E of 25 too high to invest?
Not necessarily. The S&P 500 has traded at P/E 20-25 for most of the past decade and delivered strong returns. High P/E relative to history might mean lower future returns, but it does not mean losses. Investors who waited for a 'normal' P/E of 16 in 2015 missed years of gains.
Why do some ETFs have no P/E ratio listed?
Bond ETFs do not have P/E ratios because bonds pay interest, not earnings. Some sector ETFs with many money-losing companies (like biotech) may show unusually high or negative P/E ratios. P/E is a stock valuation metric and does not apply to all investment types.
What is a forward P/E vs trailing P/E?
Trailing P/E uses actual earnings from the past 12 months. Forward P/E uses analyst estimates for the next 12 months. Forward P/E is usually lower because analysts expect earnings to grow. Both are useful — trailing P/E is more reliable (actual data), forward P/E reflects current expectations.
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Alex Harrington
CFA Level II Candidate, Finance & Economics
Alex Harrington is an independent ETF researcher and personal finance writer with over 8 years of experience analyzing exchange-traded funds. A CFA Level II candidate with a background in economics, Alex has reviewed 800+ ETFs and helped thousands of beginners build their first investment portfolios through clear, jargon-free education.
This content is for educational purposes only and does not constitute financial advice. Past performance does not guarantee future results. Consult a licensed financial advisor before making investment decisions.