What is Shiller PE Ratio?
The Shiller PE, or “CAPE Ratio” is a variation of the price to earnings ratio adjusted to remove the effects of cyclicality, i.e. the fluctuations in the earnings of companies over different business cycles.
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How to Calculate Shiller PE (CAPE Ratio)
The Shiller PE, or CAPE ratio, refers to the “Cyclically Adjusted Price to Earnings Ratio”, and the rise in its usage is attributed to Robert Shiller, a Nobel Prize-winning economist and renowned professor at Yale University.
Unlike the traditional price to earnings ratio (P/E), the CAPE ratio attempts to eliminate fluctuations that can skew corporate earnings, i.e. “smoothen” the reported earnings of companies.
In practice, the use-case of the CAPE ratio is to track broad market indices, namely the S&P 500 index.
- Traditional P/E Ratio → The traditional P/E ratio uses the reported earnings per share (EPS) from the trailing twelve months as the denominator.
- CAPE Ratio (Shiller PE 10) → Conversely, the CAPE ratio is unique in that the average annual earnings per share (EPS) over the trailing ten years is used, instead.
However, taking the average of a company’s reported EPS figures in the past ten years neglects a critical factor that affects the financial performance of all corporations, which is inflation.
In economics, the term “inflation” is a measure of the rate of change in the pricing of goods and services within a country across a specified time frame.
While there is significant criticism (and controversy) surrounding the methodology by which inflation is measured, the Consumer Price Index (CPI) remains the most common measure of inflation in the U.S.
The process of calculating the Shiller PE ratio can be broken into a four-step process:
- Step 1 → Gather the Annual Earnings of the S&P Companies in the Trailing 10 Years
- Step 2 → Adjust Each of the Historical Earnings by Inflation (i.e. CPI)
- Step 3 → Calculate the Average Annual Earnings for the 10-Year Time Horizon
- Step 4 → Divide the 10-Year Average Earnings by the Current Price of the S&P Index
Shiller PE Formula (CAPE Ratio)
The formula to calculate the Shiller PE (CAPE Ratio) divides the current share price of a company by its inflation-adjusted earnings, expressed on a 10-year average basis.
The CAPE ratio most often serves as a market indicator, so the share price refers to the market price of a stock market index.