The treasury stock method (TSM) is one of the most frequently tested technical concepts in investment banking interviews. It is the standard way to calculate the dilutive impact of stock options and warrants on a company’s share count. If you cannot walk through the treasury stock method clearly and confidently, you are not ready for your interview.
In this guide, we will explain the logic behind the treasury stock method, walk through the calculation step by step with a detailed numerical example, and cover the edge cases and follow-up questions you might encounter.
What Is the Treasury Stock Method?
The treasury stock method is an accounting approach used to calculate the net increase in shares outstanding that would result from the exercise of in-the-money stock options and warrants. The key insight is that when option holders exercise their options, the company receives cash (the exercise price times the number of options). The TSM assumes the company uses that cash to buy back shares in the open market at the current price, partially offsetting the dilution.
The result is a “net” dilution figure that is always less than the gross number of options outstanding because the buyback offsets some of the new shares created.
Why the Treasury Stock Method Matters
The TSM matters because it directly impacts two of the most important numbers in valuation:
- Diluted shares outstanding: You need diluted shares to calculate equity value (share price x diluted shares), which is the starting point for the equity value bridge to enterprise value.
- Diluted EPS: Companies report diluted earnings per share, which uses the diluted share count from the TSM in the denominator.
- Implied share price in a DCF: At the end of a DCF analysis, you divide implied equity value by diluted shares to get the implied price per share. If you get diluted shares wrong, your implied price will be wrong.
The Logic Behind the TSM
Let us think about what happens when an employee exercises stock options:
Step 1: The employee pays the exercise price to the company and receives new shares. This increases the total shares outstanding.
Step 2: The company now has cash from the exercise proceeds. The TSM assumes the company uses this cash to repurchase shares on the open market at the current market price.
Step 3: The net increase in shares is the difference between the shares issued (Step 1) and the shares repurchased (Step 2).
This is a simplifying assumption: in reality, companies do not automatically buy back shares when options are exercised. But it is the standard convention used by accountants (under GAAP and IFRS) and by investment bankers for calculating diluted shares.
Step-by-Step Calculation
Here is the treasury stock method calculation broken down into clear steps:
Given Information
- Basic shares outstanding: 200 million
- Stock options outstanding: 20 million
- Weighted average exercise price: $25
- Current share price: $50
Step 1: Check if Options Are In the Money
Compare the exercise price ($25) to the current share price ($50). Since $25 < $50, these options are in the money and should be included in the diluted share count. If the exercise price were above $50, you would exclude these options entirely: they are antidilutive because no rational holder would exercise them.
Step 2: Calculate Shares Created from Exercise
If all 20 million options are exercised, 20 million new shares are created.
Shares created = 20 million
Step 3: Calculate Exercise Proceeds
The company receives the exercise price for each option exercised:
Proceeds = 20 million options x $25 exercise price = $500 million
Step 4: Calculate Shares Repurchased
The company uses the $500 million in proceeds to buy back shares at the current market price:
Shares repurchased = $500 million / $50 per share = 10 million shares
Step 5: Calculate Net New Shares
Net new shares = Shares created − Shares repurchased = 20 million − 10 million = 10 million
Step 6: Calculate Diluted Shares Outstanding
Diluted shares = Basic shares + Net new shares = 200 million + 10 million = 210 million
So the diluted share count is 210 million, an increase of 5% over the basic count. This is the number you would use to calculate equity value, diluted EPS, or the implied share price from a DCF.
The Shortcut Formula
For interviews, you can use this condensed formula to calculate net new shares quickly:
Net New Shares = Options x (Share Price − Exercise Price) / Share Price
Using our example: 20 million x ($50 − $25) / $50 = 20 million x 0.5 = 10 million. Same answer, one step.
This formula works because it algebraically simplifies the full calculation. The term (Share Price − Exercise Price) / Share Price represents the portion of each option that creates real dilution after accounting for the buyback.
Handling Multiple Tranches of Options
In practice, companies have options at many different exercise prices. The company’s 10-K footnotes (usually in the stock-based compensation section) will show a table breaking down options by exercise price range. Here is how to handle it:
- Apply the TSM separately to each tranche of options at a given exercise price.
- Only include tranches where the exercise price is below the current share price (in the money).
- Sum the net new shares from all in-the-money tranches.
- Add the total net new shares to basic shares outstanding.
For example, suppose a company trading at $50 has three tranches:
- 5 million options at $20 strike: in the money, net dilution = 5M x ($50 − $20)/$50 = 3 million
- 8 million options at $35 strike: in the money, net dilution = 8M x ($50 − $35)/$50 = 2.4 million
- 4 million options at $55 strike: out of the money, excluded
Total net new shares = 3 million + 2.4 million = 5.4 million.
RSUs and the Treasury Stock Method
Restricted stock units (RSUs) do not have an exercise price: they are granted to employees for free. Because there are no exercise proceeds, there is no buyback to offset the dilution. RSUs that are expected to vest are simply added to the diluted share count at their full amount.
However, there is a nuance: unvested RSUs may or may not be included depending on whether you are using the GAAP diluted share count or a market convention. For financial reporting, GAAP uses a “contingently issuable shares” approach that may include only a portion of unvested RSUs. For investment banking purposes, many bankers include all outstanding RSUs (vested and unvested) to be conservative.
Convertible Securities: The If-Converted Method
The treasury stock method applies to options and warrants. For convertible debt and convertible preferred stock, the standard approach is the if-converted method:
- Assume the convertible security is converted into common shares at the stated conversion ratio.
- Add the resulting shares to the diluted share count.
- For diluted EPS purposes, also add back the interest expense (net of tax) on the convertible debt to net income, since if the debt is converted, those interest payments would no longer exist.
In valuation, you need to decide whether to include convertible securities in the diluted share count or treat them as debt in the enterprise value bridge. The standard approach depends on whether the convertible is in the money (conversion value exceeds par value of the debt). For more on how this fits together, see our enterprise value vs. equity value guide.
TSM in a DCF: A Special Case
When using the treasury stock method at the end of a DCF model, there is a circular reference problem. The implied share price depends on diluted shares, but diluted shares depend on the share price (because you need the share price to determine which options are in the money and to calculate the buyback). In practice, you can either use the current market price as a proxy or iterate to solve the circularity. Most bankers use the current share price for simplicity.
Common Interview Questions
Here are the most common TSM interview questions and how to answer them:
“Walk me through the treasury stock method.”: Use the step-by-step framework above. Start with “The treasury stock method calculates the net dilution from in-the-money options and warrants. You assume all in-the-money options are exercised, creating new shares. The company receives the exercise proceeds and uses them to repurchase shares at the current price. The net dilution is the difference between shares created and shares repurchased.”
“What happens to diluted shares if the stock price increases?”: Diluted shares increase because the options become more in the money. A higher stock price means the buyback can repurchase fewer shares relative to the shares created, so net dilution goes up.
“What happens if the stock price falls below the exercise price?”: The options become out of the money and are excluded from the diluted share count entirely. No rational option holder would exercise at a loss.
“Why do you use diluted shares instead of basic shares?”: Because option holders and warrant holders have a claim on the company’s equity. Using basic shares would overstate the value per share by ignoring these claims.
For a full list of technical questions you might face, download our technical cheatsheet and review our interview prep guide.
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Related Articles
- Diluted Shares Outstanding: How to Calculate Them
- Enterprise Value vs Equity Value
- Equity Value Bridge to Enterprise Value
- Walk Me Through a DCF
- How to Prepare for Investment Banking Interviews
- How the Three Financial Statements Link Together
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