For years, the Rule of 40 has been the shorthand every software investor reaches for. Add revenue growth to profit margin. Clear 40 and the business is treated as having found a decent balance between investing for the future and earning money today.
The simplicity of it is why it caught on, even though it says nothing about how much of last year’s revenue is retained.
A company can report strong growth and attractive EBITDA while losing a meaningful portion of its customers. New sales may conceal that weakness temporarily, but the company has to replace lost revenue before it can create net growth.
This breakdown mattered less when buyers were paying up for growth. Now retention is a core valuation pillar and a gate to nearly every investment decision.
Gross dollar retention is the missing variable
Gross dollar retention (GDR) measures the recurring revenue that remains after customer churn and contraction, before expansion revenue is counted. Unlike net retention, it can’t be rescued by upselling a small number of successful customers.
A company with 85% GDR loses 15% of its revenue base each year. It begins every period with a significant hole that must be filled before new bookings produce any growth. A company with 95% GDR only loses 5% of its revenue base. More of its sales capacity can be directed toward compounding the business rather than rebuilding what disappeared.
The Rule of 40 can treat those companies as equivalent when their reported growth and margins are equal. But they aren’t the same. One owns a durable recurring-revenue base. The other is just treading water.
A better framework: The Staying Power Test
A more useful software screening metric combines the three components of durable value: revenue growth, EBITDA margin, and gross dollar retention. The test runs in two stages: a pass/fail gate on retention and then a score for the companies that clear it.
EquivalentRevenue growth + EBITDA margin − Gross revenue churn
Every point of recurring revenue lost reduces the score by one point. Retention isn’t just another positive operating metric. Churn is treated as a direct claim against the growth and profitability the company reports.
Why is that better than the Rule of 40? Growth and churn are both measured as points of recurring revenue. A company growing 20% while losing 12% of its base sold 32 points of new revenue to show 20. The Rule of 40 credits the 20 and never mentions the 12 it had to rebuild first. Measuring on gross retention is deliberate here too. Net retention lets expansion in a few large accounts paper over churn everywhere else.
Stage one: The 90% durability gate
The formula doesn’t let extreme growth or profitability compensate for weak retention. Below 90% GDR, the practical threshold for a healthy recurring-revenue business, a company fails the initial screen regardless of its calculated score.
A company below 90% GDR is losing more than one-tenth of its existing recurring revenue each year. That level of leakage raises questions about product necessity, customer satisfaction, competitive pressure, and the cost required to sustain growth.
The first stage of the test is therefore binary:
- GDR of at least 90%: the company passes the retention gate and receives a score.
- GDR below 90%: the company is not scored because the recurring-revenue base is deteriorating too quickly.
Stage two: Scoring against the Rule of 30
Companies that pass the retention gate are evaluated using the Staying Power Test. A score of 30 or higher indicates an attractive balance of growth, EBITDA, and revenue durability.
Consider a representative high-quality software business:
The calculation is 15 + 25 + 90 - 100 = 30.
The company produces 40 combined points of growth and profitability, then loses ten points because 10% of its recurring revenue must be replaced each year. That is why the Rule of 40 becomes the Rule of 30.
The same Rule of 40 can hide radically different businesses
Consider three companies that all produce 40 combined points of growth and EBITDA:
Under the traditional Rule of 40, all three companies appear equal. But the durability framework reaches a different conclusion.
Company A is growing rapidly, but it loses 18% of its existing revenue each year. Its sales organization must replace nearly one-fifth of the revenue base before producing net growth. Despite its headline score, it fails the retention gate.
Company B combines moderate growth with meaningful EBITDA and 90% GDR. Its score of 30 indicates a balanced, credible software asset.
Company C produces the same combined growth and EBITDA as the other two companies but retains 97% of its revenue. Its growth is more likely to compound and its margins are less exposed to the cost of repeatedly reacquiring lost revenue.
The traditional formula sees three Rule of 40 businesses. The Staying Power Test reveals one fragile asset, one good asset, and one premium asset.
Why retention changes the meaning of growth
Gross retention affects nearly every component of software value. Weak retention reduces revenue visibility, increases the burden on customer acquisition, and raises the risk that growth will disappear when new bookings weaken.
Strong retention allows revenue to compound. It gives management more flexibility to reduce sales spending without causing contraction. It also strengthens an acquirer’s downside case because slower new sales are less damaging when most existing customers remain.
This is why moderate growth can be more valuable than aggressive but fragile growth. A company growing 15% to 25% with high retention and a 20% to 30% EBITDA margin gives a buyer multiple ways to create value. The buyer can collect cash, reinvest selectively, support leverage or fund acquisitions without requiring every future assumption to be correct.
A high-growth business with weak retention and cash burn offers a narrower path. Growth must continue, acquisition efficiency must improve, margins must appear, and the terminal valuation must remain supportive.
A screen, not a substitute for underwriting
The Staying Power Test is an opening screen, not a complete valuation model. Investors still need to understand customer concentration, gross margins, sales efficiency, free-cash-flow conversion, capitalized development costs, and the investment required to maintain the product.
They also need to assess whether the company’s retention is durable. High historical GDR is valuable evidence that customers still view the product as necessary, but it doesn’t guarantee protection from future competition or technological disruption.
The test improves on the Rule of 40 because it forces growth and profitability to overcome the cost of churn. It rewards growth, but not growth that merely replaces lost customers. It rewards profitability, but not profitability generated while the recurring-revenue base quietly deteriorates.
The defining characteristic of a recurring-revenue business is not that it can grow by finding new revenue. It is that the business can keep it.