If your biggest customerleft tomorrow, would you survive?

How exposed your business is to losing its biggest customers. You paste your revenue-by-customer list, and it computes the single largest customer's share of revenue, your top-five share, and a 0–100 safety score, then returns DIVERSIFIED, CONCENTRATED, or DANGER. Add your monthly cost base and it also runs a survival test: would you still clear break-even if your #1 customer walked? It grades a revenue mix, not a person, and connects to nothing.

Because the percentages aren't the whole story — survivability is. The score reflects how concentrated the book looks; the survival gate reflects whether you could absorb the loss. The shipped Consultancy sample has a 28% top customer, which scores in the CONCENTRATED band (51) — but its cost base means losing that anchor would leave it below break-even, so the gate forces DANGER. A 28% customer you can't survive losing is more dangerous than a 35% customer you can. That's the honest version of concentration risk.

The survival test is the sharp one: if you enter your monthly cost base, it checks whether the revenue left after your largest customer leaves still covers break-even. If it doesn't, that's DANGER regardless of score. If you leave the cost base blank, it falls back to a simpler rule — any single customer over 35% of revenue (the line acquirers and lenders price against) reads DANGER — and tells you it used threshold mode. The tool works with just a revenue list, but the one extra number unlocks the more honest answer.

Because it's a single point of failure on your revenue. Concentration is one of the first things acquirers and lenders stress-test — a heavily concentrated book commonly takes a material discount at sale (often cited around 20–35%) and can trigger tighter terms or a pulled credit line at renewal. It also weakens you in every negotiation with that account: when one customer can sink you, you can't walk away from a bad renewal. Fixing it before you raise, sell, or borrow is worth real money.

Revenue is what this tool reads, because it's the number everyone has and it's what concentration is conventionally measured on. But the deeper risk is margin contribution — a large, low-margin account is a different exposure than a large, high-margin one. The playbooks walk through layering margin on top once you've found your concentration. If a customer is both your biggest revenue line and your biggest profit line, that's the one to diversify away from first.

No. It's a deterministic decision aid — it computes concentration from your own numbers and flags survivability; it doesn't tell you what to do, value your business, or replace your CPA or advisor. Bring your own cost-base figure (a CPA can confirm your true break-even), and use the verdict to decide whether diversifying your customer base should move up your priority list. Not financial, investment, or accounting advice.