How is the Rule of 40 calculated?

Add a revenue growth rate to a profit margin measured over the same period; a sum at or above forty passes the screen. The catch is that both inputs have competing definitions — total revenue growth versus recurring-revenue growth, free-cash-flow margin versus operating margin — and different choices commonly produce different scores for the same company. A quoted score means little without its inputs named.

Which profit margin should be used in the Rule of 40?

Practice varies: free-cash-flow margin, operating margin, and adjusted profitability figures all appear in the wild. No single choice is canonical. What matters more than the pick is consistency — choosing one definition, stating it, and holding it constant so the score's movement over time carries meaning.

Does the Rule of 40 apply to early-stage companies?

Generally poorly. Growth from a small revenue base tends to be jumpy and flattering at once, and early margins move with individual hires and contracts rather than with underlying economics. Below meaningful scale the screen mostly reports arithmetic on small denominators. Capital-efficiency measures such as burn multiple usually tell a young company more.

Is a score above forty proof of a healthy business?

No. The rule is a screen, not a verdict — a way to sort many companies quickly into worth-a-closer-look and probably-not. A passing score can hide weak retention, deteriorating unit economics, or accounting choices that flatter one input, which is why the score works best as a doorway to questions rather than an answer.

What is the Rule of 40

Guide · Glossary & Definitions · 4 min read · last verified 2026-07-28

Reviewed before publication Editorial board Independent commercial review

In shortThe Rule of 40 adds growth rate to profit margin and screens for a sum of forty or more. What the heuristic encodes, why it is shorthand rather than law, and where it misleads — below scale and across business models.

The Rule of 40 is a screening heuristic for software companies: add the revenue growth rate to the profit margin, and a combined score at or above forty counts as passing the screen. A business growing fast while losing money and a business growing slowly while comfortably profitable can land on the same score — that exchangeability is what the heuristic was built to express, and also the source of most of its misuse.

The arithmetic

Take a growth rate and a margin, both measured over the same period, and check whether their sum reaches forty. Nothing else enters the calculation. What makes the arithmetic slippery is not the addition but the definitions feeding it. Growth might mean total revenue growth or growth in annual recurring revenue, which diverge whenever a company has meaningful services or one-time income. Margin might mean free-cash-flow margin, operating margin, or an adjusted profitability figure, and these commonly differ from one another by a lot for the same company in the same period. Different input choices produce genuinely different scores, so anyone quoting a Rule of 40 result without naming the inputs has given you a number, not a fact. The first discipline of using the rule is simply stating which definitions you chose and holding them constant.

The trade the heuristic encodes

The rule exists to price a trade-off. Growth and profitability pull against each other in most software businesses, because growth is typically bought with spending that lands ahead of the revenue it produces. Rather than demanding both at once, the screen accepts either: a company may run deeply unprofitable if it is expanding quickly, or expand modestly if it is solidly profitable, so long as the sum clears the bar. That gives investors and operators a single axis on which very different companies can be compared at speed — which is precisely the job of a screening shortcut, and the limit of it.

Shorthand, not physics

The Rule of 40 spread largely as investor shorthand — a fast way to sort a long list of software companies into worth-a-closer-look and probably-not — and shorthand is what it remains. The forty is a convention, not a discovered constant; nothing in software economics makes thirty-nine a failure and forty-one a success. Treating the threshold as a law invites two characteristic errors. The first is managing the company toward the score, which rewards whatever accounting choices flatter the sum. The second is inventing modified variants with friendlier thresholds when the standard one delivers bad news — an exercise that converts a screen into a self-affirmation. Its defensible uses are narrower: a prompt for the question of whether spending is converting into either growth or profit, and a shared vocabulary for the growth-versus-margin conversation a leadership team needs to have anyway.

Below scale, the inputs stop meaning much

Early-stage companies tend to break both halves of the sum. Growth measured from a small base can look spectacular while saying little — early revenue often arrives in lumps, and a single contract can swing the rate wildly from one period to the next. Margin at that stage moves with individual hires and one-off costs rather than with the underlying economics. The screen presumes enough operating history for both inputs to be stable, and below that scale it typically reports more about small denominators than about the business. For young companies, capital-efficiency measures such as burn multiple usually carry more information per glance, because they ask how much cash produced how much new recurring revenue rather than blending two noisy rates.

Across business models, scores stop comparing

Even at scale, the score travels badly between business models. A company with substantial services revenue carries a different margin structure than a pure software business; usage-based pricing shifts how growth shows up; a hardware component changes the meaning of gross margin entirely. Comparing raw scores across such models often misleads, because the sum silently assumes the growth-margin trade works the same way everywhere. The rule was popularized around subscription software economics, and the further a business sits from that shape, the less its score means next to another company's. Within one company over time, held to constant definitions, the trend of the score is far more informative than any cross-company league table built from it.

Using the score without serving it

A short list of practices keeps the heuristic in its lane. Name the inputs every time the score is quoted. Hold the definitions constant across periods so movement means something. Read the trend rather than worshipping the level. Never set the score itself as a target — the moment it becomes a goal, the incentive is to move the number by the cheapest available means rather than to improve the business underneath. And resist the urge to adjust the threshold when the verdict stings; the rule is a doorway to harder questions about where money goes and what it returns, not a verdict in itself. Used that way, it is one quick check among several — alongside efficiency and retention measures — rather than a substitute for understanding the company.