It's easy enough to calculate, since you take the stock's price and divide it by the company's earnings per share. For example, if Plain Bagel Co. had 1 million shares outstanding, each of which were trading at a price of $30, and last year their net income was $2 million, the stock's P-E ratio would be 15 times. This P-E ratio is known as a trailing P-E, because we're calculating it using historical information, and it's one of the easiest multiples to understand. It basically represents how much an investor is willing to pay per dollar of a company's profits. So for Plain Bagel Co., we are paying a price equal to 15 times our share of the company's profit. So the trailing P-E helps conceptualize how much we're paying for a stock, but it does have its shortcomings. The biggest one being that it is backwards-looking, whereas many believe that markets are forward-looking. If a company is expected to release a new product, enter a new market, or improve its operations in the future, then a stock will likely trade higher, something that the trailing P-E wouldn't take into account using past earnings to explain the stock's current price. Because of this, many investors prefer instead to use what's known as a forward multiple, in this case the forward P-E, which divides a stock's price by how much the company is expected to make next year.
株価を一株当たり利益で割るのだから、計算するのは簡単だ。例えば、プレーン・ベーグル社の発行済み株式数が100万株で、その1株あたりの株価が30ドル、昨年の純利益が200万ドルであったとすると、株価のP-Eレシオは15倍となります。このP-Eレシオは、過去の情報を使って計算するため、トレーリングP-Eとして知られており、最も理解しやすい倍率の一つである。基本的には、投資家が企業の利益1ドルあたりいくらなら支払ってもいいと考えているかを表しています。つまり、プレーン・ベーグル社の場合、私たちは会社の利益の15