Growth vs. profit

The Rule of 40, and what it actually looks like in a five-year model

By Assaf Schwartz · 10 September 2026 · 9 min read

The Rule of 40 is the most quoted number in SaaS and the most casually calculated. Two percentages, one addition, a bar to clear. What it actually encodes is an exchange rate between growth and profit — and whether that exchange rate is any good in your business depends on inputs the rule never mentions.

What the rule says

growth rate % + profit margin % ≥ 40. Both terms are annual, both are percentages, and the arithmetic treats them as interchangeable: a company growing 60% while losing 20% of revenue scores the same 40 as one growing 10% at a 30% margin.

That interchangeability is the whole idea. The rule exists to stop two arguments. It stops the fast-growing business claiming that losses do not matter, and it stops the profitable business claiming that stagnation is prudence. Below 40, you are neither growing fast enough to justify the burn nor profitable enough to justify the growth rate.

Two things it is not. It is not a valuation formula — it correlates with revenue multiples, but it is a screen, not a price. And it is not a target for an early-stage company: at $2M of ARR, growth is so much cheaper to buy than margin that almost any competent business clears 40 on growth alone, and almost any struggling one misses by fifty points. The rule earns its keep somewhere north of $10M of ARR, where both terms are genuinely in play.

Computing it from an annual row

The simulator's annual view gives you everything the calculation needs. Each row carries that year's revenue, its net profit and its ending ARR, so the score for a given year is two divisions.

Growth is year-over-year ARR: (ending ARR ÷ prior year ending ARR) − 1. Use ARR rather than recognised revenue if you have it. Revenue growth lags ARR growth by roughly half a year in a monthly billing business and by more in an annual one, so a company that decelerated in the second half will look healthier on revenue than it is.

Margin is that year's profit over that year's revenue: net profit ÷ revenue. Which profit line you use is the single largest source of disagreement in this calculation, and it is worth settling explicitly before anyone quotes a number — more on that below.

Year one has no prior year, so the first computable score is year two. That is not a limitation of the model so much as a property of the metric: a growth rate needs two observations, and comparing month twelve to a partial first year produces a number that means nothing.

The same company, year by year

Here is the default input set — $120,000 of starting MRR, 4.0% organic monthly growth, 2.8% monthly revenue churn, 8 engineers — scored on every year the model can score.

The company clears the bar exactly once, in year 5, at 41.9. It gets there the way real companies do: not by improving growth or margin in isolation, but by both improving together as fixed costs stop growing with revenue. Growth rises from 15.4% to 26.1% because re-invested profit compounds into acquisition, and margin rises from -3.0% to 15.8% because revenue grew 72% while the cost base grew far less.

Note what year 2 looks like: a score of 12.4, which is a clear fail on the rule, in a business that is perfectly healthy and will be fine three years later. This is why applying the rule to a company below scale produces bad decisions.

Five companies in year three

Scored in the same year, the five saved scenarios spread across nearly four hundred points. Year 3 is the fairest place to look: the terminal year of any five-year projection flatters compounding growth.

The bootstrapped scenario scores 67.4 on 29.2% growth and a 38.3% margin — the profitable end of the trade-off. The churn crisis scores -310.1, and both terms are negative, which is the only unambiguous reading the rule ever produces: revenue is shrinking and it is losing money doing it.

A trade-off, not a target

The rule is usually described as a bar to clear. It is more useful read as a statement about an exchange rate: you may convert a point of margin into growth, and the conversion is worthwhile only if you get more than a point back. Whether you do is decided by CAC payback, not by the rule.

Take the default company and move Re-investment rate — the share of operating profit pushed into acquisition — at two different acquisition costs. At $3,600 CAC a customer pays back in 11 months. At $14,400 the same customer takes 44.

With an efficient acquisition motion the trade is strongly positive: moving from 0% to 90% re-investment costs 12.6 points of margin and buys 65.1 points of growth, taking the score from 31.9 to 84.4. With the expensive motion the identical decision costs the same margin and buys only 7.4 points, and the score falls from 31.9 to 24.9.

That is the whole point of the rule, and it is invisible if you only look at the total. Two companies reporting 40 can be in opposite positions: one where every marginal dollar moved from profit to sales raises the score, and one where it lowers it. Before you decide to buy growth with margin, check what a customer costs and how long they take to pay for themselves.

Where the score gets faked

Annualising a monthly growth rate badly

This is the most common error and it is always in the flattering direction. A business adding 4.0% of new MRR a month does not grow 48% a year. Compounded, that rate is 60.1% — and net of 2.8% monthly churn, which is what actually lands in ARR, it is 15.4%. That is exactly the year-two ARR growth the model reports, 15.4%, and it is a third of the naive figure.

Choosing the profit line after seeing the answer

EBITDA, operating profit, net profit and free cash flow give four different scores for the same year. In year 5 of the default model, operating profit is $695,695 — a 22.5% margin and a score of 48.6 — while net profit, struck after the acquisition spend that operating profit funds, is $486,987, a 15.8% margin and a score of 41.9. Same year, same company, 6.8 points apart. Free cash flow is the honest default because it is the line that cannot be adjusted; if you use EBITDA, say so every time.

Ignoring gross margin entirely

The rule has no gross margin term, which quietly makes it unfair to compare a software business with a services-heavy one. Run the default company at three different Gross margin settings and the year-5 score moves by more than thirty points without a single change to growth strategy or headcount.

Reading one year as a trend

A single score is a snapshot of a company at a point on its cost curve. The default company scores 12.4 and 41.9 in the same five-year run without anything changing about the business. Report the series.

Using it in a five-year model

Three habits make the rule useful rather than decorative when you are building a plan.

• Score every year, and look at the slope. The default company's series is 12.4, 20.5, 30.6, 41.9: operating leverage arriving. A plan that runs the other way, starting in the forties and drifting down four points a year, is buying its growth at a worsening price, and the total will look respectable for two more years while it does.
• Put the cash line next to it. The score has no denominator in dollars. Show ending cash and minimum cash beside every year, or you will approve a plan that clears 40 and runs out of money, as the seed-stage scenario above does.
• Sanity-check it against burn multiple. The two disagree in exactly one interesting case: high growth bought expensively. A plan scoring well above 40 on growth while its burn multiple sits above 2x is spending capital to make the score, and the score is not the thing you are trying to maximise.

The honest summary: the Rule of 40 is a good screen and a poor objective. It tells you whether the combination of growth and profitability you have chosen is defensible. It does not tell you whether the trade you are about to make is a good one — for that, see burn multiple, which prices the growth you are buying, and CAC payback vs. LTV:CAC, which tells you how long you finance it.

Educational content, not financial advice. Figures here are illustrative and exclude taxes, financing and one-off items. Model your own numbers in the simulator and check them with a qualified accountant before acting.