How this instrument works
The Rule of 40 score is a single number built from addition, not a ratio or a weighted average: take the year-over-year revenue growth rate, take the profit margin for the same period, and add the two percentages together. That plain-sum shape is deliberate. It treats a point of growth and a point of margin as worth the same to the score, which is what lets a fast-growing company still losing money and a slower, already-profitable one land on the same scale and be compared directly.
The score circulates most in venture capital and growth-equity conversations about subscription software businesses — a board deciding whether this quarter's numbers still look healthy, an investor screening a batch of companies before a deeper look, a SaaS CFO benchmarking against public comps before a fundraising round. None of those readers are asking whether the company is profitable in isolation; they are asking whether growth and profit together clear a bar that experience says separates durable subscription businesses from ones burning cash without enough growth to justify it.
Addition also means the arithmetic cannot tell two very different companies apart once their totals match. A business at 45% growth and 0% margin and one at 5% growth and 40% margin both score 45, despite carrying different risk, different capital needs, and different odds of surviving a slowdown. The formula does not know which margin definition fed it either — net profit, EBITDA, or free cash flow all plug in the same way, and the choice can move the result by ten points or more.
- Enter YoY revenue growth, % — the year-over-year revenue growth rate for the period being scored.
- Enter Profit margin (or FCF margin), % — pick one margin definition and hold it steady across any comparison; a negative figure is valid input.
- Read Rule of 40 score, which updates as either figure changes above.
- Compare the score against 40, the threshold most often cited as the bar for a healthy subscription business.
- Re-enter the margin using a different definition — gross, EBITDA, or free cash flow — to see how much that choice alone shifts the score.
Worked example — 30% growth, 15% margin
A subscription company grows revenue 30% year over year and posts a 15% profit margin (or FCF margin, if that is the figure the board tracks) over the same period. Feeding those two numbers into the formula gives 30 + 15 = 45 for the Rule of 40 score, five points clear of the 40 line commonly treated as the bar for a healthy SaaS business.
That same 45 could just as easily come from a company growing 45% a year at break-even margin, or one growing only 5% with a 40% margin — the addition makes no distinction between those very different businesses once their totals match. That is exactly why a board or investor reading a 45 still asks to see the growth rate and the margin separately before treating the combined score as the whole answer.
Questions
Where does the 40 threshold actually come from?
No regulator or accounting standard sets it. The number spread through venture-capital and growth-equity circles as an informal benchmark after investors noticed that well-regarded public SaaS companies tended to cluster near a combined growth-plus-margin score of 40. It works as a rule of thumb calibrated against a peer group, not a fixed law, and different investors cite slightly different cutoffs.
Does margin have to mean net profit margin?
No — growth is almost always year-over-year revenue growth, but the margin half is negotiable by convention. Some use net profit margin, others EBITDA margin, and many SaaS boards prefer free-cash-flow margin because it reflects the cash the business is actually generating or burning. Swapping the definition on an unchanged company can move the score by ten points or more, so any comparison across companies only holds if both used the same margin.
Can a company pass with a negative profit margin?
Yes, by design. A company growing 60% a year with a −20% margin scores exactly 40, because fast unprofitable growth and slower profitable growth are treated as interchangeable inputs to the same sum. Investors reading the score still look at the growth-and-margin split underneath it, since a business burning cash to fund growth carries different risk than a profitable one at the same combined total.
Is a higher score always better?
Generally, but a score built from two very different-stage companies proves little by itself. An early-stage company posting 150% growth on a small revenue base and a mature company posting 20% growth with a 25% margin can both clear 40 comfortably while facing entirely different risks and funding needs. The score reads best next to the growth and margin figures it was built from, not as their replacement.
How is this different from checking profit margin alone?
A profit margin figure on its own says nothing about growth, so two companies with an identical 20% margin — one shrinking, one doubling — look the same on that figure alone. The Rule of 40 score folds a growth rate into the profitability figure so a fast-growing unprofitable company and a slow-growing profitable one can sit on the same scale, at the cost of losing the detail either number carries by itself.
Does the score account for company size or industry?
No — it only adds two percentages, whether the business is a two-person startup or a public company with a billion dollars in revenue, and it was built around subscription software specifically, where high gross margins make trading growth for profit a meaningful choice. Applying the same 40 threshold to a lower-margin hardware or services business stretches the benchmark past the setting it was calibrated for.
References
- U.S. Securities and Exchange Commission — Beginners' Guide to Financial Statements
- U.S. Small Business Administration — Grow your business guide
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.