The Rule of 40 for Software Companies

The Rule of 40 says a healthy software company’s revenue growth rate plus its profit margin should add up to at least 40 percent. It is a quick sanity check that balances growth against profitability, recognising that a company can justify thin margins if it is growing fast, or slower growth if it is highly profitable. It is a useful filter, but it is a starting point for analysis, not a substitute for it.

Where this fits: the Rule of 40 is a quality screen that feeds the first and fifth of our Five Criteria, and it is best understood alongside different business models explained for investors, because it only makes sense for a particular kind of business.

The Trade-Off the Rule Captures

Software companies, especially subscription or SaaS businesses, face a constant tension between growing fast and making money.

A young software company can spend heavily on sales, marketing and product to win customers quickly. That spending depresses margins today but builds a larger, recurring revenue base for tomorrow. Alternatively, a more mature software company can dial back that spending, grow more slowly, and throw off healthy profits.

Neither is automatically right. The Rule of 40 exists to judge both on a common scale. It says: it does not matter whether your strength is growth or profitability, as long as the two together clear a sensible bar. A company growing 40 percent while breaking even passes. So does one growing 10 percent with a 30 percent margin. What fails is a company that is neither growing fast nor making money, the worst of both worlds.

How to Calculate It

The formula is as simple as it sounds.

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

Both inputs are percentages, and a score of 40 or more is considered healthy. The judgement lies in choosing the right margin.

Margin used	What it reflects	Verdict
Free-cash-flow margin	Actual cash generated after all real costs	Most honest
Operating margin	Profit from operations before financing	Reasonable
EBITDA margin	Earnings before several real costs	Flattering; use with care

Our strong preference is the free-cash-flow margin, because it reflects the cash the business actually keeps after funding its own growth. A score built on EBITDA, which ignores depreciation and often share-based pay, can look impressive while the company burns cash. Whichever you choose, apply it consistently when comparing companies.

A Worked Example (Hypothetical)

Imagine three companies, all clearly hypothetical software businesses, each assessed on free-cash-flow margin.

Company	Revenue growth	FCF margin	Rule of 40 score
GrowthCo	45%	−8%	37
BalanceCo	25%	20%	45
MatureCo	8%	35%	43

GrowthCo is growing fast but burning cash, and its score of 37 falls just short. BalanceCo blends solid growth with real profitability for a score of 45. MatureCo grows slowly but is highly profitable, also clearing the bar at 43.

The insight is that BalanceCo and MatureCo look very different on the surface, one a grower, one a cash machine, yet both pass. GrowthCo’s rapid growth does not quite compensate for its cash burn, which is exactly the kind of judgement the rule is designed to force. It stops you from being dazzled by a headline growth rate that is being bought with losses.

Where the Rule of 40 Is Useful

Used in the right place, the rule is a genuinely helpful filter.

• Comparing SaaS businesses at different stages, from high-growth to mature, on a single scale.
• Screening a long list of software names down to those worth a closer look.
• Tracking a single company over time, to see whether it is trading growth for profitability sensibly or sliding on both fronts.
• Sanity-checking a growth story, by asking whether rapid growth is being funded by unsustainable losses.

That last use matters most. A company growing 50 percent sounds wonderful until you notice it is losing money at a rate that will require constant dilution or debt to sustain. The rule reframes the question from “how fast is it growing?” to “how fast is it growing, and at what cost?”

Where It Breaks Down

The Rule of 40 is a heuristic, and like all heuristics it has sharp limits. Lean on it too hard and it will mislead you.

• It only fits software. The rule was built for high-margin, recurring-revenue businesses. Applied to a bank, a retailer or a manufacturer, where margins and capital intensity work completely differently, it produces nonsense.
• It ignores the moat. A passing score says nothing about whether a company has a durable competitive advantage. A business can clear 40 today and be overtaken by a better-funded rival tomorrow. Judging that requires the thinking in how to spot a competitive advantage.
• It ignores management and capital allocation. The rule cannot tell you whether leadership is honest or whether it reinvests cash wisely.
• It is silent on price. This is the big one. A company can score 50 on the Rule of 40 and still be a terrible investment if you pay too much for it. The rule is about business quality, not valuation.
• It can be gamed. A generous margin definition that strips out share-based compensation flatters the score while real dilution eats into your returns. Always check what is being counted.

That final point on price deserves emphasis. The single largest risk to your returns is overpaying for a good business. A high Rule of 40 score often attracts a rich valuation, and a rich valuation is precisely where the danger lies. The rule identifies quality; it does nothing to protect you from paying too much for it.

Fitting the Rule Into the Five Criteria

So where does a screening tool like this belong? It informs the Five Criteria without replacing any of them.

• Criterion 1, a great business. A consistent Rule of 40 score is supporting evidence of quality, though you still want to see high returns on invested capital.
• Criterion 2, a durable moat. The rule is silent here. You must assess the moat separately.
• Criterion 3, aligned management. Also silent. Read the proxy and the capital-allocation record.
• Criterion 4, a sound balance sheet. A company burning cash to hit its growth number may be relying on a weak balance sheet, so check it.
• Criterion 5, a reasonable price. The rule says nothing about price. A high score is a reason to investigate, never a reason to buy at any multiple.

Treat the Rule of 40 as a fast first filter for software names, then do the real work. It tells you which companies deserve your attention. It does not tell you which to buy, and it certainly does not tell you what to pay. For that, you still need a proper valuation and a margin of safety.

Frequently Asked Questions

How do you calculate the Rule of 40? Add the company’s year-on-year revenue growth rate to its profit margin, both as percentages. If a software firm grows revenue 30 percent and has a 15 percent free-cash-flow margin, its Rule of 40 score is 45, which clears the threshold. The specific margin you choose, operating or free cash flow, changes the result, so be consistent.

Why 40 and not some other number? Forty is a rule of thumb that emerged among software investors and venture capitalists as a practical benchmark for a healthy subscription business, not a mathematical law. It captures the idea that growth and profitability are substitutes to a degree. Treat it as a reference point, not a precise cut-off.

Does the Rule of 40 apply to non-software companies? It was designed for software, especially subscription or SaaS businesses with high gross margins and recurring revenue. Applying it to a manufacturer, retailer or bank gives misleading results, because their economics and margin structures are completely different. Use it only where it fits.

Can a company game the Rule of 40? Yes. A company can flatter the score by using a generous margin definition that excludes share-based compensation, or by pairing unsustainable growth with heavy losses. Always check which margin is being used and whether the growth is durable before trusting the number.

Your Next Step

Pick one software company you follow and calculate its Rule of 40 score using free-cash-flow margin, not EBITDA. Then ask the questions the rule cannot answer: does it have a moat, is management sound, and is the price reasonable?

To build out the surrounding analysis, read how to spot a competitive advantage (moat) in any business and price to free cash flow, the metric Warren Buffett loves. Then score the whole company against our Five Criteria stock scorecard.

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About the author: Cameron Hayes is a senior investor relations and finance professional who has worked in IR at Nasdaq Copenhagen-listed companies including Nilfisk and Maersk Drilling. He holds an MSc from Copenhagen Business School and a BCom from the University of Ottawa, and founded Gingernomics to teach individual investors the Five Criteria framework. More about Gingernomics.

The content on Gingernomics is for educational and informational purposes only and does not constitute financial advice. Always do your own research and consult a licensed financial advisor before making any investment decisions. Past performance is not indicative of future results.