EV/Revenue Growth-Adjusted Multiple (Rule of 40)

The Rule of 40 is a valuation shorthand that emerged from the SaaS sector to assess whether a software company’s revenue multiple is sustainable given its growth rate. It combines two numbers—annual revenue growth rate and free cash flow margin—and asks: do they sum to at least 40? If so, the valuation is plausibly justified; if not, the company is either overvalued or underinvesting in growth.

This rule sits at the intersection of growth investing and profitability discipline. Rather than treating fast-growing companies as exempt from margin scrutiny, or dismissing unprofitable growth as reckless, the Rule of 40 acknowledges a real trade-off: founders can choose to grow hard (at the expense of near-term margins) or harvest profits (at the expense of market share). The rule rewards companies that do either aggressively, and penalises those that drift in the middle.

The origins and mechanics

The Rule of 40 was popularised by Bessemer Venture Partners around 2015, though the principle predates it. The formula is straightforward:

Revenue Growth Rate (%) + Free Cash Flow Margin (%) ≥ 40

A company growing at 35% annually with a 10% FCF margin scores 45—well above the threshold. A mature software firm growing at 5% but generating 45% margins also scores 50. Conversely, a company growing at 25% but losing 30% on operations scores −5, a red flag.

The “40” itself is not magic. It is pragmatic: software companies with long-term unit economics typically need to hit 40+ to justify typical SaaS valuations (multiples in the 5–15× revenue range). Companies scoring below 40 often trade at lower multiples, or face pressure to improve one of the two drivers.

Why growth rate and margin together?

The appeal lies in honesty. A valuation multiple is ultimately a claim about future cash flows. For software companies, those flows depend on two things: how fast the top line expands, and how much of that revenue converts to cash. Neither alone tells the story. High growth with negative margins is unsustainable if the company is burning cash. Healthy margins with flat growth suggest the company has little room to justify a premium multiple.

The Rule of 40 forces a conversation: which lever are you pulling? If your company is not growing fast, are you at least very profitable? If you are in hypergrowth, investors will tolerate losses—but not indefinitely. The sum should reflect a real economic model, not blind faith.

Measurement nuances

The rule is often stated as “revenue growth + FCF margin,” but variations abound. Some analysts use operating margin instead of FCF margin, or substitute EBITDA margin. Others adjust growth rates for macro headwinds or cyclicality. These tweaks matter at the margins, but they miss the spirit: the rule is a heuristic, not a formula. It is designed to prompt thinking, not automate valuation.

One practical note: growth rates must be normalized to the market’s expectations. A 40% growth rate is meaningless in year one of a company’s life, when the base is tiny. By the time a SaaS company is large enough to trade publicly, a sustainable 40% growth rate is rare and precious. The rule works best for mid-market SaaS firms (say, $10M–$500M in annual recurring revenue), where both the growth rate and margin are real and measurable.

When the rule breaks down

Like all heuristics, the Rule of 40 has blind spots. It assumes that growth and profitability are fungible—that a founder can choose one or the other. In reality, some companies are constrained by market size, hiring capacity, or technology limits. A bootstrapped, capital-efficient software firm might score 35 not because it is mismanaged, but because it is growing into an addressable market at the fastest pace possible with available resources.

The rule also ignores unit economics. A company might score 45 on the rule and still be money-losing on a per-customer basis, if customer acquisition costs are too high. Conversely, a company with terrible unit economics might score well if it has already paid off its customer acquisition debt.

Competition and market dynamics matter too. A Rule of 40 score is meaningless if the competitive moat is eroding or if customer churn is accelerating behind the growth numbers. The rule is a starting point, not a verdict.

Practical application

For SaaS investors, the Rule of 40 functions as a screen. Companies scoring 50+ are candidates for premium valuations; those scoring 20–30 warrant scepticism; those below 20 should be examined for a clear path to 40+. Public market investors often plot portfolio companies on a growth-versus-margin chart, with 40 as the breakeven line. Private equity sponsors use it to identify “margin expansion opportunities”—mature SaaS firms that can be pushed toward 40 from the right side of the trade-off curve.

For founders and CFOs, the rule is a discipline. It prevents the trap of chasing growth at any cost while ignoring the bottom line. It also legitimizes unprofitable growth: if your company is on a path to grow at 50% next year and you are at −5% FCF margin now, the market’s patience is rational, provided you have a credible plan to move toward 40.

See also