The SaaS growth-versus-profit heuristic VCs use to score health at a glance — with the original Brad Feld math, the Bessemer benchmark data, and why solo SaaS founders should mostly ignore it.
Research-based overview. This article synthesizes Brad Feld’s original 2015 post defining the rule, the Bessemer Cloud Index benchmark data, and public reporting from SaaS Capital, OpenView, and quarterly earnings disclosures across the public SaaS cohort. How we research.
The Rule of 40 is the closest thing the SaaS investing world has to a universal scoreboard. It was coined by venture capitalist Brad Feld in a February 2015 post on his blog, where he summarized a piece of investor folk wisdom he had been hearing in board meetings: a SaaS company’s growth rate plus its profit margin should sum to at least 40. The framing was deliberately rough — a back-of-envelope rule, not a model — but it stuck. By 2018 it was standard vocabulary inside every SaaS-focused venture firm. Bessemer Venture Partners now publishes Rule of 40 scores quarterly in their Cloud Index alongside ARR multiples and net retention.
For solo SaaS founders building products today, the Rule of 40 shows up in two contexts: as a vocabulary item that comes up in pitch conversations and SaaS Twitter, and as a number that someone occasionally tells you that you should be hitting. Most of the time, neither of those contexts applies to a sub-$1M-ARR solo SaaS — the rule was designed for a different audience and a different scale. But it is worth knowing precisely because the spread of contexts where it does and does not apply is part of being literate about SaaS economics.
The math is deliberately simple:
Both inputs are percentages of the same time period (a year). Both can be negative. The sum is your “Rule of 40 score.” A company at 40 or above is healthy by the rule; below, the rule is signaling either growth is too inefficient or profitability is too thin given the growth rate.
The rule is easiest to internalize with concrete combinations of growth and margin:
| SaaS company | Revenue growth | Profit margin | R40 score | Verdict |
|---|---|---|---|---|
| SaaS A (growth-stage, burning cash) | 60% | -25% | 35 | Below the rule — growth is real, but they are buying it too expensively. |
| SaaS B (efficient mid-stage) | 30% | +15% | 45 | Above the rule — balanced trade between growth and profit. |
| SaaS C (hypergrowth phase) | 100% | -55% | 45 | Above the rule — growth is doing the heavy lifting; burn is justified. |
| SaaS D (bootstrapped, profitable) | 30% | +40% | 70 | Well above the rule — the bootstrapped-SaaS sweet spot. |
| SaaS E (slow growth, thin profit) | 15% | +10% | 25 | Below the rule — neither growing fast enough nor profitable enough. |
The pattern the rule captures: there are many paths to a healthy SaaS. Burning cash to grow fast is one path. Modest growth with strong margins is another. What the rule penalizes is the middle — growing slowly while not making much money — which is the most common failure mode for SaaS companies that scaled their team and cost base ahead of their revenue.
The Rule of 40 was originally framed around EBITDA margin (earnings before interest, taxes, depreciation, and amortization, divided by revenue). Brad Feld’s 2015 post used EBITDA, and that has stuck as the default for private-company conversations. But the practice has drifted in several directions, and you will see all of these used as the “profit” input depending on who is talking:
The pragmatic guidance: pick the metric your audience uses. Venture board conversations default to EBITDA. Public-market investors default to FCF margin. If you are comparing companies, normalize to the same denominator or the comparison is meaningless.
The Rule of 40 became standard because it solves a real problem for investors evaluating SaaS companies at scale: SaaS valuations have historically been driven by revenue growth, but growth without profitability eventually becomes a liability. A pure revenue-multiple model rewards burning more cash to grow faster, indefinitely. The Rule of 40 introduces a counterweight: at a given growth rate, how profitable does the business need to be to be considered healthy?
Bessemer’s Cloud Index tracks the public SaaS cohort and consistently shows a correlation between Rule of 40 score and enterprise-value-to-revenue multiple. Best-in-class public SaaS companies score 60 or higher on Rule of 40; the index median floats in the 30 to 40 range depending on macro conditions; the bottom quartile sits below 25. Investors use the score as one of three or four headline screens for whether a company is worth deeper diligence.
The rule is also useful for ongoing board conversations, where it gives directors and executives a shared shorthand for the growth-versus-burn trade-off. “We’re at 35 now, the plan needs to get us to 50 by end of next year” is a sentence that means something specific to a SaaS operator.
The base rule has spawned a family of related heuristics:
The proliferation tells you something: the Rule of 40 is a useful rule of thumb, not a load-bearing financial model. Every variant exists because someone tried to apply the base rule to a context where it did not fit and built a tweak. The base rule remains the most-cited.
The rule was designed for a specific kind of company: a mid-to-late-stage SaaS at $10M+ ARR with predictable growth, a real cost base, and a credible path to either profitability or exit. It does not apply cleanly outside that context.
Solo SaaS economics look nothing like the cohort the rule was designed for. A solo founder running a $5K MRR SaaS typically has 70 to 80 percent gross margins (high), is growing at variable rates depending on whether they pushed a marketing campaign that week (lumpy), and pays themselves a founder salary that may or may not be counted as “profit” depending on accounting. Plug those numbers into Rule of 40 and the score is mostly noise. A $5K MRR SaaS with 100% YoY growth and a -200% margin (because the founder is paying themselves $10K/month from outside savings) scores -100 by Rule of 40, which is not telling you anything useful about the underlying business.
Even venture-backed SaaS pre-Series-B has Rule of 40 scores that bounce around quarter to quarter based on hiring decisions and one-time expenses. The rule becomes more useful past $10M ARR, when the cost base is mature enough that quarterly numbers reflect underlying economics rather than noise.
A bootstrapped SaaS at 30% growth and 40% margins scores 70 on Rule of 40 — a number that would have a venture investor calling weekly. But VC investors do not care, because there is no exit math: a profitable, slow-growing private SaaS without venture financing is not a venture asset class. The Rule of 40 gives you a healthy-business signal that does not map onto venture-return expectations. Bootstrappers should optimize for what makes them happy as operators; Rule of 40 is a fine internal target but a bad north star.
The Rule of 40 was designed for the era of 80% SaaS gross margins. AI SaaS — products that resell GPT, Claude, or other foundation-model tokens with a UI wrapped around them — has structurally lower gross margins. A product that bills $30/month per user but spends $12 on inference for the average user has a 60% gross margin, not 80%. Every percentage point of gross-margin compression eats directly into the profit-margin input of Rule of 40, which makes AI SaaS look worse on the rule than equivalent classical SaaS even when the underlying business is healthy. Some investors are starting to apply a modified Rule of 40 to AI-margin SaaS; the consensus has not landed. The true cost of running an AI SaaS goes deep on the margin math.
The other heuristic frequently mentioned in the same breath is the Magic Number, which measures sales-and-marketing efficiency. The Magic Number is calculated as the change in quarterly subscription revenue, annualized, divided by the prior quarter’s sales-and-marketing spend. A score above 1.0 is healthy; above 1.5 is strong.
The two metrics are complementary, not competing:
A SaaS can hit Rule of 40 while having a poor Magic Number if other parts of the cost base are efficient. A SaaS can have a great Magic Number but fail Rule of 40 if R&D or G&A spend is bloated. Investors look at both; the two together give a better picture than either alone.
If Rule of 40 is the wrong scoreboard for a solo SaaS founder, what is the right one? The honest answer is that the metrics that matter shift dramatically with scale:
The metrics that matter most through the $0-10M ARR journey are covered at length in SaaS metrics that matter. The foundational definitions show up across what is MRR, what is ARR, what is ACV, and what is churn rate.
Strip away the formula and the rule is asking one question: are you trading growth for profitability at the right rate?
If you are below 40, one of two things is true:
If you are above 40, the rule is saying the trade-off is in the healthy zone. That does not necessarily mean you are doing everything right — you might be hitting 50 by underinvesting in growth and missing a market window — but the trade is reasonable on average.
The Bessemer benchmark numbers from the Cloud Index give rough public-SaaS calibration: best-in-class score 60+, median scores 30 to 40 depending on macro conditions, bottom quartile sits below 25. These bands have moved with the market — in low-interest-rate environments investors tolerated lower scores in exchange for higher growth; in higher-rate environments, the bar moves up because cash profitability gets more valuable in absolute terms.
The Rule of 40 is a useful piece of SaaS literacy and a poor scoreboard for solo founders. It was designed for mid-to-late-stage venture-backed companies with mature cost bases, and the underlying signal it captures — the trade between growth and profitability — only becomes meaningful at the scale where both numbers are stable enough to compare. For a $5K MRR side project, plugging numbers into the formula produces a result that says nothing useful about the business.
That said, the underlying intuition is good: growth is not free, profitability is not free, and a healthy SaaS finds a balance between them that scales. As your product moves from product-market fit into the hiring-and-scaling phase, the Rule of 40 graduates from vocabulary item to useful target. Until then, the metrics that actually move are MRR, churn, NRR, and the gross margin math that AI SaaS makes inescapable. Pricing strategy — covered in the complete guide to SaaS pricing — is the lever that moves all of those at once.
The stack, prompts, pricing, and mistakes to avoid — for solo founders building with AI.