Diluted shares and the treasury stock method
5 min read · updated July 8, 2026
Ask how many shares a company has and you will get two different answers, both correct. There is the number of shares that exist today, and there is the larger number that would exist if everyone holding a claim on new shares cashed it in. Valuation, earnings per share, and every accretion/dilution question turn on the second one, so you have to know how to get from the first to the second.
Basic versus diluted shares
Basic shares outstanding is the straightforward count: the shares that exist and trade right now. Diluted shares outstanding adds the shares that would be created if every in-the-money option, warrant, and similar claim were exercised. Diluted is always greater than or equal to basic, never less.
The reason the gap exists is that companies hand out claims on future shares. When those claims convert, the share count grows and each existing owner holds a slightly smaller slice of the same company. That shrinking of ownership is what "dilution" means.
Where the extra shares come from
Most dilution traces back to a few sources, and you should be able to name them:
| Source | What it is |
|---|---|
| Employee stock options | The right to buy a share at a fixed strike price, usually granted as pay |
| Restricted stock units (RSUs) | Promised shares that vest over time |
| Warrants | Like options, but usually issued to investors rather than employees |
| Convertible debt or preferred | Bonds or preferred stock that can convert into common shares |
Options and warrants are handled with the treasury stock method below. Convertibles use a related idea called the if-converted method, but options are what interviewers test, so master these first.
The treasury stock method
Here is the trap. It is tempting to say that a company with 1,000,000 options outstanding simply adds 1,000,000 shares when they are exercised. That overstates the dilution, because exercising an option is not free. The holder has to pay the strike price to the company, and that cash does not vanish.
The treasury stock method captures this. It assumes the company takes the cash it receives from option holders exercising and immediately uses it to buy back its own shares at the current market price. Only the leftover, unbought shares actually dilute.
Three inputs drive it. is the number of options. is the strike price, the fixed price the holder pays per share. is the current market price of the stock. The net new shares created are:
Walk through it with numbers. A company has 10,000,000 basic shares. It has granted 1,000,000 options with a strike price of $10, and the stock trades at $25.
- Exercising all options sends the company 1,000,000 × $10 = $10,000,000 in strike proceeds.
- The method assumes the company spends that $10,000,000 buying back stock at $25 per share: $10,000,000 / $25 = 400,000 shares repurchased.
- Net new shares are the 1,000,000 issued minus the 400,000 bought back, which is 600,000.
So the diluted share count is 10,000,000 + 600,000 = 10,600,000, not 11,000,000. The shortcut formula gets there in one step: 1,000,000 × (25 - 10) / 25 = 1,000,000 × 0.6 = 600,000.
Only the "in-the-money" spread dilutes. Because the company recovers the strike price and reinvests it in a buyback, the net dilution reflects only the gain portion, the gap between market price and strike. The bigger that gap, the more each option dilutes. This is why a rising stock price actually increases a company's diluted share count.
Out-of-the-money options do not count
An option is in the money only when the market price is above the strike, so exercising it is profitable. If the strike is $30 and the stock trades at $25, no rational holder exercises, because they would be paying $30 for something worth $25. Those options are out of the money and are excluded from the diluted count entirely.
Adding every option to the share count, or including out-of-the-money options. Both overstate dilution. You add only in-the-money options, and only their net effect after the assumed buyback. When the stock is below the strike, those options contribute zero dilution until the price recovers.
Why this is the number that matters
Diluted shares, not basic, is what you use almost everywhere that counts.
Equity value is share price times fully diluted shares outstanding, because a buyer of the whole company inherits those option claims and has to account for them. Use basic shares and you understate what the equity is really worth. Diluted earnings per share divides net income by the diluted count, which is always less than or equal to basic EPS because the denominator is larger. And accretion/dilution analysis in a merger runs entirely on pro forma diluted EPS, so getting the share count right is the whole game.
If asked to compute equity value or diluted EPS, say "fully diluted" out loud and reach for the treasury stock method without being prompted. A common curveball is to give you options and ask for the diluted count. Do the two steps in your head: proceeds divided by price gives the buyback, issued minus buyback gives the net new shares. Then add them to basic. Naming that the strike proceeds fund a buyback is what signals you actually understand the mechanic rather than memorizing a formula.
Glossary
New to the lingo? Every term used above, in plain English.
- Dilutive security
- Any claim that can turn into new common shares and shrink existing owners’ slice of the company, such as employee stock options, restricted stock units, warrants, or convertible debt.
- Treasury stock method
- The standard way to count how many net new shares options and warrants create. It assumes the company takes the cash it receives when holders pay the strike price and immediately buys back shares at the market price, so only the leftover shares dilute.
- In the money
- An option is in the money when the current stock price is above its strike price, so exercising it is profitable. Only in-the-money options count toward diluted shares; out-of-the-money ones (strike above the price) are ignored.
- EPS (Earnings Per Share)
- A company’s profit divided by its number of shares. It is the per-share slice of earnings that each shareholder owns.
- Equity Value
- The slice of a company that belongs to its shareholders. For a public company this is the market capitalization (share price times shares outstanding).
Make it stick
Drill what you just learned