What Is Rule of 40 and Why Should Growth Investors Care?

A simple metric that captures the most important trade-off in growth investing: the balance between how fast a company is growing and how profitably it is doing it.

Educational content only. This post does not constitute financial advice.

The Rule in One Sentence

Rule of 40 says that a healthy growth company's revenue growth rate plus its profit margin should equal or exceed 40%.

That is it. One number. One threshold. And it tells you something remarkably useful about whether a growth company's economics actually work.

The Formula

Examples:

• 35% growth + 10% margin = 45 ✓ Passes
• 50% growth + (-20%) margin = 30 ✗ Fails
• 15% growth + 30% margin = 45 ✓ Passes

Why It Works

Growth investing is built on a trade-off. Fast-growing companies typically sacrifice profitability to fuel expansion — they spend heavily on R&D, sales, and marketing to capture market share. This is rational behaviour if the market is large enough and the business model has high gross margins. But it creates a problem: how do you know if the trade-off is working?

Revenue growth alone does not answer this. A company can grow at 60% per year while destroying value if the economics are broken — if it costs more to acquire each customer than the customer will ever return. Many companies in the 2020-2021 bubble did exactly this.

Profitability alone does not answer it either. A company with 30% EBITDA margins but zero growth is not a growth investment — it is a mature business.

Rule of 40 combines both dimensions into a single check. It allows for different mixes: high growth with low margins, moderate growth with high margins, or anything in between. What it demands is that the combination exceeds a minimum threshold of quality.

This flexibility is what makes it useful. It does not penalise a company for being unprofitable if it is growing fast enough to justify the investment. And it does not penalise a company for growing slowly if it is highly profitable. It only penalises companies where neither growth nor profitability is sufficient.

Where It Came From

Rule of 40 originated in venture capital and private equity, where it was used as a quick health check for SaaS (Software as a Service) businesses. The logic: SaaS businesses with high gross margins should be able to achieve some combination of 40%+ growth-plus-margin because the underlying business model supports it.

Over time, the metric has been adopted more broadly across growth investing. It is not perfect — no single metric is — but it captures a fundamental truth about growth economics that more complex metrics often obscure.

What GrowthPicks Does With It

In the GrowthPicks model, Rule of 40 acts as a constraint on enthusiasm, not a score component. This is an important distinction.

The model does not reward companies for having a high Rule of 40. Instead, it uses Rule of 40 to restrain conviction when the growth-plus-profitability balance is poor. A company with excellent revenue growth but a deeply negative margin — one that fails Rule of 40 — will see its score moderated. The model is saying: "the growth is impressive, but the economics are not yet sound enough to justify full conviction."

This aligns with the GrowthPicks philosophy: Rule of 40 constrains enthusiasm — it does not replace judgement.

Every ticker in the GrowthPicks universe has its Rule of 40 displayed on the Detail page, in the Valuation card. You can also see it as a data point when evaluating any company on the Compare page.

Rule of 40 Scale

Common Misconceptions

"Rule of 40 only applies to SaaS." The metric was popularised in SaaS, but the underlying principle applies to any growth business. A high-growth hardware company or a fast-scaling fintech faces the same trade-off between growth and profitability. The 40% threshold may be harder to achieve for lower-margin business models, but the concept is universally relevant.

"Above 40 is good, below 40 is bad." Rule of 40 is a spectrum, not a pass/fail. A score of 38 is not meaningfully worse than 42. The metric is most useful at the extremes: a score above 60 signals an exceptional combination of growth and profitability, while a score below 20 signals a business that is neither growing fast nor making money.

"Rule of 40 captures everything about quality." It does not. Rule of 40 says nothing about gross margins, free cash flow, dilution, debt, or customer concentration. It is one lens among several. In the GrowthPicks model, it works alongside the Growth Score, Quality Score, Value Modifier, and Risk Flags to build a complete picture.

Example Companies

A Quick Example

Consider two companies in the GrowthPicks universe:

Company A: 45% revenue growth, -10% EBITDA margin. Rule of 40 = 35. Fails the threshold. Growing fast, but burning cash at a concerning rate. The model will moderate its conviction.

Company B: 22% revenue growth, 25% EBITDA margin. Rule of 40 = 47. Passes comfortably. Not the fastest grower, but profitable and sustainable. The model will not penalise it.

Both are legitimate growth investments. But the Rule of 40 metric surfaces a crucial difference in their risk profiles. Company A needs to improve its economics before the growth truly compounds for shareholders. Company B is already compounding.

The Takeaway

Rule of 40 is not a magic number. It is a lens. It forces you to consider growth and profitability together — rather than being seduced by one and ignoring the other.

If you take one thing from this post: the next time you look at a growth company's revenue growth rate, ask yourself what the EBITDA margin is. Add them together. If the answer is below 40, ask why — and whether the path to improvement is credible.

The full guide — Understanding Rule of 40 [G-06] — goes deeper into the calculation, edge cases, and how the GrowthPicks model uses it. It is available in the Toolkit.

GrowthPicks is an educational and analytical tool. Nothing in this post constitutes financial advice or a recommendation to buy, sell, or hold any security. Always do your own research.