Unit Economics
Rule of 40
Rule of 40 is a health check for software companies that says your revenue growth rate plus your profit margin should add up to at least 40%. It is a quick way to test whether you are balancing growth and profitability instead of buying growth you cannot afford.
Also known as: 40% rule, Rule of 40%, growth plus profit rule
Why it matters
For a founder past early traction, Rule of 40 is a blunt sanity check on whether your growth is real or just bought with cash you will not get back. It forces the trade-off into one number: you can grow fast and burn, or grow slow and bank margin, but the combination has to clear the bar. If you are at 80% growth and minus 50% margin, you score 30, which means the growth is propped up by spend that is not earning its keep. The number tells you what to fix: under 40 because growth stalled is a demand problem, under 40 because margin cratered is an efficiency problem, and those lead to very different decisions. Do not apply it before you have real recurring revenue and product-market fit, since a pre-PMF startup should be spending hard to find the market and the rule will just punish you for doing the right thing. Treat it as a steering metric once you are scaling, not a gate on whether to keep building.
Formula
Rule of 40 score = revenue growth rate (%) + profit margin (%). Pass if the sum is >= 40. Margin is usually EBITDA margin, free cash flow margin, or operating margin; pick one and stay consistent.
Worked example
A SaaS company does $4M ARR, up from $2.6M last year, so revenue growth is about 54%. It burns cash and runs an EBITDA margin of minus 20%. Score = 54 + (-20) = 34, which is below 40, so the growth is slightly too expensive for the pace. To clear the bar it needs to either push growth above 60% at the same burn or cut burn to roughly minus 14% margin while holding growth.
Common mistakes
- Applying it pre-product-market-fit. Before you have durable recurring revenue, low or negative margin is correct because you are funding discovery, and the rule will flag healthy spending as failure.
- Mixing margin definitions. Growth plus a flattering gross margin will sail past 40 while the company bleeds cash; use EBITDA, free cash flow, or operating margin and use the same one every quarter.
- Treating 40 as a ceiling. Good looks like 40 sustained, great looks like comfortably above 40 quarter after quarter, and a one-time spike from a deferred expense or a lumpy deal does not count.
Frequently asked questions
What is a good Rule of 40 score?
Anything at or above 40 is considered healthy, and consistently above 40 is strong. Top-tier public SaaS companies often land in the 40 to 60 range. A score in the 20s or 30s is not a death sentence, but it means your growth and profitability are out of balance and you should know exactly which lever is short.
How do you calculate Rule of 40?
Add your year-over-year revenue growth rate to your profit margin, both as percentages. If revenue grew 50% and your EBITDA margin is minus 15%, your score is 35. Use the same margin definition each period so the trend is comparable, and base it on recurring revenue rather than one-off services.
Does Rule of 40 apply to early-stage startups?
Not really. The rule assumes you already have product-market fit and durable recurring revenue, which most pre-seed and seed startups do not. At that stage negative margin is the right call because you are spending to find the market, so the rule would penalize correct behavior. Wait until you are scaling a proven model before you steer by it.
Which margin should I use for Rule of 40?
EBITDA margin and free cash flow margin are the two most common and the most honest, because they capture whether the business actually generates cash. Avoid using gross margin, since it ignores sales, marketing, and overhead and will make a cash-burning company look like it passes. Whatever you pick, keep it consistent across quarters.
Rule of 40 vs LTV:CAC ratio, which matters more?
They answer different questions. LTV:CAC tells you whether a single customer is profitable to acquire, while Rule of 40 tells you whether the whole company is balancing growth and profit. A founder should watch LTV:CAC first to confirm the unit economics work, then use Rule of 40 to check that the company-level mix is sustainable as you scale.
Can a company beat Rule of 40 and still be unhealthy?
Yes. A one-time event like a deferred expense, a large lumpy contract, or a round of layoffs can inflate the score for a quarter without the underlying business improving. The number is only useful as a trend, so look at it over four or more consecutive quarters and pair it with retention and burn so a single good period does not fool you.
Related terms
More in Unit Economics
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Last updated 2026-06-09 · Back to the glossary