Rule of 40 — why 40% is the magic number for SaaS
Rule of 40 — why 40% is the magic number for SaaS
In 2015 Brad Feld (Foundry Group) published a short post that defined how to judge the health of public SaaS companies for the next decade. The formula is simple:
> YoY revenue growth (%) + margin (%) ≥ 40%
If the sum is ≥ 40, the company is "healthy". Above 60 is top decile. Below 40 means you need to either grow faster or become more profitable.
Why exactly 40%?
Brad Feld didn't derive the number mathematically — it's an empirical observation from analyzing public SaaS. He noticed that companies with R40 ≥ 40 trade at a premium on multiples versus companies with R40 < 40.
After 2015 dozens of funds (OpenView, Bessemer, ICONIQ) verified the pattern across different datasets. It holds consistently:
- Too much growth with no margin = losses, unsustainable
- Too much margin with no growth = stagnation, losing to competitors
- 40% is the sweet spot between those two extremes
Which margin should you use?
3 options:
| Margin type | When to use | ||
|---|---|---|---|
| EBITDA margin | Most commonly used, for private SaaS | ||
| Operating margin | Close to EBITDA, but includes depreciation | ||
| FCF margin | Public SaaS report this, the most conservative |
2026 benchmarks
After the ZIRP correction, the Rule of 40 got harder to hit. Public SaaS medians:
| Tier | R40 | Examples (public SaaS) | ||
|---|---|---|---|---|
| Top decile | >60% | Adobe, ServiceNow, CrowdStrike, Cloudflare | ||
| Top quartile | 40-60% | Datadog, Snowflake (post-IPO) | ||
| Median public SaaS | 25-35% | Most mid-tier names | ||
| Bottom quartile | <20% | Cut costs now or pivot to profit |
- 40-55% — the best mix
- Well above 60% — usually under-investing in growth (could grow faster if they invested)
A worked example
A SaaS startup:
- ARR at start of year: $5M
- ARR at end of year: $7M → growth = 40% YoY
- EBITDA: -$500k (-7% margin)
R40 = 40 + (-7) = 33 → below the healthy threshold
To reach R40 = 40:
- Option A: accelerate growth from 40% → 47% YoY
- Option B: improve margin from -7% → 0% (reach break-even)
- Option C: a mix — 43% growth + -3% margin = 40 ✓
Use the calculator below to model your own scenario.
When the Rule of 40 does NOT apply
It's a metric for public-ready SaaS at scale. Don't apply it to:
1. Pre-product-market-fit — growth is unstable by definition, margin is wild
2. Hardware-heavy businesses — capex distorts margin
3. Marketplace models — take-rate matters more than growth+margin
4. Deep tech, biotech — long R&D cycles make early-stage margin nonsense
Why is top decile = >60%?
Public SaaS companies in the top deciles usually reach R40 >60% not by sacrificing growth but through operating leverage:
- Margin improves with scale — more revenue → better gross margin (S&M scales sublinearly)
- Brand awareness lowers CAC → S&M as a % of revenue falls
- Self-serve onboarding removes CSM cost in the SMB segment
- R&D is reused across new products (Datadog: 1 platform → 20+ modules)
In other words, R40 >60% = proof of product-market fit + operational excellence + recurring expansion economics.
3 levers to improve R40
1. Pricing review
A 10% price increase typically adds +5-8% to gross margin without losing customers (if the value prop exists). It's the cheapest way to improve R40 by 5-8 points.2. Gross margin
Audit COGS:- Hosting (AWS optimization, reserved instances)
- Customer support (deflect via docs, AI)
- Payment processing (negotiate with Stripe at scale)
Every +5% of gross margin = +5 points of R40.
3. Expansion revenue
Existing-customer revenue has a CAC of ~$0:- Seat-based / usage-based pricing
- Tiered features → natural upgrade path
- Account-based marketing for high-ARR accounts
NRR >115% automatically adds ~10-15% of growth "for free" (without new customers).
Real-world R40 examples
| Company | Year | Growth | Margin | R40 | ||
|---|---|---|---|---|---|---|
| Snowflake | 2024 | 35% | 8% (FCF) | 43 | ||
| Datadog | 2024 | 27% | 30% | 57 | ||
| HubSpot | 2024 | 23% | 15% | 38 | ||
| Salesforce | 2024 | 11% | 32% | 43 | ||
| Shopify | 2024 | 26% | 19% | 45 |
Bottom line
The Rule of 40 is a simple metric for the board room and investor pitch. It's not the only one, not a magic number, but it's universally understood. Know yours, track it quarterly, and explain the trajectory (is it improving every Q?).
Calculate your R40 below — see the interactive calculator across different growth + margin scenarios.
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Further resources
- Brad Feld's original 2015 post
- Bessemer State of the Cloud 2024
- /en/burnMultiple — Burn Multiple, a complementary metric
- /en/grossMargin — Gross Margin, one of the R40 inputs
- /en/mrrGrowthRate — the growth half of the formula