P/E Ratio Calculator

What the number represents

Share price divided by earnings per share. A P/E of 20 means paying 20 for each 1 of annual earnings, or equivalently that the company would take 20 years to earn back its price at current profitability. Inverting it gives the earnings yield — a P/E of 20 is a 5 percent earnings yield, which is the form that compares directly against bond yields.

A low P/E is usually a warning, not a bargain

Markets price in expectations. A company trading at 6 when its sector trades at 18 is generally not overlooked; the market expects earnings to fall, so the ratio is low because the denominator is about to shrink. This is the value trap, and screening for low P/E without asking why selects for declining businesses. The genuine bargains are the cases where the market is wrong, and they are rare by construction.

Trailing and forward answer different questions

Trailing P/E uses the last twelve months of reported earnings — factual but backward-looking. Forward P/E uses analyst estimates, which are forward-looking but frequently optimistic. A cyclical company at the peak of its cycle shows a flatteringly low trailing P/E precisely when it is most expensive, which is the opposite of what the number appears to say.

Comparison only works within a sector

Software companies routinely trade at 30 to 50 because earnings are expected to grow fast; utilities trade at 12 to 18 because they will not. Comparing across sectors measures growth expectations rather than relative value. Comparing a company against its own history and its direct peers is where the ratio earns its keep.

Negative and missing earnings break it entirely

A loss-making company has no meaningful P/E, and tools display it as negative or blank. Early-stage and heavily reinvesting businesses fall into this category permanently, which is why price-to-sales or EV/EBITDA are used instead. A P/E of 400 usually signals earnings near zero rather than extreme overvaluation.

Earnings are an accounting figure

One-off charges, asset sales, tax settlements and write-downs all move reported earnings without changing the underlying business. A P/E computed on a quarter containing a large one-off is not comparable to the previous one. Checking whether earnings were unusual is worth more than three decimal places of precision on the ratio.