Rule of 40 for SaaS Explained
In Finance startups on Bowora
The Rule of 40 is a SaaS efficiency heuristic: revenue growth rate (%) plus profit margin (%) should sum to at least 40. It is a shorthand investors use to discuss growth versus profitability tradeoffs—not a pass/fail law for every startup stage. Core metric definitions sit in the Startup Metrics hub; retention context appears in NRR vs churn.
The formula (as commonly stated)
Rule of 40 score = revenue growth rate % + profit margin %
Illustrative example only: 25% year-over-year growth + 20% EBITDA margin = 45. Definitions of "profit margin" vary (EBITDA, operating margin, free cash flow margin)—always state yours.
What it is useful for
- Comparing mature-ish subscription businesses on a single efficiency axis.
- Framing board conversations when growth slows but margins improve (or vice versa).
- Pairing with retention metrics—NRR above 100% can support growth with less new-logo pressure.
What it is not
- A seed-stage requirement—early companies often sacrifice margin for product-market fit.
- A substitute for CAC payback, runway, or cohort retention.
- A reason to invent margin numbers you cannot defend in diligence.
Related metrics to show alongside Rule of 40
- MRR / ARR growth with explicit labeling.
- LTV:CAC with gross margin in the LTV calculation.
- NRR for expansion versus churn in the installed base.
Practitioner framing appears in resources such as Bessemer State of the Cloud. Use the rule as conversation context, not as a vanity slide bullet without definitions.
FAQ
- What is the Rule of 40?
- A common SaaS heuristic: revenue growth rate percentage plus profit margin percentage should sum to at least 40. Definitions of margin vary—state yours.
- Does the Rule of 40 apply at seed stage?
- Usually not as a requirement. Early companies often trade margin for learning. Use it as mature-efficiency context, not a seed gate.
- What metrics pair with Rule of 40?
- Show labeled MRR/ARR growth, gross-margin-aware LTV:CAC, CAC payback, and NRR or churn with clear cohort definitions.
