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Rule of 40

Updated Jun 24, 2026 at 8:22pm

Research Draft High 1,109 words

The Rule of 40 is a back-of-envelope health check for subscription-software (SaaS) companies: a company's annual revenue growth rate plus its profit margin should sum to 40% or more. Its entire value is in capturing one tension in a single number — the trade-off between growth and profitability. A company can legitimately reach 40 by growing fast while burning cash (e.g. 60% growth, −20% margin) or by growing modestly while throwing off cash (e.g. 15% growth, 25% margin). The heuristic says the combination is what signals a durable business, and that overweighting either dimension at the total's expense is a warning sign. It is a screening tool and a rough valuation proxy, not a precise model.

How it's calculated

Rule of 40 score = Revenue growth rate (%) + Profit margin (%)

The catch — and the source of most confusion — is that neither input has a standardized definition, so two analysts can compute very different scores for the same company.

  • Growth rate: usually year-over-year revenue growth. Private SaaS firms often use ARR/MRR growth; public companies typically use reported (often GAAP) revenue growth, which can lag ARR.
  • Profit margin: this is where definitions diverge. Common choices are EBITDA margin, free cash flow (FCF) margin, operating margin, or net margin. McKinsey notes that for larger software companies, LTM (last-twelve-month) FCF margin is the profitability measure most watched and most correlated with valuation (McKinsey). Early-stage analyses often default to EBITDA or FCF because GAAP net income is distorted by stock-based compensation and deferred-revenue accounting.

Worked example: 25% revenue growth + 18% FCF margin = score of 43 (passes). 45% growth + −10% FCF margin = 35 (fails, despite faster growth). Because the margin can be negative, a high-growth pre-profit startup can still clear 40 if growth is strong enough.

How it's used in practice

In SaaS investing and operating, the Rule of 40 serves three roles:

1. A screen. Investors filter a universe of software names, treating ≥40 as "above the line" and worth deeper diligence. It quickly flags companies that are growing fast but burning unsustainably, or profitable but stagnating. 2. A board / management KPI. Operators use it to frame the central capital-allocation question: should the next marginal dollar fund growth (sales, R&D) or fall to margin? The rule reminds teams that sacrificing one to juice the other doesn't improve the underlying score. 3. A valuation heuristic. Empirically, software companies above 40 have tended to command higher EV/Revenue multiples, so the score is used as a shorthand proxy for "should this trade at a premium multiple."

Origin: the term was popularized by VC Brad Feld in a February 2015 post, "The Rule of 40% for a Healthy SaaS Company," in which he credited a late-stage investor at a board meeting; Fred Wilson voiced similar thinking around the same time (Wikipedia, Wall Street Prep).

Adoption, debate & evidence

The Rule of 40 is one of the most widely cited metrics in SaaS, but the honest picture is more measured than the folklore.

  • The 40 threshold is arbitrary. SaaS Capital, which surveys 1,000+ SaaS companies, states the 40% figure is "completely arbitrary" and notes plenty of value-creating businesses operate below it. Their data puts the median growth-plus-profit ratio in the 20–35% range — meaning the typical SaaS company does not actually clear 40 (SaaS Capital).
  • Few companies sustain it. McKinsey's analysis of 200+ software companies (2011–2021) found firms exceeded Rule-of-40 performance only about 16% of the time, and only roughly a third hit it in any given year (McKinsey). Sustained outperformance is rare and is what actually correlates with premium value.
  • Growth and profit are not equally valued — the rule's core assumption is wrong. The Rule of 40 trades growth and margin dollar-for-dollar, but markets don't. Bessemer Venture Partners' Rule of X (2024) applies a multiplier (~2x private, ~2–3x public) to growth because "a margin increase has a linear impact on value, while a growth-rate increase can have a compounding impact." Bessemer reports the Rule of X explains ~62% of the variation in valuation multiples (R²) versus ~50% for the Rule of 40 (Bessemer). That an R² of ~0.50 is the baseline tells you the Rule of 40 has real but modest explanatory power over valuation.
  • Behavior shifts with scale. SaaS Capital's data shows larger companies ($50M+ ARR) cluster toward profitability (e.g. ~10% growth, 20–30% margin), so the same score means different things at different stages.

Strengths & limitations

Strengths. It is fast, intuitive, and forces the growth-vs-profit trade-off into one comparable figure. As a directional screen — flagging cash-burning hyper-growth or profitable stagnation — it is genuinely useful, and "above 40 over multiple years" does carry real signal about durability and valuation.

Limitations.

  • No standard inputs. Mixing EBITDA, FCF, and net margin, or ARR vs GAAP growth, makes cross-company comparisons unreliable unless inputs are normalized. Always confirm which margin is used.
  • Equal weighting is empirically wrong — growth deserves a premium (the Rule-of-X critique).
  • Stage- and size-blind. A 40 at $10M ARR (50% growth, −10% margin) is a very different animal than a 40 at $1B ARR (15% growth, 25% margin); the rule treats them identically.
  • Gameable / point-in-time. A one-quarter margin spike from cost cuts can lift the score without improving the business.
  • #1 misuse: treating 40 as a binary pass/fail verdict on company quality rather than as one input among many. A 38 is not "unhealthy" and a 41 is not "healthy."

Sources

Disputes flagged: (1) the 40 threshold is arbitrary and most SaaS firms fall below it; (2) the equal weighting of growth vs profit is contested — Bessemer's Rule of X argues growth should be multiplied; (3) no industry-standard profit-margin definition exists, so reported scores are not directly comparable.