Series B is where unit economics stop being aspirational and start being existential. At Series A, investors accept that your metrics are directional. At Series B, they expect them to be defensible — and the scrutiny is only increasing in the current funding environment.
The three numbers that matter most: LTV:CAC ratio (target 3:1 minimum, but the real question is the payback period), net revenue retention (above 110% for enterprise SaaS, above 95% for SMB), and gross margin trajectory (expanding, stable, or compressing, and why).
Most Series B candidates I evaluate have a blind spot in their unit economics: they calculate CAC using marketing and sales costs but exclude the SDR team, the solution engineering time spent on trials, and the opportunity cost of founder-led sales. When you include fully loaded costs, the real CAC is often 40-60% higher than the board deck suggests.
The fix isn't just better accounting — it's better architecture. Build your attribution model to capture every cost that touches the customer acquisition journey. Track cohort economics monthly, not quarterly. And most importantly, understand which segments are actually profitable and which are subsidized by your best customers.
Series B lending decisions increasingly depend on demonstrating not just growth, but efficient growth. The companies that can show improving unit economics alongside top-line expansion are the ones that close rounds on their terms.
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