CAPE Ratio (Shiller P/E)

The CAPE ratio, or Shiller P/E, divides price by the average of ten years of inflation-adjusted earnings. Smoothing a full decade of profits strips the business cycle out of the denominator, so the multiple reflects what buyers pay for sustainable earning power rather than for one unusually good or bad year.

The math

Suppose an index trades at 4,800 while its ten-year average of real earnings sits at $150 per unit: a CAPE of 32. At a multiple of 20 on the same earnings, the index would sit at 3,000.

	At CAPE 32	At CAPE 20
Ten-year avg real earnings	$150	$150
Index level	4,800	3,000
$100,000 position	$100,000	$62,500

If valuation drifts back toward that level over a decade, a $100,000 position must absorb a $37,500 headwind from the multiple alone, and earnings growth has to replace every dollar of it before producing any actual return. The drag arrives silently, costing a point or two of performance per year.

The trap

Using CAPE as a timing signal. Expensive markets can get more expensive for years, and an investor who moved to cash at a CAPE of 25 to wait for reversion may watch it climb past 30 while compounding continues without him.

CAPE describes the odds and the size of the eventual prize; it says nothing about the date.

The move

Let CAPE set expectations, not positions. When the broad market’s CAPE is stretched, the index itself becomes the overpriced asset, and that is precisely when selection earns its keep: individual businesses still trade at ordinary multiples inside an expensive average.

Apply the same logic to single stocks through normalized earnings, and demand a wider margin of safety whenever the whole market is priced for perfection.