The P/E ratio (Price-to-Earnings) is one of the financial indicators most used by investors to estimate the price of a share in relation to its profits. This analysis tool is used to determine whether a company is overvalued, undervalued or properly valued in financial markets. Understanding the calculation and interpretation of the p/e ratio is essential to making informed investment decisions.
What is the p/e ratio (Price Earnings Ratio)
Definition of the financial ratio
The P/E ratio, also known as Price Earnings Ratio (PRE), or multiple capitalisation of results, measures the relationship between the price of a share and the profit per share of a company. It indicates how many years of current profits are needed to recover the price paid for the share.
In simple terms, if the share is 15 per share, this means that investors agree to pay 15 times the annual profit per share to hold that share. This ratio allows financial analysts to quickly compare the valuation of different companies, even in various sectors.
Difference between historical PER and prospective PER
The market distinguishes two main types of p/e ratio according to the reference period of the profits used:
- Historical PER (trailing) : calculated with the actual profits of the last 12 months
- Forward-looking PER based on profit forecasts for the following year
The prospective RIP offers a forward-looking vision but remains subject to uncertainties in the forecast, while the historical RIP is based on real data but may not reflect the company's future prospects.
How to calculate p/e: formula and practical examples
Formula for calculating the ratio p/e
The formula of the p/e remains remarkably simple:
P/E = Price per share ÷ Profit per share (BPA)
Profit per share is calculated by dividing the company's net profit by the number of shares in circulation. This standardization enables companies of different sizes to be compared on a fair basis.
Examples of calculation with real enterprises
Take the example of a listed company whose share is traded at EUR 120 with a profit per share of EUR 8:
P/E = 120 € 8 € = 15
For a technology company valued 250 euros per share with a BPA of 5 euros:
P/E = 250 € 5 € = 50
These examples show how the p/e ratio varies significantly between sectors and types of enterprises.
Calculation of p/e for a stock portfolio
To calculate the P/E of a diversified portfolio, two methods are available to investors:
- Weighted average : multiply the P/E of each position by its weight in the portfolio
- Aggregate P/E : divide the total capitalization of the portfolio by the sum of the profits of all positions
The aggregate method generally provides a more accurate view of the overall valuation of the portfolio.
Interpretation and analysis of p/e ratio
What does high or low mean?
The interpretation of the p/e ratio depends largely on the context and expectations of the market:
| P/E level | General interpretation | Implications |
|---|---|---|
| Low P/E (5-10) | Potentially undervalued action | Investment opportunity or sector in difficulty |
| Moderate P/E (10-20) | Balanced valuation | Stable and predictable growth |
| High P/E (20+) | Strong growth expectations | Growth premium or possible overstatement |
A high p/e may indicate exceptional growth prospects or a speculative bubble, while a low ratio may indicate a buying opportunity or structural difficulties.
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Comparison of labour force by sector of activity
P/E ratios vary considerably by sector of activity due to their specific economic characteristics:
- Technology : P/E often high (25-40) due to growth potential
- Public services : Moderate P/E (12-18) reflecting income stability
- Banques : P/E generally lower (8-15) due to sector cycling
- Industry : P/E variables according to economic cycles
Limits and precautions for the use of PER
The p/e ratio has several important limitations to consider. Accounting profits can be manipulated by aggressive accounting techniques, thus distorting the calculation. Companies in loss do not have a computable P/E, making the analysis impossible for companies in restructuring.
In addition, the P/E does not take into account debt, future growth or the quality of profits, requiring further analysis with other financial indicators.
Use of p/e in investment strategy
Selection of actions with ratio p/e
Investors use the p/e ratio using different strategic approaches. Investment value favours low-P/E shares, seeking market undervalued opportunities. This strategy requires an in-depth analysis to distinguish between real opportunities and « value traps ».
On the contrary, the momentum approach can target high P/Es, betting on the continuation of growth and expansion of multiple valuations. This strategy works particularly well in bullish markets.
Combination with other financial indicators
The efficiency of the p/e ratio increases when combined with other financial metrics:
- Price/Book ratio (P/B) : complete valuation analysis
- Return on Equity (ROE) : evaluates the profitability of equity
- Profit growth rate : justifies high P/E
- Debt ratio : reveals financial risks
This multifactorial approach allows for a more balanced assessment and reduces the risk of investment error based on a single indicator.
Summary for an informed investment
The p/e ratio remains a fundamental tool for financial analysis, providing a first quick approach to the valuation of a business. Its simplicity of calculation and interpretation makes it an indicator accessible to all investors, from beginners to professionals. However, its optimal use requires an understanding of its limitations and integration into a broader financial analysis, combining several ratios and a qualitative assessment of the company and its sector of activity.