The Rule of 40, Explained — Plus the Weighted Variant

The Rule of 40 says a healthy SaaS company's revenue growth rate plus its profit margin should total at least 40%. Grow 60% while burning 20% of revenue and you score 40 — pass. Grow 10% at a 15% margin and you score 25 — you have a problem. It is the fastest single-number read on whether a software business is trading growth for profit at an acceptable exchange rate, and it is the first thing most investors compute when they open your metrics deck.

That is the whole rule. The interesting parts are the ones people get wrong: which profit metric goes into it, why the naive version undervalues growth, and what a passing score actually looks like at different growth/margin mixes. This guide covers all three, with numbers you can check against the Rule of 40 calculator.

Where the Rule of 40 came from

The rule went public in early 2015, when Brad Feld wrote up a heuristic he'd heard from a late-stage investor at a board meeting: for a SaaS company at scale, growth rate plus profitability should exceed 40%. Fred Wilson published a similar take days later, and Bessemer, Battery Ventures, and McKinsey each ran the regression against public software companies and found the same pattern — companies clearing 40 traded at premium multiples, and companies below it got punished.

The logic is a trade-off frontier. Growth and profitability compete for the same dollars: every point of margin you give up should buy you more than a point of growth, or you are lighting money on fire. The 40 line is where public markets have historically said the trade stops being worth it. It was designed for companies past roughly $10M ARR (Feld's original framing was even later-stage); below that, growth rates are too noisy and too easy — a seed startup doubling off $300K clears 40 trivially and it means nothing.

The formula — and the choices hiding inside it

Rule of 40 = Revenue growth rate % + Profit margin %

One addition, two inputs, and both inputs force a decision.

Which growth number

Year-over-year ARR growth is the standard for private SaaS; public companies use GAAP revenue growth. Two rules keep you honest. First, recurring revenue only — services and one-time fees inflate the number without the durability the rule is trying to measure. Second, match your timeframes: if growth is trailing-twelve-months, the margin must be too. Annualizing your best quarter's growth and pairing it with a full-year margin is the most common way founders accidentally (or not so accidentally) flatter the score.

Which profit metric: use free cash flow margin

You will see the rule computed with EBITDA margin, operating margin, net income margin, and free cash flow margin. Use FCF margin. Three reasons:

• It's the metric investors actually regress. Bessemer's efficiency framing and most public-market analyses pair growth with FCF margin, so using it keeps your number comparable to the benchmark everyone is quoting.
• It's harder to dress up. EBITDA can be flattered by capitalizing software development costs — the spend disappears from the P&L into the balance sheet. FCF catches it, because capitalized development is still cash out the door.
• It rewards SaaS working-capital dynamics. Annual prepay contracts pull cash forward. FCF gives you credit for collecting cash early, which is a real advantage the income statement ignores.

The honest caveat: FCF still lets stock-based compensation off the hook, since SBC is non-cash. If your SBC runs north of 10–15% of revenue, sophisticated investors will recompute your score with an SBC-adjusted margin — better to show that view yourself. And whichever metric you pick, pick it once. A company that reports EBITDA-based Rule of 40 one quarter and FCF-based the next is telling you exactly which number looked better each quarter.

The weighted Rule of 40: why growth gets a 1.33x multiplier

Weighted Rule of 40 = (1.33 × Growth %) + FCF margin %

The plain rule treats a point of growth and a point of margin as equally valuable. Markets do not. Regress public SaaS enterprise-value multiples against growth and FCF margin and the growth coefficient comes out consistently larger — depending on the period, a point of growth has been worth anywhere from 1.3x to 3x a point of margin. The reason is compounding: growth is a claim on all future years of revenue, while margin is a claim on this year's. A 30%-grower doubles in under three years; a 30%-margin business at zero growth just stays the same size, more profitably.

The weighted variant bakes in a conservative version of that premium: multiply growth by 1.33, add margin, compare against the same 40 line. The 1.33 figure sits at the cautious end of the published range on purpose — after 2022 repriced burn and made efficiency fashionable again, the growth premium compressed, and 1.33 is roughly where the post-correction regressions landed. It is a weighting the current market will actually defend, not a 2021 artifact.

What the weighting changes in practice: it rescues efficient hypergrowth and penalizes stagnant cash cows. A company growing 60% at a -25% FCF margin fails the plain rule but passes weighted comfortably. A 5%-grower at a 35% margin passes the plain rule at exactly 40 but barely scrapes by weighted. That reshuffling matches how acquirers and growth investors actually price these companies, which is the whole point of the variant.

Worked examples: three growth/margin mixes

Three companies, each at $20M ARR, trailing-twelve-month figures:

1. Hypergrowth burner. 60% ARR growth, -25% FCF margin. Plain: 60 − 25 = 35 — fails. Weighted: (1.33 × 60) − 25 = 79.8 − 25 = 54.8 — passes with room. The plain rule says this company is inefficient; the weighted rule says the burn is buying growth at a rate the market historically rewards. If the growth is durable, the weighted read is the right one.
2. Balanced operator. 25% growth, 15% FCF margin. Plain: 25 + 15 = 40 — passes exactly. Weighted: (1.33 × 25) + 15 = 33.25 + 15 = 48.25 — passes comfortably. This is the profile both versions of the rule love: growing meaningfully while self-funding.
3. Cash cow. 5% growth, 35% FCF margin. Plain: 5 + 35 = 40 — passes exactly, same score as company 2. Weighted: (1.33 × 5) + 35 = 6.65 + 35 = 41.65 — a hair over the line. The plain rule calls companies 2 and 3 identical. The weighted rule correctly ranks the balanced operator well ahead, because 25% growth compounding forward is worth far more than 30 extra margin points on a flat base.

Notice the asymmetry: the weighting never changed the pass/fail verdict for the profitable companies, but it flipped the burner from fail to pass and split a tie the plain rule couldn't see. Run your own mix through the calculator — it computes both variants side by side.

What counts as good in 2026

Unlike most SaaS metrics, the Rule of 40 target barely moves by stage — the 40 line is the 40 line whether you're bootstrapped or Series B+. What changes is how seriously to take it: below ~$10M ARR it's a directional gut-check, above that it's a number investors will hold you to. Directional 2026 medians (sources vary — synthesized from SaaS Capital, Benchmarkit/KeyBanc, and Bessemer-style public reports; treat as orientation, not gospel):

Rule of 40 score	Verdict	How investors read it
40%+	Passes	Efficient growth; premium-multiple territory
30–40%	Near the line	Fixable — one strong lever (pricing, churn, S&M efficiency) closes the gap
Below 30%	Below 40	The growth/profit trade isn't working; expect hard questions on burn

Worth knowing: the median public SaaS company spends most years below 40. Passing is genuinely top-half performance, not table stakes. Full stage-by-stage bands for this and a dozen other metrics live on the benchmarks page.

Common mistakes

• Mismatched timeframes. Quarterly-annualized growth plus trailing-year margin is not a Rule of 40 score; it's two different companies stapled together. TTM for both, or matched quarters for both.
• Metric shopping. Switching between EBITDA, operating, and FCF margin depending on which clears 40 this quarter. Diligence catches this in about four minutes.
• Counting non-recurring revenue in growth. A big services quarter or a one-time license deal spikes the score with revenue that won't repeat. Recurring revenue only.
• Ignoring SBC. An FCF margin propped up by paying people in stock isn't the margin you think it is. Show the SBC-adjusted view before someone shows it to you.
• Applying it too early. Pre-$1M ARR, growth percentages off a tiny base make the score meaningless. At that stage, quick ratio and burn and runway tell you far more about whether the machine works.
• Treating it as a snapshot instead of a trajectory. A company at 35 and climbing is a better bet than one at 42 and sliding. Track the trend quarterly, and pair it with the magic number to see whether sales efficiency is driving the move or masking it.
• Optimizing the score directly. Slashing S&M spend boosts margin now and kills growth two quarters later — the score holds, then craters. The rule measures the health of the trade-off; gaming it just delays the diagnosis.

Run your number

Take TTM ARR growth and TTM FCF margin, add them, and see where you land against 40. Then run the weighted version — if the two disagree, the gap tells you whether your profile is growth-heavy or margin-heavy, and which lever the market would rather you pull. The Rule of 40 calculator computes both variants, scores you against the 2026 bands, and takes about thirty seconds. Faster than a board meeting, and considerably cheaper.