The Rule of 40 formula
The Rule of 40 adds revenue growth rate to profit margin percentage. A score at or above 40 indicates a balanced, healthy SaaS business.``` Rule of 40 Score = Revenue Growth Rate % + Profit Margin % ```
Both components cover the same period, typically the trailing twelve months or the most recently completed fiscal year.
Examples with different growth-profitability mixes:
| Revenue growth | Profit margin | Rule of 40 score |
|---|---|---|
| 50% | -5% | 45 (passes) |
| 30% | 12% | 42 (passes) |
| 20% | 5% | 25 (fails) |
| 15% | 28% | 43 (passes) |
Why FCF margin beats EBITDA for this metric
EBITDA excludes stock-based compensation, which is a real economic cost in SaaS businesses where equity is a primary compensation tool. It also excludes the cash consumed by working capital cycles and capitalized R&D, both of which affect real cash generation.
Free cash flow margin captures all of these. The formula using FCF:
``` Rule of 40 Score = Revenue Growth Rate % + (Free Cash Flow / Revenue) % ```
FCF-based scores are harder to inflate through accounting choices and are more comparable across companies with different compensation structures.
Calculating revenue growth rate correctly
Growth rate for the Rule of 40 is typically year-over-year revenue growth. The numerator is the change in revenue from the prior-year period; the denominator is the prior-year revenue.
``` Revenue Growth Rate = (Current Revenue - Prior Year Revenue) / Prior Year Revenue ```
Use GAAP revenue, not ARR or bookings, when computing the Rule of 40 for external reporting. ARR can be used internally but creates comparability problems when benchmarking against public company disclosures that use recognized revenue.
Limitations
The Rule of 40 is a summary metric, and summary metrics compress information. A score of 40 achieved via very high growth and deeply negative margins carries different risk than the same score achieved via moderate growth and strong profitability. Investors increasingly prefer the profitable path, particularly in higher-rate environments.
Pair the Rule of 40 with burn multiple and quick ratio to build a complete SaaS efficiency picture. Each adds what the others miss: burn multiple shows cash consumption, quick ratio shows ARR quality, and the Rule of 40 ties growth to profitability in one score.
For the broader definition and context, see rule of 40.
Frequently Asked Questions
What is the Rule of 40 formula?
Rule of 40 equals revenue growth rate percentage plus profit margin percentage. A company growing at 30% with a 15% FCF margin scores 45, which clears the 40 threshold. A company growing at 60% with a negative 25% FCF margin scores 35, which falls below it despite strong topline growth.
Should you use EBITDA margin or free cash flow margin for Rule of 40?
Free cash flow margin is the more reliable input. EBITDA excludes stock-based compensation, capitalized software development costs, and working capital movements that significantly affect cash generation in SaaS businesses. FCF margin reflects what the company actually produces in cash and cannot be improved by accounting choices.
Is Rule of 40 useful at all stages of growth?
It is most useful from Series B onward, when investors begin evaluating the balance between growth and capital consumption. Early-stage companies often have very high growth rates and deeply negative margins, and the formula does not meaningfully differentiate them. At growth stage and above, the Rule of 40 is a standard board metric alongside ARR growth and net revenue retention.
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