Yes, a stock can have a negative pricetoearnings ratio (P/E), but it is very unlikely that you will ever see it reported. Although negative P/E ratios are mathematically possible, they generally aren't accepted in the financial community and are considered to be invalid or just not applicable. We'll explain why this is.
The priceearnings ratio is arguably the most popular fundamental factor used by investors who try to determine the attractiveness of an asset's current value and, more importantly, whether the current price level makes for a good buying opportunity. The ratio is calculated by dividing a financial asset's current share price by its pershare earnings. Generally speaking, a low P/E value suggests that an investor needs to pay a low amount for each dollar of earnings made by the company. This could be used by investors as a sign that the given asset is undervalued and a potentially good investment at current levels. Conversely, a relatively high P/E value is used to suggest that investors will need to pay a high amount for the company's earnings, which can then be used to suggest that the asset is relatively expensive and that it may be a good idea to wait for a better entry.
Mathematically, there are only two ways for a ratio of this form to have a negative value:
 The numerator falls below zero
 The denominator falls below zero.
In the case of the P/E ratio, it is impossible for the numerator to fall below zero because this represents the price of the asset. However, the denominator, which is equal to the earnings of the company, can become negative. EPS values below zero mean that the company is losing money and is the reason why it is possible to have a negative P/E ratio.
Negative EPS numbers are usually reported as "not applicable" for quarters in which a company reported a loss. Investors buying a company with a negative P/E should be aware that they are buying a share of a company that has been losing money per share of its stock.
For further reading, see our tutorials on Understanding the P/E Ratio and Ratio Analysis.

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