What is the 'Rule of X' in SaaS?

For nearly a decade, the Rule of 40 was the unchallenged gold standard for SaaS health. It stated simply that if you added your annual revenue growth rate (as a percentage) to your profit margin (as a percentage), the sum should equal 40 or higher.

This was an elegant, simple heuristic that guided thousands of board meetings. It told founders that it was okay to lose money (-10% margin) as long as they were growing fast enough (50% growth) to compensate. Alternatively, if growth slowed to 10%, they needed to be highly profitable (30% margin).

However, as the SaaS market matured and data sets grew, Bessemer Venture Partners (BVP) noticed a flaw. The linear formula of the Rule of 40 assumes that 1% of growth is exactly equal in value to 1% of extra profit. In the real world of software investing, this is demonstrably false. A company growing at 100% with -60% margins (Rule of 40 Score: 40) is almost always valued significantly higher than a mature company growing at 10% with 30% margins (Rule of 40 Score: 40).

Why? Because growth compounds. Profit does not. A company growing at 100% will double in size next year, creating a massive base for future cash flows. A company printing cash but not growing is essentially a bond—safe, but with capped upside. The Rule of X was created to fix this valuation disconnect.

The Rule of X Formula Explained

Let's break down the components to understand why this shift is so powerful for founders and CFOs. The "X" in the Rule of X represents the multiplier applied to the growth rate.

In neutral market conditions, Bessemer suggests a multiplier of roughly 2x to 2.5x. This means that if you can accelerate your growth rate by just 1%, you can afford to burn an extra 2.5% of margin and still maintain the same valuation score. This incentivizes aggressive investment in Sales and Marketing, provided your unit economics are sound.

Why the Market Changed its Mind

BVP (Bessemer) analyzed the correlation between these metrics and enterprise value (EV/Revenue multiples) across the BVP Nasdaq Emerging Cloud Index. They found that the classic Rule of 40 had a correlation coefficient of roughly 0.54 with valuation. This is decent—it means there is a relationship—but it's messy and noisy. There were plenty of companies with high Rule of 40 scores but low valuations, and vice versa.

When they applied the Rule of X (weighting growth heavily), the correlation jumped to nearly 0.70. This is a massive statistical improvement. It simply proves mathematically what the best investors intuitively knew: Growth is the primary driver of enterprise value in software.

Investors are willing to pay a premium for growth because software markets tend to be "Winner Take Most". The company that captures the market share first builds a moat of switching costs and network effects that is incredibly hard to displace. Therefore, sacrificing near-term profit to win the market is a rational, value-maximizing strategy.

When to use which Rule? (Stage Analysis)

Not every company should be measured by the Rule of X. Using it too early or too late can lead to disastrous decision-making. Here is a guide on when to apply this advanced metric.

Ultimately, metrics are map coordinates, not the terrain. The Rule of X helps you understand if you are trading $1 of burn for enough future equity value. If your multiplier is low, you should focus on profitability. If your multiplier (valuation) is high, you should focus on capturing market share.

The Impact of Free Cash Flow (FCF)

It is important to note that the Rule of X uses FCF Margin, not EBITDA. EBITDA is an accounting fiction that can hide all sorts of sins (like capitalized software development costs). Free Cash Flow is the actual cash entering or leaving your bank account.

Bessemer chose FCF because it is truth. You cannot pay salaries with EBITDA. You can only pay them with cash. By linking growth to FCF, the Rule of X forces founders to be honest about the cash consumptiveness of their growth. If you are growing 100% but your FCF margin is -200%, your Rule of X score is still negative (Assuming 2.5x multiplier: 250 - 200 = 50... wait, actually that's a good score).

Correction: If you grow 100% with -200% margin, your score is 50. But that level of burn is likely unsustainable for other reasons (runway). The rule assumes you have the cash balance to survive.

Real World Case Study: Datadog vs. ZoomInfo

To understand the Rule of X in action, let's look at two elite SaaS companies from 2021-2022. Both were trading at premium multiples, but for different reasons.

This case study illustrates why CFOs chase the Rule of X. It aligns internal incentives with external market valuation drivers.

Frequently Asked Questions

Disclaimer: This content is for educational purposes only and does not constitute financial or legal advice. Consult a professional before making business decisions.