When one company announces it is acquiring another, one of the first questions analysts and investors ask is whether the deal will be accretive or dilutive to the acquirer's earnings per share (EPS). It's one of the most common concepts tested in M&A interviews, and it's also one that's easy to memorize as a formula without actually understanding what's driving it.
The Basic Definitions
A deal is accretive when the acquirer's pro forma EPS (its combined EPS after the deal closes) is higher than its standalone EPS before the deal. A deal is dilutive when pro forma EPS ends up lower. Nothing more mysterious than that — it's a before-and-after comparison of one number, earnings per share.
The confusing part for most candidates isn't the definition, it's understanding why a deal ends up accretive or dilutive in the first place, especially for an all-stock transaction where no cash or debt changes hands.
Why the Acquirer's P/E Multiple Is the Real Driver
In a 100% stock deal, the acquirer isn't spending cash — it's issuing new shares of itself to pay for the target. That means the real question is: how many earnings does the acquirer get from the target, versus how many new shares does it have to hand out to get them?
The shortcut most bankers use: compare the effective P/E multiple the acquirer pays for the target's earnings (the offer price divided by the target's EPS) to the acquirer's own trading P/E multiple. If the acquirer is paying a lower multiple than its own stock trades at, the deal is accretive — it is effectively buying a dollar of earnings for less than the market is currently willing to pay for a dollar of the acquirer's own earnings. If it pays a higher multiple, the deal is dilutive.
This is why acquirers with richly valued stock (a high P/E) have a structural advantage in stock-funded M&A: almost anything they buy at a lower multiple than their own will mechanically boost EPS, regardless of whether the underlying business is actually a good fit.
A Worked Example
Take an acquirer trading at a 20.0x P/E buying a target at an effective 12.0x P/E (after paying a premium to the target's pre-deal share price). Combining the two companies' net income and dividing by the new, larger share count produces a pro forma EPS that's higher than the acquirer's standalone EPS — an accretive deal, purely because of the multiple gap. The full numbers, including the exact exchange ratio, share count, and break-even math, are walked through step by step in our Accretion/Dilution: The Basic Concept case study.
Why This Matters Beyond the EPS Math
Accretion/dilution is a screening tool, not a verdict on deal quality. A deal can be EPS-accretive on day one simply because of the multiple arbitrage above, even if the acquirer overpays strategically or the target is a weak business. Conversely, a dilutive deal can still create real value if it buys high-growth assets at a fair price — the near-term EPS drag can be more than offset over time. That's part of the reason M&A processes exist in the first place: to figure out why a company is doing a deal, not just whether the deal moves one accounting metric. For more on the motivations behind M&A generally, see What Is M&A and Why Do Companies Do It? and how buyer type shapes the numbers in Types of Buyers: Strategic, Private Equity, and Family Office.
Key Takeaways
Accretion/dilution compares pro forma EPS to the acquirer's standalone EPS. In an all-stock deal, the outcome is driven mainly by the gap between the acquirer's own P/E multiple and the effective multiple it pays for the target. It's a useful first screen, but it says nothing on its own about whether a deal creates real economic value — that requires looking at synergies, financing, and returns versus cost of capital.