The price-to-earnings ratio formula
The price-to-earnings ratio is share price divided by earnings per share: price-to-earnings ratio = share price ÷ earnings per share. The share price is what one share costs on the market today. Earnings per share is the company’s profit for the year, divided by the number of shares. The answer is a multiple, not a dollar amount: 25.00 means twenty-five dollars of price for each dollar of annual earnings. Try the numbers on the price-to-earnings ratio calculator and it does the division for you.
Step 1: find the share price
Start with the market. The share price is the price one share trades at today — the number on the quote page, the brokerage app, the market data site. Here is the worked example: a share price of $150.00. Use the price on the day you are judging the stock.
Step 2: find the earnings per share
Start with the company’s accounts. Earnings per share is the company’s profit for the year, divided by the number of shares in issue — the figure on the income statement, per share. Here is the worked example: earnings per share of $6.00. Use the same year for both numbers, and use trailing-twelve-month earnings when you compare across years, because one quarter alone can mislead for seasonal businesses.
Step 3: divide and read the answer
Divide the share price by the earnings per share. Here is the worked example: $150.00 ÷ $6.00 = 25.00. The arithmetic is $150.00 ÷ $6.00 = 25.00, so each $1 of annual earnings costs $25.00 of price. The answer is a multiple, not a dollar amount — write it as 25.00, not $25.00. Roughly, it is twenty-five years of current earnings to pay back the price, if earnings never grew.
Three worked examples
Example one — the headline numbers. A stock costs $150.00 a share and earns $6.00 a share. The price-to-earnings ratio is $150.00 ÷ $6.00 = 25.00. Each $1 of annual earnings costs $25.00 of price.
Example two — trailing twelve months. A seasonal business earns $1.50 a share in the first quarter, $1.60 in the second, $1.40 in the third and $1.50 in the fourth — $6.00 for the year. Its share price is $150.00. The ratio is $150.00 ÷ $6.00 = 25.00. One quarter alone would have misled you.
Example three — how much must it earn? A stock costs $150.00 a share and you want a 20.00 P/E. The earnings per share needed is $150.00 ÷ 20.00 = $7.50 — the earnings the company must reach for the multiple to fall to the target on the price it already has.
One reverse to check your answer
Work the numbers backwards to check them. A stock earns $6.00 a share and you want its P/E to reach 20.00. The smallest whole-cent share price for the P/E to reach the target is $120.00 — $120.00 ÷ $6.00 is exactly the target. A cent less, and the price is $0.01 short of the $120.00 needed. The price-to-earnings ratio calculator runs the reverses for you.
Share price vs earnings per share
The share price is what the market charges today — it moves every second the market is open, and it is the same for every buyer. Earnings per share is what the company earned — it moves four times a year, when the accounts come out, and it is the same for every share. The ratio joins them: the price the market charges against the profit the company made. When the price rises and earnings stay put, the ratio rises; when earnings rise and the price stays put, it falls.
What a high P/E means
A high P/E means the market pays a lot for each dollar of earnings — it expects the earnings to grow. Above 25 is expensive by the rough yardstick — but the bar moves by sector: fast-growing technology stocks often run above 30 because investors pay for future earnings, while banks and utilities often run below 15 because their earnings grow slowly, so compare within one industry, not across them.
What a low P/E means
A low P/E means the market pays little for each dollar of earnings — it expects the earnings to stay flat, or it doubts them. Below 15 is cheap by the rough yardstick — but a cheap multiple can mean a bargain, or a business in trouble. The S&P 500’s long-run average P/E is roughly 16, so a P/E near 16 is the middle of the market.
Trailing vs forward P/E
The trailing P/E uses the last twelve months of earnings — what the company actually earned. The forward P/E uses forecast earnings — what analysts expect it to earn — and it is usually lower, because earnings are expected to grow. Use the trailing P/E when you want facts, and the forward P/E when you want the market’s guess. Never mix them: a trailing 25.00 against a forward 20.00 is two different measures.
The P/E vs the dividend yield
The dividend yield is the dividend per share divided by the share price — income per dollar of price — while the P/E is the share price divided by earnings per share — price per dollar of earnings. They are two sides of the same coin: check both before you judge. Read the guide to the dividend yield and try the dividend yield calculator and the gross profit margin calculator for the profit side.
What to do when the P/E is high
Two levers bring the multiple down. More earnings: the company grows its profit, and the same price buys a lower multiple. A lower price: the market falls, and the same earnings cost less. The P/E does not account for growth, debt, or cash — a company can look cheap on P/E while carrying heavy debt, so cross-check with the cash flow margin and the operating cash flow ratio before you buy.
Why compare within one industry
The bar moves by sector. Fast-growing technology stocks often run above 30 because investors pay for future earnings, while banks and utilities often run below 15 because their earnings grow slowly. Compare a stock with its own sector, its own history, and the market average — roughly 16 for the S&P 500 — and judge the growth, not the multiple alone.