What Is the Rule of 40, and Does It Apply to a Small Business?

The Rule of 40 adds your revenue growth rate to your profit margin and asks for 40. Hit it, you pass. It came out of software investing, popularized by Brad Feld in 2015 as a test for SaaS companies at roughly $50 million in revenue and up. There, a growth dollar and a margin dollar trade one for one. In a $1-5M service business they don't trade, so the number flatters you or scares you. It rarely informs you.

What is the Rule of 40, exactly?

One line of arithmetic. Take year-over-year revenue growth as a percent, take profit margin as a percent, add them. 30 percent growth at a 10 percent margin scores 40. So does 10 percent growth at a 30 percent margin. So does 50 percent growth while burning 10 percent, Feld's own example.

Scoring 40 was never the point. The trade was, and it's the first thing that stops working the moment you leave software.

A software company can grow slower and keep the margin, or spend the margin and grow faster, and the rule says pick either, the sum is what matters. Genuinely useful idea, when it holds.

Two definitions decide whether your score is 34 or 46 off identical books. Profit usually means EBITDA margin (earnings before interest, taxes, depreciation, and amortization, which strips out financing and depreciation choices but ignores working capital and equipment spending, so it is not a cash number). Sometimes free cash flow. Sometimes plain operating income. Growth means recurring revenue in some hands, total revenue in others. Pick your two. Write them down. Never move them.

Why the rule works for software

Three assumptions sit underneath it, and they're load-bearing.

• Revenue renews without being resold. A dollar of new subscription revenue is close to an annuity. It's still there next year, minus churn and the cost of keeping those customers happy.
• Gross margin is high. Most public SaaS companies run gross margins above 70 percent, and about a quarter clear 80, so a growth dollar comes out of a deep pool.
• Growth spending is separable. Sales and marketing sit below the gross margin line, so cutting them lifts operating profit without touching how the product gets delivered.

That third one is the quiet one, and it's where small businesses get hurt. It's slower than the pitch even in software, because commissions you already paid keep amortizing against the contracts that earned them, so the relief shows up gradually rather than in a month. But it works. Pull the same lever at your shop and you still have delivery staff on payroll, still have work in progress, and now nothing feeding it. Your margin doesn't appear. Utilization collapses first, so the number gets worse before it gets better. Growth is a hire, not a budget line, and what a service business actually clears leaves far less room to spend a margin point into it.

Does the Rule of 40 apply to a $1-5M service business?

Mostly no. Not because you're too small. Because the trade the whole rule is built on doesn't exist inside your business.

Row three is the one that ruins the math quietly. Across ten years of cleanup work in construction, trades, hospitality, and professional services, owner pay routinely sits off market by roughly $60K to $150K in either direction, which moves the margin line several points on a $2M business before anything real has happened. Those are shapes I see in cleanup work, not a published benchmark.

Owner salary isn't the only line that isn't what it claims to be. The spouse on payroll who doesn't work there. The truck. The personal phone plan. The rent you pay your own LLC at a number you picked. The one-time legal settlement sitting in operating expenses. A buyer will argue every one of them with you, so settle how you take money out of the business before you score anything.

One caution, because this is the sentence with liability on it. Restating your pay to market is a valuation exercise: what it would cost to hire your replacement. S corp reasonable compensation is a different test, built on the services you personally perform, and it lands on a different number more often than not. Doing the first doesn't settle the second. Ask whoever files your return about that one.

Row five is the one that ends companies. The Rule of 40 explicitly blesses running at a loss if growth is fast enough, because in venture-backed software the loss is funded by investors who signed up for exactly that. Your loss is funded by your bank account and a line of credit that reprices when the bank gets nervous.

How do I run the number honestly?

There's a version worth running. Not as a grade, as a sanity check on whether your own numbers mean what you think they mean. Four corrections:

1. Normalize owner comp to replacement cost. What would it cost to hire someone to do your job? For a working owner of a $1-5M service firm, the engagements I see land in the $120K to $200K range depending on whether you sell, deliver, or just manage. Use that, recompute margin, and you've done the one adjustment that usually matters more than the other three combined.
2. Use trailing twelve months, not the calendar year. Not because twelve months average out differently (they don't), but because in October a calendar-year score is describing a period that ended ten months ago. TTM cures staleness, not smoothing.
3. Hold both definitions still across years. Growth measured on total revenue this year and recurring revenue last year isn't a trend. It's a coincidence.
4. Run it on the recurring slice only, if your book is mixed. Blending a $600K one-time build into a retainer base produces a score that describes a company which doesn't exist. The recurring-revenue metrics you already read monthly are the right denominators here.

What that does to a real set of books. Take a $2.4M professional services firm, up from $2.15M, so 12 percent growth. The owner pays herself $95K and rents the building she owns personally to the business for $2,000 a month. Illustrative numbers, but this is the shape I see constantly.

Same books. Same bank balance. Five points of score gone, and neither column is a lie. One of them describes what the business earns after paying a stranger to do the owner's job, and that's the only one a buyer or a lender will read.

Then treat the answer as a direction, not a grade. Scoring 31 two years running while your normalized margin climbs is a better business than scoring 44 on the back of one large client who signed in March.

What should I track instead at $1-5M?

Drop the sum and read the parts.

• Normalized profit margin, three years side by side. Same definition every year, owner comp restated, no add-backs you'd be embarrassed to explain out loud. Across the service engagements I see, a healthy net margin sits in the 10 to 20 percent range once the owner is paid a market salary, and under 10 usually means pricing is too low or you're absorbing hours nobody is billing. Practitioner range, not a published benchmark. The three-year trend is the real signal.
• Repeat revenue as a percentage of total. What share of this year's revenue came from customers who were already there last year? It answers the durability question the Rule of 40 only assumes. Below roughly 70 percent, a Rule of 40 score is noise.
• Whether the profit showed up in the bank. Compare operating cash flow to profit across the same period. A persistent gap is worth chasing, but don't assume it's collections. Unbilled work in progress, retainage, milestone billing, inventory, seasonal swings, and growth itself all consume cash inside a genuinely profitable business. Find the drawer it's sitting in before you blame anyone.

Nobody buying a $3M service business will ask your Rule of 40 score. They'll ask for normalized earnings, customer concentration, and whether the business runs without you, which is most of what actually makes a service business sellable.

The honest answer

When you ask about the Rule of 40, you're usually asking something more uncomfortable: am I growing fast enough to justify how little I'm making?

Fair question, wrong instrument.

The rule was built for companies that convert margin into growth at a fixed exchange rate and buy the loss with someone else's money. You can do neither. Your growth costs delivery capacity, your margin is a decision about your own paycheck, and your downside is personal. A borrowed benchmark answers a borrowed question.

Normalize your pay, hold your definitions still, and watch margin and repeat revenue move over three years. That tells you what you were actually asking.

Two numbers you can defend beat one you borrowed.