When a private equity fund, equity research shop, or investment bank talks about a company's earnings per share, they almost never mean basic EPS. They mean diluted EPS — and the gap between the two comes down to one concept: dilution.
What Is Dilution?
Dilution happens when a company has outstanding securities — stock options, restricted stock units (RSUs), warrants, or convertible debt and preferred stock — that could turn into new common shares. If they do, the same net income gets divided across a larger share count, which pushes EPS down. Basic EPS ignores all of this and simply divides net income by the shares currently outstanding today. Diluted EPS asks a harder question: what would EPS look like if every dilutive security that could reasonably convert into stock actually did?
The Treasury Stock Method, in Plain English
For stock options and RSUs, accountants use the treasury stock method. The logic is straightforward once you strip out the jargon: if an employee exercises an option, the company receives cash (the exercise price). The treasury stock method assumes management immediately uses that cash to buy back shares at the current market price. So the real dilution isn't the full option count — it's the net new shares left over after that hypothetical buyback.
For options, that means: Net New Shares = Options Outstanding − (Options Outstanding × Exercise Price / Current Share Price). Only in-the-money options — where the exercise price is below the current share price — are included at all; underwater options are excluded entirely, since no rational employee would exercise them.
RSUs work slightly differently because they typically carry no exercise price at all — the employee simply receives the shares once they vest. To avoid treating every unvested RSU grant as 100% dilutive, the treasury stock method substitutes the company's unrecognized (unamortized) stock compensation expense for the exercise proceeds, softening the dilution in the same spirit as the options calculation.
Convertible Securities and the If-Converted Method
Convertible bonds and convertible preferred stock are handled with a different tool: the if-converted method. Here, the question isn't "how much cash comes back," it's "would converting actually hurt EPS?" You compare the after-tax interest (or dividends) that would be avoided per new share created against the company's current EPS. If avoiding the interest costs less per share than existing EPS, conversion is dilutive and gets included; if not, the convertible is excluded from the diluted count entirely — a nuance that trips up a lot of candidates who assume every convertible security is automatically dilutive.
Why This Matters Beyond the Exam Question
Diluted share count isn't a technicality — it's the denominator that determines the equity value per share in a DCF, the EPS used in a P/E multiple, and the accretion/dilution math in an M&A model. Understating dilution makes a stock, or an acquisition, look more attractive than it really is, which is exactly why interviewers probe this topic so heavily at the Analyst and Associate level.
To see the full mechanics worked through with real numbers — treasury stock method for both options and RSUs, the if-converted test for a convertible note, and the resulting diluted EPS bridge — walk through Dilution Deep Dive, which builds a fully diluted share count and EPS figure from scratch. If you want the more foundational version of this calculation first, start with Diluted Share Count, which covers the treasury stock and if-converted methods at a more introductory level.