Your Win-Rate Might Be Fooling You
It’s very likely that your win-rate—and a few other comforting ratios—are lying to your face.
I’ve been reading about mathematical thinking. Yes, the math can be dense, but to my surprise, it has its own cliffhangers. Had Aristotle not timed the swinging cycle of a candelabra while at church, we wouldn’t have one of today’s finest pieces of machinery—the automatic wristwatch. Had we not discovered the ellipse, we might still believe that Mars occasionally decides to moonwalk across the sky. Sorry, horoscope lovers Mars retrograde isn’t a thing.
And last but not least—realizing how easily percentages can be manipulated, and how disastrous the outcomes can be. Because many of us, though we pretend to be rational beings, fail to apply mathematical thinking to our daily lives.
The UK Pill Scare That Wasn’t
According to How Not to Be Wrong: The Power of Mathematical Thinking by Jordan Ellenberg, in 1995 the UK Committee on Safety of Medicines issued a public warning—widely amplified by the media— that third-generation oral contraceptive pills doubled the risk of life-threatening blood clots. (Yes, a 100% increase.)
As a result, many women stopped taking their contraceptives. A survey later found that 40% of unplanned pregnancies were among women who had stopped after the announcement. What the warning failed to mention? The risk went from 1 in every 7,000 women (0.01%) to 2 in every 7,000 (0.02%). Mathematically true—but catastrophically misleading.
From Birth Control to Pipeline Control
While misreading your win-rate might not cause a public health crisis, it can cause a financial one—personal, corporate, or (most likely) both. And the problem is far more widespread than you think. Even CRMs get it wrong.
Gold Medal for Bad Math: HubSpot
HubSpot’s default win-rate formula divides won business by the sum of won + lost business. Which makes me wonder: Has anyone at HubSpot ever actually worked in sales—or passed high-school math?
Here’s why that’s nonsense:
Most salespeople never mark deals as closed-lost. (Hope never dies, right?)
That means the formula ignores all open deals—usually the largest chunk of your pipeline.
The result? A wildly inflated win-rate that looks great on dashboards and terrible in boardrooms.
Should you use HubSpot’s win-rate for planning or forecasting? Absolutely not. Maybe as a warning of how not to calculate win-rate. Perhaps that was their master plan all along. The baseball equivalent would be calculating a batting average by counting only hits and outs—while ignoring strikeouts. That fourth at-bat might not be as impressive as you think.
Unless you have a very short sales cycle and a team of monks disciplined enough to close every deal properly, that number is meaningless. Sure, maybe the math checks out—in the limit as t → ∞. I know, hilarious.
Silver Medal: Timeframe Confusion
The runner-up mistake? Using won business in a given month divided by total pipeline, without defining a timeframe. Sure, at least the denominator isn’t just won plus lost business. But win-rates without a clear timeframe are like horoscopes—vaguely comforting, empirically useless.
A close tie for silver:
When you calculate won business this month (regardless of creation date) divided by pipeline created this month. That also overestimates your win-rate—because you’re borrowing wins from previous months and comparing them against fresh opportunities.
Bronze Medal: Premature Calculation
If your sales cycle is 30 days, you can’t compare the current month win-rate to previous month and call it settled. It won’t stabilize until 30 days after the month ends. Unless you’re a decorated psychic, you need full cycles to calculate a valid win-rate. Otherwise, you’re just using random numbers to make business decisions. All in on one black, might as well!
The Pure Win-Rate
For the past seven years—ever since I finally reached win-rate maturity—I’ve used what I call the purest win-rate calculation, almost as elegant as E = mc²:
I also make it a point to tell stakeholders—CEO, board, investors—whether I’m sharing a trend (early in the cycle) or a settled win-rate.
The Real Math of Sales
Unless your business fundamentals truly demand a different definition, any deviation from this formula means you’re doing reporting gymnastics—not business analysis. Remember: every at-bat counts. Ignore the strikeouts, and sure—your batting average looks pretty. But you’ll miss your forecast, underestimate your customer acquisition costs, and, get traded to the Colorado Rockies.