The Rule of 40 exists to answer one question: how do you compare a company growing fast and losing money against one growing slowly and making money?
Growth rate (%) + Profit margin (%) ≥ 40A company growing 60% with a −15% margin scores 45 and passes. One growing 15% with a 30% margin scores 45 and passes equally. One growing 20% with a −25% margin scores −5 and fails badly.
#Why it works
It encodes a real trade-off. Growth and profitability are substitutable in the short term — you can convert one into the other by adjusting sales and marketing spend. Cutting acquisition spend improves margin and reduces growth; increasing it does the reverse.
What the rule tests is whether the combination is efficient. A company that spends heavily and grows fast is fine. A company that spends heavily and grows slowly is not, because the spending is not converting.
#Which numbers to use
Growth rate is normally year-over-year ARR or revenue growth. Some investors use forward-looking growth; be explicit about which you mean.
Profit margin is where definitions diverge most, and the choice moves the score substantially:
- EBITDA margin — the most common in public markets
- Free cash flow margin — the most conservative, and increasingly preferred because it captures working capital and capitalised costs
- Operating margin — somewhere between
A company can score 45 on EBITDA and 28 on free cash flow if it capitalises a lot of software development. State the basis whenever you quote a score.
#Worked examples
| Company | Growth | Margin | Score | Read |
|---|---|---|---|---|
| A | 90% | −45% | 45 | Efficient hypergrowth |
| B | 45% | −5% | 40 | Balanced, on the line |
| C | 22% | 25% | 47 | Efficient at maturity |
| D | 30% | −20% | 10 | Spending without conversion |
| E | 8% | 34% | 42 | Passes, but growth is a concern |
Companies A, B and C are all healthy in different ways. Company D is the problem case: moderate growth funded by heavy losses, which is the most common failure mode in mid-stage SaaS.
Company E illustrates the rule's main weakness — it passes on profitability while barely growing, which markets typically reward with a low multiple regardless of the score.
#When it does not apply
Below roughly $10M ARR. At small scale, growth percentages are enormous and volatile — going from $1M to $2.5M is 150% growth and tells you very little. The rule produces noise. Below that scale, absolute growth and CAC payback are more informative.
During a deliberate investment year. A company that has just raised capital specifically to accelerate will fail the rule by design. That is not a warning sign if the resulting growth materialises.
Highly seasonal or usage-based businesses, where quarterly figures swing enough that any point-in-time score is unrepresentative.
#What it does not capture
The rule says nothing about retention, unit economics or market size. A company can score 50 with terrible net revenue retention by acquiring aggressively into a leaky bucket — for a while.
Always read it alongside net revenue retention and CAC payback. The SaaS metrics calculator reports all three together, because any one in isolation can be made to look good.
It also treats growth and profit as perfectly interchangeable, which markets do not. In practice, at the same score, growth is rewarded more highly than profitability at earlier stages, and the weighting shifts toward profitability as a company matures and as capital becomes more expensive.
#Using it internally
Its real value is as a planning constraint rather than a report card. When deciding next year's spend, ask what combination of growth and margin the plan produces, and whether that combination clears 40.
If the plan implies 35% growth at a −30% margin — a score of 5 — you are proposing to spend heavily for moderate growth. That is worth interrogating before the year begins rather than explaining afterwards.
Frequently asked questions
What is a good Rule of 40 score?
Above 40 is the benchmark. Above 60 is exceptional and rare. Between 20 and 40 is common for mid-stage companies and is workable if the trend is improving. Below 20 usually signals inefficient spending.
Should I use EBITDA or free cash flow margin?
Free cash flow is more conservative and harder to manipulate, and it is increasingly the preferred basis. EBITDA remains more common in public reporting. State which you used whenever you quote a score.
Does the Rule of 40 apply to early-stage startups?
Not usefully below roughly $10M ARR. Growth percentages at small scale are volatile and dominate the score. Focus on CAC payback, net revenue retention and absolute growth until the base is large enough for percentages to be meaningful.