Rule of 40

What the Rule of 40 Measures

Brad Feld coined it in a 2015 blog post, watching late-stage SaaS companies trade growth for profitability and pretending the math was hidden. The Rule of 40 makes the math visible. A company growing 60% year-over-year at -20% margin clears it. So does one growing 10% at 30% margin. Anything below 40 means you're burning cash without buying enough growth to justify it.

The rule is operator shorthand for "are you building a business or lighting capital on fire."

How the Rule of 40 Is Calculated

The formula:

Revenue Growth Rate (%) + Profit Margin (%) ≥ 40

Inputs vary by audience. Public-markets analysts default to free cash flow margin. Late-stage private boards default to EBITDA. Early-stage boards usually skip the rule entirely because the denominator's too small to mean anything yet. Growth is measured as year-over-year ARR growth, or sometimes GAAP revenue growth — and the choice changes the answer by hundreds of basis points.

Worked Rule of 40 Example

Companies A and B both clear 40 with very different mixes. A is the land-grab. B is the mature operator. Both are healthy under this lens. C looks hot but isn't paying its way. D is comfortable but coasting — the kind of company a strategic acquirer underbids because growth has stalled and margin can't expand further without cutting the muscle.

When SaaS Boards Use the Rule of 40

The rule appears in three rooms:

• Board decks, where the CFO uses it to defend or attack the spending plan
• IPO bake-offs, where bankers benchmark candidates against public comps like Snowflake, Datadog, and ServiceNow
• Acquisition diligence, where strategic buyers use it to price revenue multiples

For revenue leaders, the rule decides whether next year's hiring plan survives the budget cycle. A company below 40 will cut SDR headcount and lengthen ramp expectations before it cuts engineering. A company well above 40 will overinvest in pipeline generation and accept thinner forecast accuracy in exchange for top-line aggression. ICs rarely see the metric explicitly. They feel it as quota inflation in years the score runs hot, and quota relief in years it collapses.

Common Rule of 40 Gaming Patterns

The number is easy to flatter. Three moves to watch for:

Margin definition shopping. Companies swap between adjusted EBITDA, non-GAAP operating margin, and FCF depending on which one clears the bar. Adjusted EBITDA at most SaaS companies excludes stock-based compensation, which is a real cost paid in real dilution. A company reporting "55 on the Rule of 40" while diluting shareholders 8% a year is reporting a number that doesn't survive a serious analyst's spreadsheet.

Growth-rate cherry-picking. Reporting growth on a constant-currency basis. Reporting "subscription revenue" while excluding services drag. Reporting a trailing-three-quarters annualized run rate instead of full-year YoY. Each is defensible. Each gives you 200 to 500 basis points of free growth.

ARR inclusions. Counting annual contract value from multi-year deals signed but not yet started. Treating one-time professional services as recurring. Pulling expansion ARR forward by re-papering existing accounts in Q4 to reset the contract date.

The rule itself is blunt. It doesn't distinguish growth that's durable from growth bought with unsustainable customer acquisition cost. Two companies at 45 can have radically different net revenue retention — and the one with NRR at 90 is going to struggle next year while the one at 130 compounds. Use the rule as a first filter, not a verdict.