Earnings yield is the inverse of the price-to-earnings multiple. A stock with a 10 multiple has a 10 percent earnings yield; a stock with a 20 multiple has a 5 percent earnings yield. Earnings yield is directly comparable to a bond yield — both express what the security currently earns expressed as a percentage of its current price.
Quantitative Margin of Safety (percentage points) = Earnings Yield − AAA Corporate Bond Yield
| AAA bond yield environment | Graham defensive threshold (earnings yield) | Implied maximum price-to-earnings multiple |
|---|---|---|
| 3 percent (low-rate regime) | About 6 percent earnings yield (two times AAA) | Roughly 16 to 17 times earnings |
| 5 percent (medium-rate regime) | About 10 percent earnings yield | Roughly 10 times earnings |
| 7 percent (high-rate regime) | About 14 percent earnings yield | Roughly 7 times earnings |
The rate-regime adjustment is the load-bearing part of the test. Applying a fixed multiple cutoff from a low-rate decade to a high-rate decade — or vice versa — silently changes the margin in dangerous ways. The honest application is always to compare the current earnings yield to the current AAA bond yield, not to a fixed numerical threshold lifted from a different era.
What the test does not do. The quantitative margin test cannot tell you whether the earnings number you fed it is real, sustainable, or growing. A cyclical business at the peak of its cycle can show a deeply attractive earnings yield right before the trough collapses the number. An asset-light business with declining returns on capital can show an attractive yield even as its long-run economic value erodes. The yardstick screens for price-to-current-earnings cheapness; it does not screen for business quality, durability, or the honesty of the accounting. Graham himself paired the quantitative test with separate filters for earnings stability over a multi-year window, an unbroken dividend record, and a strong balance sheet.
Sit with the ideas.
Whitcombe Industrial trades at $48 per share, earns $4.80 per share in normalized operating earnings, and operates in an environment where AAA corporate bonds yield about 5.5 percent. Apply Graham's quantitative margin-of-safety test in its rate-adjusted form — how attractive is the stock by the test, and what does the result actually tell you?