Customer Concentration Interview Questions for PE and IB

Customer concentration is one of the fastest ways to kill or reprice a deal. Interviews want a calm framework: how concentrated, how replaceable, how contracted, and what that does to the multiple. Treat it like cliff risk plus pricing power, not a binary pass/fail slogan.

The short answer

"I look at revenue share of the top 1, top 5, and top 10 customers, then diligence contract length, termination rights, pricing power, and switching costs. High concentration is not automatic pass, but it raises risk of cliff revenue, margin pressure, and diligence on relationship dependency. I would haircut growth and/or multiple unless contracts and history say otherwise."

What to measure

Ask for cohort history, not a single-year snapshot. A logo that was 18% last year and 32% this year after a peer lost a bid is a different story than a decade-long 30% account with renewals.

Risk narrative

Thresholds without fake precision

There is no universal "bad" number. Rough interview heuristics help you sound calibrated:

• Under ~10% top customer: usually not the headline risk
• ~15% to 25%: diligence intensifies; look at contracts and margin
• ~30%+: treat as a modeled loss case before defending a premium multiple
• Top 5 above ~50% to 60%: diversification story is weak even if no single name dominates

Say the heuristic as a starting point, then pivot to quality of the revenue. A 28% mission-critical vendor with five years left and high switching costs can be cleaner than a 12% at-will account that renegotiates every quarter.

Valuation impact

Concentrated cash flows often mean:

• Lower entry multiple vs diversified peers
• More conservative debt capacity and tighter covenants
• Earnouts, holdbacks, or escrow in M&A
• Heavier QoE on revenue recognition for big accounts
• Higher working capital volatility if the big account pays slowly

Lenders and sponsors both care. In an LBO, concentration can cut leverage even when EBITDA looks stable, because downside cash flow is fatter-tailed. On the sell-side, you should still disclose and frame mitigation rather than hide the logo mix.

When concentration can be OK

• Mission-critical vendor with multi-year contract and high switching costs
• Government or blue-chip customer with renewal history and budget cycles you understand
• Diversified programs inside one logo (still diligence program-level renewal)
• Channel concentration that is industry-standard (for example, a few big retailers) if unit economics stay healthy

Still: logo risk remains. OK means underwritable with haircuts, not "ignore it."

Mini example

Revenue $100. Top customer $30. Contribution margin 40%. Fixed cost block largely stays. Losing the customer drops contribution by $12 and can drop EBITDA by nearly that if costs are sticky. At 10x, that is a huge equity story.

Walk the interviewer through the bridge: base EBITDA, loss case EBITDA, and whether you can cut variable and semi-fixed costs in twelve months. If management claims they can cut dollar-for-dollar, push for a plan. Most cost bases do not flex that cleanly.

Diligence checklist you can say out loud

1. Master service agreement and SOWs: term, auto-renew, termination for convenience, change-of-control
2. Pricing: escalators, rebates, MFN, take-or-pay or volume commitments
3. Concentration of decision makers: procurement vs end users vs founder golf buddy
4. Win/loss and RFP history with that account
5. Gross margin and collection days for the top accounts vs the long tail
6. Pipeline to diversify: named targets, cycle time, hit rates

Interview traps

1. Saying "concentration is bad" with no framework
2. Treating percent of revenue as the only metric
3. Ignoring margin mix (a low-margin whale can be worse than a smaller high-margin account)
4. Assuming a multi-year contract means zero risk (termination rights and non-renewal still matter)
5. Accepting CIM growth while the plan quietly depends on the same logo expanding

Interview verbal

"Concentration is a cliff-risk and pricing-power question. I quantify top accounts, read contracts, test relationship dependency, and run a loss or reprice case before I accept the CIM multiple. If the top customer is 30%, I want explicit downside and a path to diversify, not vibes."

Related asks

Pair with How to Read a CIM and Operating Diligence KPIs. For deal process context, also skim What Is a CIM.