When two companies merge, deal teams almost always talk about "synergies" — the extra value the combined company is expected to create that neither company could create on its own. In interviews, this term gets thrown around loosely, but a strong candidate can immediately break it into two very different categories: revenue synergies and cost synergies. Understanding the difference — and why interviewers trust one far more than the other — is one of the fastest ways to sound credible in an M&A interview.
Cost Synergies: Savings the Combined Company Controls Directly
Cost synergies come from eliminating duplicate spending once two companies combine. Typical sources include consolidating overlapping headcount (especially in back-office and corporate functions), combining procurement volumes to negotiate better supplier terms, closing redundant facilities, and retiring duplicate software or systems.
The defining feature of cost synergies is that management has direct control over whether they happen. A decision to eliminate a redundant department or renegotiate a supplier contract can be executed on a known timeline with a known outcome. That is why cost synergies are typically assigned a higher probability of realization in a deal model — often 70-80% — compared to revenue synergies.
Revenue Synergies: Upside That Depends on Customers, Not Just Management
Revenue synergies come from the combined company generating more sales than the two companies would have separately — for example, cross-selling one company's products to the other's customer base, bundling complementary products, or gaining pricing power from a larger market share.
The problem: revenue synergies depend on customer behavior, not just internal decisions. Customers may not want the bundled product, sales teams may resist learning a new portfolio, and competitors may respond aggressively to defend their own accounts. Because of that uncertainty, deal teams typically apply a much lower probability of realization to revenue synergies — often 40-60% — and interviewers expect candidates to know why.
Why the Distinction Matters for Interviews
A common interview trap is treating "synergies" as a single number. In reality, every rigorous synergy analysis keeps revenue and cost synergies separate because they behave differently in three ways: they carry different realization probabilities, they follow different timelines (cost synergies are usually front-loaded, revenue synergies ramp up more slowly as sales relationships mature), and they convert to EBITDA differently — cost synergies drop straight to the bottom line, while revenue synergies only contribute their gross margin, since the additional revenue still carries a cost to deliver.
A worked example makes this concrete. In Synergy Case: Revenue and Cost, you'll walk through exactly this split — risk-adjusting a $20m revenue synergy estimate and a $15m cost synergy estimate at different probabilities, phasing both over a three-year ramp, converting the revenue synergy to its EBITDA impact using a gross margin assumption, and discounting the combined stream back to a present value.
If you want the fuller synergy valuation methodology — including how taxes factor into the calculation — the related Synergy Valuation case builds on the same risk-adjustment and discounting logic.
How This Fits Into the Broader Deal
Synergy estimates ultimately answer one question for the acquirer: how much of a premium can we justify paying above the target's standalone value? Overstating synergies — by ignoring execution risk, skipping the phasing timeline, or forgetting the margin conversion on revenue synergies — is one of the most common ways acquirers overpay for a deal. If you're building out your broader M&A interview prep, it's worth pairing this with cases on accretion/dilution analysis and the merger consequences model, since synergy assumptions feed directly into both.