The Rule of 40 is a SaaS growth-efficiency benchmark: Revenue Growth Rate % + Profit Margin % (commonly EBITDA margin or free cash flow margin). A combined score of 40% or higher is the widely-cited "healthy" threshold. A company can hit it through fast growth, strong profitability, or a balance of both.
What is the Rule of 40?
The Rule of 40 is a rule-of-thumb benchmark used to judge whether a SaaS company's balance of growth and profitability is healthy. It states that a company's revenue growth rate, expressed as a percentage, plus its profit margin, also expressed as a percentage, should add up to 40% or more.
The appeal of the Rule of 40 is that it collapses two metrics that are often in tension, how fast you're growing, and how profitable you are, into a single number. A company doesn't need to excel at both to pass; it needs the combination to clear the bar.
Rule of 40 formula
In words: the Rule of 40 score equals your year-over-year revenue growth rate percentage plus your profit margin percentage.
Revenue growth rate is usually measured as year-over-year ARR growth. Profit margin is where companies diverge. Most commonly EBITDA margin or free cash flow margin, though operating margin and net margin also show up. Whichever margin you use, apply it consistently, since the choice changes the resulting score.
Example
Say a company is growing ARR at 30% year over year, and its EBITDA margin is 15%.
Rule of 40 score = 30% + 15% = 45%
Since 45% is above the 40% threshold, this company is considered healthy by the Rule of 40, even though neither its growth rate nor its margin alone would necessarily stand out.
Now compare a second company: growing ARR at 18% year over year, with an EBITDA margin of -5% (still burning cash).
Rule of 40 score = 18% + (-5%) = 13%
At 13%, this company falls well short of the 40% threshold. That doesn't automatically mean it's failing as a business, but it's a signal worth investigating: is growth about to accelerate, is the margin about to improve, or is neither happening. In that last case, the combination of slow growth and ongoing cash burn is a genuine warning sign.
Why the Rule of 40 matters
The Rule of 40 exists because looking at growth or profitability in isolation can be misleading. A company growing 60% year over year sounds impressive, but if it's burning cash at a rate that erases 40% of revenue to get there, that growth may not be sustainable. Conversely, a company sitting on a comfortable 20% profit margin but growing only 5% a year is arguably underperforming in a market where competitors are compounding faster.
By adding the two together, the Rule of 40 flags both failure modes: hypergrowth funded by unsustainable burn, and profitable-but-stagnant businesses that are quietly losing ground. A company can fail the Rule of 40 by being unprofitable and slow-growing, but it can pass by being strong in either dimension, or reasonably good at both.
How growth-stage and profitability-stage companies trade off
In practice, companies tend to sit at different points along the Rule of 40 curve depending on their stage:
- Early-stage, high-growth companies often run at low or negative margins, funding growth with venture capital. A company growing 55% with a -15% margin still scores 40. The growth carries the score.
- Mature, profitability-focused companies often see growth slow as the market matures, so they lean on margin to compensate. A company growing 15% with a 25% margin also scores 40. The margin carries the score.
- Best-in-class companies manage to post strong numbers on both axes at once, comfortably clearing 40% with room to spare.
Neither end of the curve is inherently "better." The Rule of 40 is agnostic about how a company gets to 40, only that it gets there. That said, investors and boards typically look at where on the curve a company sits, and whether it's moving toward the balanced middle over time, not just whether it clears the bar in a single quarter.
The Rule of 40 isn't a substitute for cash runway
Because the Rule of 40 collapses two numbers into one, it's easy to treat a passing score as a clean bill of health. It isn't. A company can pass the Rule of 40 while still being months away from running out of cash, if its growth is expensive to sustain and its runway is short. The Rule of 40 says nothing about how much cash is in the bank, how much of it is being spent per dollar of new ARR, or how long the current trajectory can continue before the next fundraise is needed. It's best read as one input into a broader financial picture, alongside cash runway, burn multiple, and the balance sheet, rather than a standalone verdict.
Common pitfalls
The margin definition you choose changes the score. As shown above, EBITDA margin and free cash flow margin can diverge meaningfully for the same underlying business, since EBITDA excludes non-cash and financing items that free cash flow captures. Comparing a Rule of 40 score calculated on EBITDA margin against a peer's score calculated on FCF margin isn't a fair comparison, even if both companies call it "the Rule of 40." Always check (or state) which margin is behind the number.
The metric says nothing about ARR size. The Rule of 40 is a ratio, so it's blind to scale. A $2M ARR company scoring 45% is likely riding a wave of early hypergrowth with a thin or negative margin, while a $200M ARR company scoring 45% might be growing more moderately on the back of real operating leverage. Both "pass," but the risk profile, the fundraising position, and the sensitivity to a growth slowdown are entirely different. Use the Rule of 40 alongside absolute ARR and margin figures, not as a replacement for them.
A single quarter or month is noisy. Growth rate and margin can both swing meaningfully over a short window (a large annual contract renewal, a one-off cost, a seasonal dip). Most practitioners look at the Rule of 40 on a trailing-twelve-month basis rather than a single period, to smooth out short-term noise.