What the Rule of 40 Calculates and When It Applies

The Rule of 40 is calculated by adding the revenue growth rate as a percentage to the EBITDA margin or free cash flow margin as a percentage. A SaaS business growing at 60% with a negative 15% EBITDA margin scores 45, which passes the test. A business growing at 20% with a 10% EBITDA margin scores 30, which does not. The rule is used by investors to evaluate whether a company's combination of growth and profitability is sufficient at its current stage and capital efficiency.

The Distinction That Matters

The Rule of 40 rewards either speed or efficiency. It does not reward both simultaneously — it requires the sum of the two to exceed 40, which allows a company to be highly unprofitable if it is growing very fast, or slow-growing if it is highly profitable. The trap is treating it as a binary pass or fail test rather than as a benchmark that varies by stage. A pre-Series A company is not expected to score above 40. A post-Series B company is. Using the same benchmark across different stages produces misleading comparisons, and using it to defend high losses at low growth rates produces the worst possible interpretation of the metric.

Which margin to use also matters: investors in some sectors calculate it on EBITDA, others on free cash flow. The calculation in the financial model must match the methodology the specific investor uses or the comparison will not be meaningful.

Why It Surfaces in a Raise Process

In a Series A or Series B process, investors will calculate the Rule of 40 from the financial model before discussing growth efficiency. A company whose financial model does not contain an EBITDA calculation, or whose management accounts do not separate EBITDA from net income, cannot produce this figure without reconstruction. Investors who ask for it and receive a blank are not encountering a gap in the metric — they are encountering a gap in the financial infrastructure that should have been in place before the raise began.

The Common Structural Error

The most common error is using net income margin instead of EBITDA margin. Net income includes interest, tax, depreciation, and amortisation, which EBITDA explicitly excludes. Using net income instead of EBITDA produces a lower margin figure in most early stage businesses, depressing the Rule of 40 score and making the company appear less efficient than the standard benchmark calculation would show.

RELATED TERMS
- How Net Revenue Retention Is Calculated Correctly
- What the Burn Multiple Tells Investors About Capital Efficiency
- How Gross Margin Is Calculated for a SaaS Business
- The Investor Data Room as a Signal of Operational Maturity

Tool: Startup Financial Readiness Scorecard