The Rule of 40 Explained
The Rule of 40 is the single most widely used SaaS health metric because it forces a combined view of growth and efficiency. It was popularized by Brad Feld and Don Rainey as a threshold for distinguishing healthy SaaS from businesses burning capital without justification.
The mechanics: if you grow 50% but burn 20% of revenue in FCF, you score 30 — below threshold. If you grow 30% and generate 15% FCF margin, you score 45 — healthy. If you grow 70% and break even, you score 70 — exceptional.
Find growth and FCF benchmarks by sector in the SaaS Metrics Glossary.
When Growth Beats Profitability
In low interest rate environments (2010–2021), the net present value of future cash flows was barely discounted. A dollar of revenue ten years from now was nearly as valuable as one today. In this environment, growth compounds faster than profitability expands, and the market assigns exponentially higher multiples to faster growers.
Stage also matters: at sub-$50M ARR, a company has not yet proven its business model at scale. Slowing down growth to improve FCF margins at this stage destroys option value without creating enough cash flow to compensate. High growth demonstrates product-market fit and allows the company to reach a scale where margins naturally improve through operating leverage.
See how operating leverage works in the Operating Leverage guide.
When Profitability Beats Growth
When rates rise and capital becomes scarce, investors discount future cash flows more heavily. A profitable business at 15% growth is no longer boring — it generates real cash today, requires no external financing, and can survive a market downturn without dilution.
Above $200M ARR, growth is also harder to sustain at high rates. The law of large numbers means even a fast-growing company faces natural deceleration. At this stage, a company that can generate 25% FCF margins while growing 20% is worth more (in many environments) than one growing 35% with –10% FCF.
Rule of 40 vs. EV/NTM Multiple
Research from multiple SaaS investors consistently shows that Rule of 40 score explains 60–70% of the variance in EV/Revenue multiples across public SaaS companies. The relationship is roughly:
| Rule of 40 Score | Typical EV/NTM Multiple | Examples |
|---|---|---|
| 60+ | 10x – 20x+ | Best-in-class compounders |
| 40–60 | 5x – 12x | Healthy growth SaaS |
| 20–40 | 2x – 6x | Below-threshold, improving |
| <20 | 1x – 3x | Restructuring or PE territory |
Approximate ranges; market conditions and sector expand/compress these materially.
Live FCF Margin Benchmarks by Sector
The Paths to Rule of 40 Improvement
Accelerate revenue without cost
Expansion revenue from existing customers (NRR > 100%) adds ARR without proportional S&M spend. Companies with strong expansion motion improve Rule of 40 without touching costs.
Reduce burn through efficiency
Cutting unprofitable customer segments, reducing CAC through product-led growth, or automating ops. The risk: cutting too deep slows growth and the net score falls.
Improve gross margins
Rule of 40 uses FCF margin, which is limited by gross margin. Infrastructure improvements, pricing increases, or shifting to higher-margin products improves the ceiling.