What Is the Rule of 40 in SaaS?
The Rule of 40 states that a SaaS company's revenue growth rate plus its profit margin should equal or exceed 40. A company growing 60% with a negative 20% margin scores 40. So does one growing 15% at a 25% margin. The metric was popularised by Brad Feld of Foundry Group and is now the first number most investors calculate about a software business.
It exists because SaaS forces a trade-off. You can buy growth by burning cash, or protect margin and grow slowly. The Rule of 40 puts both sides on one line so neither can be hidden behind the other.
How do you calculate the Rule of 40?
Add your revenue growth rate to your profit margin. Both as percentages, both over the same period.
Revenue growth rate + profit margin ≥ 40
Two inputs, and both of them are arguments.
Growth rate. Use year-on-year recurring revenue growth. ARR is the cleanest input for a subscription business because it strips out one-off services revenue that flatters the number.
Profit margin. This is where scores diverge. EBITDA margin is the most common choice. Free cash flow margin is stricter and increasingly what investors ask for. GAAP operating margin is the harshest. The same company can score 45 on one basis and 28 on another, which is why you should know all three before a fundraise rather than during one.
A worked example. A company at £6m ARR growing to £8.4m has a 40% growth rate. If it runs at a negative 10% EBITDA margin, the score is 30. Below the line, and the gap tells you the size of the problem: either 10 points of growth or 10 points of margin.
What counts as a good Rule of 40 score?
Forty, and it is harder to hit than the round number suggests.
McKinsey's analysis of more than 200 software companies between 2011 and 2021 found that businesses exceeded Rule of 40 performance only 16% of the time, and roughly a third achieve it in any given year (McKinsey, 2021). Sustaining it across several years is rarer still.
The payoff for the ones that do is a valuation premium rather than a pat on the back. The same research found top-quartile SaaS companies generate close to three times the EV to revenue multiples of bottom-quartile companies.
Stage changes what a good score looks like in practice. Early companies clear the bar on growth alone, often at a heavy margin deficit. As growth decelerates past roughly £40m ARR, the margin side has to carry more of the weight, and the companies that fail are usually the ones that did not start building margin before growth slowed.
Why do investors care about the Rule of 40?
Because it is the fastest way to tell whether growth is being bought or earned.
A 70% growth rate looks excellent until you see it costs a negative 50% margin to produce. The Rule of 40 collapses that into one number an investor can compare across a portfolio without opening the model. It is a screening tool, and it is used as one: below 30 with decelerating growth, a company needs a credible improvement story in the investment thesis before anyone goes further.
It also works as an early warning internally. When the score drops for two consecutive quarters, the cause is more often a headcount-driven margin issue than a revenue problem, and it shows up in the score before it shows up anywhere a board would notice.
Where the Rule of 40 breaks down
It is a heuristic, not a law, and treating it as a target has three known failure modes.
It is meaningless below scale. A company at £1m ARR growing 200% scores 150 on a rounding error. The metric was built for businesses at scale and says almost nothing about a seed-stage company.
It rewards cutting the wrong costs. Margin can be improved in a quarter by stopping marketing spend. The score goes up. The pipeline that would have produced next year's growth does not exist, and the score goes down harder twelve months later. Any metric that can be gamed inside one quarter will be.
It hides which side is broken. Two companies both scoring 40 can be in completely different health. One is growing 60% and investing hard. The other is growing 5% at a 35% margin and has stopped competing. The number is identical and the futures are not.
Read it alongside a sales efficiency metric rather than on its own. A healthy SaaS magic number above 0.75 tells you the growth half of your Rule of 40 score is being produced efficiently rather than bought.
What the Rule of 40 means for your marketing budget
This is the part that gets skipped, and it is the part that affects what marketing gets funded.
When a board starts managing to the Rule of 40, marketing spend becomes the most visible lever on the margin side. It is discretionary, it is large, and cutting it improves the score immediately. That is why efficiency arguments beat volume arguments in a Rule of 40 conversation, and why channels that compound are worth more than channels that stop the day you stop paying.
Three practical consequences:
- Paid media is structurally exposed. Spend stops, cost stops, margin improves. If your pipeline depends on it, your growth number falls at the same time, which is the trade the Rule of 40 is designed to expose.
- Organic gets more valuable as growth slows. Content and search keep producing after the spend stops, so they improve the margin side without immediately damaging the growth side. This is the core commercial argument for inbound marketing in SaaS.
- Attribution stops being a reporting nicety. If you cannot show which spend produced which pipeline, marketing is the first budget cut when the score dips, because nobody can price the consequence.
Team 4 builds every organic programme against pipeline rather than traffic for exactly this reason. The full picture of how the channels fit together sits in our guide to B2B SaaS marketing.
Frequently asked questions
Who invented the Rule of 40?
The Rule of 40 was popularised by venture capitalist Brad Feld of Foundry Group, who wrote about it in 2015, though the underlying idea circulated among software investors before that. It was later validated at scale by McKinsey's research into software company shareholder returns.
Should I use EBITDA or free cash flow for the Rule of 40?
Both, and know the gap between them. EBITDA margin is the most common convention and produces the friendlier number. Free cash flow margin is stricter and is what an increasing number of investors ask for first. Calculate on both bases before a fundraise so you are not surprised by someone else's version of your score.
Does the Rule of 40 apply to early-stage SaaS?
Not usefully. Below roughly £5m to £10m ARR the growth rate dominates the calculation to the point where the score stops being informative. Early-stage companies are better judged on net revenue retention, magic number and CAC payback, which say something about the underlying engine.
What is a bad Rule of 40 score?
Below 30 with decelerating growth and a negative margin is the combination investors treat as a problem, because neither half of the equation is trending the right way. A score below 40 driven purely by heavy growth investment is a different conversation and is often acceptable at the right stage.
About Team 4
Team 4 is a B2B SaaS marketing agency in London. We build Inbound Engines for seed to Series B software companies: SEO, GEO, content, paid media and CRO run as one system and measured against pipeline rather than traffic. When boards start managing to efficiency metrics, marketing that cannot prove its contribution is the first thing cut, so we set up attribution before we set up campaigns.
