When a Margin-of-Safety Number Stops Meaning What You Think It Means

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A margin of safety is arithmetic on two inputs, earnings and book value, and it is exactly as trustworthy as those two inputs. In our September 27 screen, 33 stocks cleared the quantitative filters. Reading through the report, I found one name where the earnings input is distorted, one where the book value input was a year out of date, and one where both inputs are accurate and the number still protects nothing. The single stock that earned a PASS trades above its Graham Number altogether.

None of that makes the margin of safety a bad tool. It makes it a calculation, and a calculation deserves the same scrutiny as the figures fed into it.

The Graham Number is a rule solved for price

Benjamin Graham told defensive investors to pay no more than 15 times earnings and no more than 1.5 times book value, and he allowed the two to trade off as long as their product stayed under 22.5. Solve that rule for price and you get the Graham Number: the square root of 22.5 × earnings per share × book value per share. The margin of safety is the gap between that figure and the market price.

So there are only three places the number can fail. The E can be wrong. The B can be wrong. Or both can be right and the claim they describe can be one you cannot enforce.

Kennametal: earnings the cash flow statement does not support

Kennametal (NYSE: KMT) cleared our quantitative screen with a trailing P/E of 7.0, a current ratio of 2.62 and a 40-year dividend record. We rated it WATCH.

The reason is in the fiscal 2026 results. Net income was $342.4 million, up from $93.1 million a year earlier, and diluted EPS went from $1.20 to $4.42. Over the same twelve months, cash from operating activities was negative $4.0 million, against positive $208.3 million the year before (fiscal 2026 results). The company's own release puts the benefit from "favorable timing of raw material-related pricing compared to raw material costs" at approximately $316 million for the year, $252 million of it in the fourth quarter alone. Selling prices rose with tungsten faster than the higher-cost material moved through cost of goods sold. Inventory, meanwhile, roughly doubled, from $538.2 million to $1,108.5 million. That is where the cash went.

Now run the margin of safety three ways, holding book value at $20.60 per share and the price at $31.03:

Same company, same day, and the answer swings from a comfortable discount to a steep premium depending on which year you believe. Our report uses the three-year average, which is why it shows 6%. On fiscal 2025 earnings alone, the P/E is about 26, more than double our ceiling of 12.

This is the same shape as the bird-flu year at Cal-Maine, which I wrote about in When One Great Year Makes a Stock Look Cheap. The business is sound. The earnings figure is not yet a reliable anchor.

Teekay Tankers: a book value that was a year old

The second input fails more quietly. Our September 27 report showed Teekay Tankers (NYSE: TNK) with a Graham Number of $127.74 and a 26% margin of safety at a $94.07 share price. That Graham Number was built on the $59.15 book value per share in the 2025 annual report.

By then the company had reported a record second quarter, and book value per share stood at $68.51. Put that figure into the same formula and the Graham Number rises to $137.47. The margin of safety at the same price becomes about 32%. I walked through the full recalculation in the Teekay Tankers check-in.

Here the stale input understated the cushion. It can just as easily run the other way: a company that has taken write-downs or paid out large special dividends since its last annual report will show a book value, and a margin of safety, that no longer exists. A book value is a dated figure, and the date belongs next to it.

FinVolution: accurate inputs, and a number that still protects nothing

FinVolution (NYSE: FINV) trades at 3.5 times earnings and 0.43 times book value. Nothing about those inputs is distorted or stale. It received an automatic FAIL.

FinVolution's ADS holders own shares in an offshore holding company whose access to the operating business in China runs through contracts with a variable interest entity, not through equity ownership. A margin of safety rests on an assumption so basic it usually goes unstated: if things go badly, the assets and earnings in the calculation belong to you. With a VIE, what belongs to you is a contract. I covered the record of how those contracts have held up in Why We Automatically Fail Every Chinese VIE.

A stock at less than half of book looks like the widest cushion in the report. It is a cushion made of assets the shareholder cannot reach.

The one stock that passed trades above its Graham Number

The reverse case is the most instructive. Exactly one stock in the September 27 report earned a PASS, and its price is roughly 12% above its Graham Number. On that measure it has no margin of safety at all.

It qualifies because the gate was never the Graham Number. Our screen applies Graham's combined test with stricter limits: a stock whose price-to-book is above 1.5 can still qualify if P/E times P/B stays under 18. This one comes in near 12. The difference between the two views is, once again, the earnings input. The combined test runs on trailing earnings, which for this company are more than double the three-year average that feeds its Graham Number.

Which figure deserves more weight is a judgment about the business, and it is the judgment the filing review exists to make. In this case the review found the recent earnings backed by cash. For Kennametal it found the opposite. The arithmetic was the same both times.

Five checks before you trust the number

1. Does operating cash flow roughly track net income? A large gap in one year is the first sign that the E is borrowed from the future.
2. What date is the book value from? Check it against the most recent quarterly filing, not the last annual report.
3. Is tangible book value close to stated book value? If most of the B is goodwill, the cushion depends on what someone once paid for an acquisition.
4. Do you own equity or a contract? For foreign issuers, read the corporate structure section of the 20-F before anything else.
5. Are the price and the per-share figures in the same currency and the same share unit? An ADS can represent several ordinary shares, and the financial statements are often in a currency other than the dollar. Mix them and the result is meaningless.

Where these checks can mislead you

Normalizing earnings is a judgment call. Kennametal's management is guiding to adjusted EPS of $4.15 to $5.15 for fiscal 2027, so the company does not expect earnings to fall back toward $1.20. If tungsten prices hold, WATCH will prove too cautious. The same guidance puts free operating cash flow at about 20% of adjusted net income, which is why I am not ready to take the earnings at face value either.

Stale inputs cut both ways. Refreshing Teekay's book value made the stock look cheaper, not more expensive. Skepticism about an input is a reason to check it, not a reason to assume the error runs against the stock.

A hard gate excludes good businesses. The VIE rule is about the claim, not the company. Some of those businesses will do well, and holders of the ADSs may do well with them.

None of this predicts price. These are tests of whether a number means what it says. A stock can fail every one and rise for years.

The number is where the work starts

The margin of safety is still the most useful single figure in value investing. Its limit is that it reports the output of a formula with the confidence of a fact. In one report, three stocks showed three different ways the output can drift from reality, and the one clean PASS did not depend on it at all.

That is why every figure in our report sits next to a reading of the filing it came from. The next screen runs October 11. I will be watching whether Kennametal's first-quarter cash flow starts converting that inventory, and what Teekay's third-quarter results do to its book value.