The Rule of 40 is a quick diagnostic for SaaS business health. Add the company's annualised revenue growth rate (as a percentage) to its EBITDA or free cash flow margin (as a percentage). If the sum exceeds 40, the business is operating within an acceptable efficiency range. A company growing at 60% with a -20% margin scores 40. A company growing at 20% with a 20% margin also scores 40 — they are just at different stages of the maturity curve.
The Rule of 40 is most useful as a benchmark for investors evaluating public or late-stage SaaS companies, where both growth rate and profitability are knowable. For early-stage startups, the metric is less directly applicable — a seed-stage company with 200% growth and -150% margins scores 50, but that math only makes sense in the context of the investment needed to sustain 200% growth. The Rule of 40 becomes a genuine operating constraint from Series B onward.
Critically, the Rule of 40 is not a hard rule — it is a heuristic. Some exceptional growth businesses score below 40 and are still excellent investments; some mature SaaS companies score 60+ because they've stopped investing in growth. The metric should be contextualised with the company's stage, the quality of its revenue, its retention profile, and the competitive landscape. Presenting a Rule of 40 score without these caveats in a pitch invites scrutiny rather than credibility.