How earnings per share works

Earnings per share is one division:

$$\text{EPS} = \frac{\text{Earnings}}{\text{Shares outstanding}}$$

On $250,000,000 of earnings and 100,000,000 shares, EPS is $2.50. Price over that EPS is the price to earnings ratio. A $50 share on $2.50 is 20 times. Market capitalisation over total earnings is the same 20: $5,000,000,000 / $250,000,000.

The two routes are the same identity. Multiplying price and EPS by the share count cancels, so market cap over total earnings cannot disagree with price over EPS unless one of the three inputs is from a different date than the others.

The price to earnings calculator on this page works both routes from one set of figures. How the P/E ratio works is the multiple. This page is the denominator.

Keep the $50 price and 100,000,000 shares. Raise EPS to $5.00. P/E falls to 10. Market cap is still $5,000,000,000. Total earnings are now $500,000,000.

The price did not move. The denominator did. A lower P/E here is a more profitable year, not a cheaper share. That is why a low P/E at the top of a cycle, when earnings are at a peak that will not repeat, can be the expensive reading: the market is already looking through the peak, and the ratio is being divided by a number that is about to shrink.

Type the EPS your sheet is using. Trailing EPS uses the last twelve months of reported earnings. Forward EPS uses estimates for the year ahead. They are not interchangeable. Trailing against forward P/E is that split on the multiple. The split starts in this denominator.

Price is now $80, EPS still $2.50, shares 50,000,000. P/E is 32. Market cap is $4,000,000,000. Total earnings are $125,000,000.

The same $2.50 of EPS on half the shares and a higher price is a smaller firm with a higher multiple. EPS hides scale. So does P/E. Neither one tells you whether you are looking at a $5,000,000,000 firm or a $4,000,000,000 firm until you put the share count back in.

Buybacks cut the share count and raise EPS even when total earnings do not move. Issuing shares does the opposite. A rise in EPS that came from a smaller count is a different claim from a rise that came from a larger profit.

When earnings are zero or negative the P/E ratio stops working. Dividing a price by a loss does not produce a useful multiple. This calculator prints no P/E in that case rather than a nonsense figure. EPS itself can still be written as a negative: a loss of $250,000,000 on 100,000,000 shares is a loss of $2.50 a share. That is a description of the year. It is not a multiple.

Loss-making firms get compared on revenue, or on a different multiple, not on P/E. How enterprise value works is the operations-side cousin that can still be formed when equity earnings are negative, because the denominator there is a flow such as EBITDA rather than residual profit.

Basic EPS uses shares actually outstanding. Diluted EPS adds in options, convertibles and the rest of the potential count. A firm with a large option overhang can print a comfortable basic EPS and a much thinner diluted one. The P/E on this page takes the EPS you type, so the choice of basic or diluted is yours and has to match the price's date.

Earnings themselves can be reported, adjusted, or estimated. Mixing a trailing reported EPS with a forward price, or an adjusted EPS with a reported peer, is how a cheap-looking name appears next to an expensive-looking one that is actually the same firm on two different denominators.

It is not a trailing-against-forward switch, not a dilution engine, and not a buy or sell. The three sheets are a $50 share on $2.50 of EPS (P/E 20, earnings $250,000,000), the same price on $5.00 of EPS (P/E 10, earnings $500,000,000), and an $80 share on 50,000,000 shares (P/E 32, earnings $125,000,000). This is educational material, not financial advice.