The Treasury Stock Method for Diluted Shares

Six million options, and the diluted share count goes up by 3,600,000. Where did the other 2,400,000 go? You see this gap whenever you set the stock compensation note of a 10-K beside the diluted share line on the income statement, and it is the treasury stock method at work.

The method treats an option exercise as two transactions stacked together. The holder pays the strike price and receives new shares. Then the company, in theory, takes the cash to the market. It buys its own stock back at the going price. Only what is left over after the buyback counts as dilution.

The sum

A hypothetical company has 6,000,000 options outstanding with a $20 strike. The stock trades at $50.

The formula is the short version of the same story. Strike divided by share price is the fraction of the new shares the cash can buy back. Subtract it from one. What remains stays in the count.

Push the share price higher and the net number grows. At $100, the same grant adds 4,800,000 shares. The same $120,000,000 now retires only 1,200,000. That link between the stock price and the diluted count is easy to miss: a rally can raise the share count used for EPS even in a quarter when the company granted nothing new.

Options priced above the market

Now suppose the strike is $60 and the stock is at $50. The formula turns negative. The buyback would retire more shares than the exercise creates. Counting that would shrink the diluted base and flatter EPS. Accounting rules call such instruments anti-dilutive and leave them out entirely.

You can usually find the excluded amount in the EPS footnote, stated as a number of options or warrants not included because their effect was anti-dilutive. Read it anyway, because those instruments come back into the count the moment the share price climbs past their strike, and a company with a thick layer of options just above the market can see its diluted base step up sharply in a single strong quarter.

How it shows up in a filing

Filings do not usually print the calculation. What you get is a reconciliation in the EPS note: basic weighted average shares, then a line for the dilutive effect of options and restricted stock units, sometimes one for warrants, then the diluted total. That options line is this method’s output. Restricted stock units have no strike. The method still covers them, with the compensation cost the company has yet to recognize standing in for exercise cash, so most of each unit ends up in the count.

Two inputs sit elsewhere. The option count and weighted average exercise price are in the stock compensation note. Warrants and their exercise prices are usually in the equity footnote. The company uses the average share price for the period, which is why your back-of-envelope figure using today’s quote rarely matches the reported line exactly.

What people get wrong

The commonest error is adding every option and warrant in full. That is the fully diluted share count, a larger and more conservative number. The treasury stock method gives fewer shares for in-the-money instruments and none for out-of-the-money ones.

Another is forgetting that the method runs on warrants too. A company carrying a large block of warrants from a past financing can see its diluted count jump as the stock rises through their exercise price, which is the case made in stock warrants are dilution on a delay.

Convertible debt has its own rule. The if-converted method assumes the notes become shares and adds the after-tax interest back to earnings, so keep the notes out of this formula.

Test other strikes and prices in the share dilution calculator. The wider set of valuation topics is under investing.