Investing · Stock Valuation · Lesson
Price-to-Earnings Ratio (P/E)
A free lesson on the price-to-earnings ratio — one of the most common stock-valuation tools used by everyday investors. Students learn the P/E formula, what a “high” or “low” P/E means, and why P/E is associated with growth stocks.
What Students Learn
Learning objectives
- What the price-to-earnings (P/E) ratio is — the most common simple way to value a company’s stock
- How to calculate P/E by dividing the company’s stock price by its earnings per share (EPS)
- How to interpret a P/E ratio — whether the multiple suggests the stock is expensive or cheap relative to peers or its own history
- Why growth stocks tend to have higher P/E ratios — investors expect future earnings to grow, justifying the higher multiple today
- The most important limitation: P/E cannot be used to value a company with no earnings (or with negative earnings)
- How P/E fits alongside other valuation tools in real-world investment decisions
P/E = Stock Price ÷ EPSWorked example: if Microsoft (MSFT) stock is $30 and EPS is $1.00, then P/E = $30 ÷ $1.00 = 30. Investors are paying 30 times the company’s current earnings for one share.
For Teachers
How to use this lesson
P/E ratio is where most students first encounter the idea that a stock’s price isn’t an opinion — it has to be compared to something. Open by asking whether $30 is a “good price” for a share of stock. Students will probably say it depends on the company. Use that intuition to introduce the idea that a $30 stock with $1 of earnings (P/E = 30) is being valued very differently from a $30 stock with $5 of earnings (P/E = 6) — even though the dollar price is identical.
Discussion: Why might investors willingly pay 30 times earnings for one company but only 6 times earnings for another? This is the entry point for talking about growth expectations, business stability, and the difference between price and value. Modern examples: a high-growth tech stock vs. a mature utility company. Both might be legitimately good investments — just for different reasons.
The lesson’s most important honest caveat: P/E ratios cannot be calculated for companies with no earnings (or negative earnings — you can’t divide by zero or get a meaningful negative P/E). For those companies, investors use other valuation techniques. This is a good moment to introduce the broader topic of stock valuation methods (see related: Stock Valuation lesson). Best taught after students can read a stock table and know how to find both price and EPS.
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