Rule of 40 answers a question that neither growth screening nor margin screening can answer alone: is this software business trading growth for profitability in a healthy way, or just burning cash to post a bigger top-line number? It's a US-born metric, standard in SaaS and software investing circles, and it applies just as well to European tech — a segment that gets far less dedicated screening content than its US counterparts.
Last updated: July 2026.
What Rule of 40 measures
Rule of 40 = Revenue Growth Rate (%) + Profit Margin (%)
A company passes the rule if the sum is 40 or higher. The specific margin used varies by convention — some use operating margin, others use EBITDA margin, and many SaaS-specific analyses use free cash flow margin (free cash flow ÷ revenue). The exact choice matters less than being consistent when comparing companies.
Example: A software company growing revenue at 25% with a 20% operating margin scores 45 — passes comfortably. A company growing at 60% with a -30% operating margin scores 30 — fails, despite the impressive growth headline, because the cash being burned to achieve it isn't yet being offset by any profitability.
Why the rule exists
The logic: growth and profitability are substitutes for each other in the early-to-mid life of a software business, and investors should be indifferent, within limits, to how a company splits the 40 between the two. A company growing at 40% with 0% margin and a company growing at 10% with 30% margin both "pass" — the rule treats aggressive, cash-burning growth and mature, profitable stability as equally acceptable, as long as the combination clears the bar.
What the rule flags is the failure mode: low growth combined with low or negative margin. A software company growing revenue at 8% while still burning cash at a -15% margin scores -7 — it has neither the growth to justify the investment thesis nor the profitability to be a mature cash generator. This is the combination Rule of 40 is specifically designed to catch.
Applying it to European tech
European software and tech companies are underrepresented in Rule of 40 discussion, which is almost entirely US-centric in its default framing — Datadog, Snowflake, and Salesforce show up in every US Rule of 40 writeup; SAP, Temenos, and Nordic SaaS names almost never do.
Why this matters for screening:
- European SaaS multiples are generally lower than US peers for comparable growth and margin profiles — applying the same Rule of 40 lens to European names can surface companies that pass the test just as well as their more richly-valued US counterparts, at a lower entry multiple.
- European software companies often lean toward the profitability side of the rule rather than the pure-growth side, reflecting a generally more conservative capital-raising and burn culture than venture-funded US software. A European SaaS company growing at 18% with a 22% margin (scoring 40) is a very different risk profile from a US peer growing at 45% with a -15% margin (also scoring 30, technically failing) — same framework, different starting point.
- Coverage of small- and mid-cap European tech is thin among generalist screeners, meaning Rule of 40 candidates outside the largest names (SAP, Dassault Systèmes) are more likely to be under-followed and mispriced relative to their US counterparts.
Building a Rule of 40 screen
Since Rule of 40 is a derived combination rather than a single stored field, build it from revenue growth and a chosen margin metric together:
Basic Rule of 40 screen (operating margin variant):
- Sector: Technology / Software
- Revenue growth (YoY) + Operating margin ≥ 40
- Sort by: combined score descending
Conservative variant (favouring the profitable side of the rule):
- Revenue growth (YoY) > 10%
- Operating margin > 15%
- (Sum comfortably clears 40, weighted toward sustainable profitability rather than pure growth)
Aggressive-growth variant (favouring growth, tolerating thin or negative margin):
- Revenue growth (YoY) > 35%
- Operating margin > -10% (burn is bounded, not unlimited)
- (Sum clears 40 primarily through growth)
The failure-mode screen (explicitly surfacing the combination to avoid):
- Revenue growth (YoY) < 15%
- Operating margin < 0%
- This combination — sub-scale growth without profitability — is the pattern Rule of 40 is built to flag as a warning, not an opportunity
What Rule of 40 doesn't tell you
It says nothing about valuation. A company scoring 55 on Rule of 40 can still be priced for perfection at 20x sales. Pair the screen with an EV/Sales check before treating a high score as a buy signal on its own.
It treats all margin sources as equivalent, which they aren't. Operating margin, EBITDA margin, and free cash flow margin can diverge significantly for a software company with heavy stock-based compensation or capitalised development costs. Be consistent about which margin you use, and be aware that a company can look meaningfully better on an EBITDA-margin version of the rule than on a free-cash-flow-margin version.
It's most meaningful for subscription/recurring-revenue businesses. The 40 threshold and its general interpretation were built around SaaS economics — predictable, recurring revenue with high incremental margins. Applying it to a hardware company, a services business, or a cyclical tech name distorts the comparison; the rule works best on companies where the underlying revenue model resembles the one it was designed for.
A single-period score can mask a deteriorating trend. A company scoring 42 this year after scoring 55 last year is decelerating on both dimensions even though it technically still "passes." Track the trend, not just the current snapshot.
Common mistakes when screening by Rule of 40
Applying it outside software/tech: The rule was built around recurring-revenue software economics. Applying the same 40 threshold to industrials, retail, or cyclical names produces a meaningless comparison.
Ignoring which margin definition is being used: A company's Rule of 40 score can look very different depending on whether operating margin, EBITDA margin, or FCF margin is used. Always check — and be consistent — when comparing companies against each other.
Treating 40 as a hard pass/fail line: A score of 38 isn't meaningfully different from 42. Use it as a continuous ranking signal within a peer group rather than a strict binary cutoff.
Ignoring the split between growth and margin: Two companies can score identically on Rule of 40 with very different risk profiles — one built entirely on growth with no profitability, one built entirely on margin with minimal growth. The composition matters as much as the total.
Bottom line
Rule of 40 is a fast, single-number way to combine growth and profitability for software and recurring-revenue businesses — and one that's applied far less often to European tech than to its US counterparts, despite working identically well. Screening European names against the same 40 threshold, with awareness of which margin definition is in use, surfaces candidates in a segment that gets meaningfully less dedicated attention than the US SaaS universe that dominates the metric's usual coverage.
Frequently asked questions
What is the Rule of 40 in investing?
Rule of 40 is a heuristic for evaluating software and recurring-revenue businesses: revenue growth rate (%) plus profit margin (%) should sum to at least 40. It treats growth and profitability as substitutes — a company can pass by growing fast with low margin, growing slowly with high margin, or any combination that clears the threshold.
Which margin should I use for Rule of 40 — operating, EBITDA, or free cash flow?
All three are used in practice, and the choice matters. Operating margin and EBITDA margin are more consistently available across companies; free cash flow margin is often preferred for SaaS specifically because it captures the actual cash economics, including capitalised development costs and working capital effects. Be consistent about which one you use when comparing companies.
Does Rule of 40 work for European tech stocks?
Yes — the underlying logic (growth and profitability as substitutes for recurring-revenue businesses) applies identically to European software companies. It's simply applied far less often to European names in available research and screening content, which is heavily oriented toward US SaaS companies.
Is a Rule of 40 score above 40 a buy signal?
Not on its own. It indicates the combination of growth and profitability meets a commonly used bar for software business health, but it says nothing about valuation. A company can score well above 40 and still be priced too richly relative to that growth and profitability profile — pair the screen with a valuation check before treating it as an actionable signal.
Screen European tech stocks by revenue growth and margin → — free, no account required. Build a Rule of 40 screen across European technology and software companies.