SaaS Metrics: ARR, Net Revenue Retention and CAC Payback
A subscription business can grow reported revenue while quietly rotting from customer churn, so investors lean on three numbers — ARR, net revenue retention, and CAC payback — that GAAP income statements don't show directly.
A subscription software company can report growing revenue for years while its actual product is quietly losing customers, as long as new sign-ups keep outpacing the ones walking out the door. GAAP revenue recognition doesn't distinguish "revenue from customers we kept" from "revenue from customers we just replaced the ones who left" — so SaaS investors built a separate set of metrics specifically to see through that.
ARR tells you the size of the recurring revenue engine. Net revenue retention tells you whether existing customers alone are growing or shrinking, with new sales stripped out entirely. CAC payback tells you how long it takes a new customer to earn back what it cost to acquire them. Together they answer: how big is it, is it healthy from the inside, and is growth actually profitable.
The three numbers
Annual Recurring Revenue (ARR) is simply the current annualized value of all active subscription contracts — not GAAP revenue, which recognizes contracts ratably over time, but a snapshot of "if nothing changes, this is next year's recurring revenue run-rate."
Net Revenue Retention (NRR) measures what happens to a fixed cohort of existing customers over a year, with new customers excluded entirely:
In words: take last year's existing customers, add whatever they spent more on (upsells, seat growth), subtract whatever they spent less on or cancelled entirely, and compare the result to where they started. A figure above 100% means existing customers alone are growing the business even before a single new logo is signed.
CAC Payback Period measures how many months of a new customer's gross margin it takes to recover what was spent acquiring them:
In words: divide the sales and marketing cost of landing one customer by the monthly gross profit that customer generates — the answer is how many months pass before that customer has paid for their own acquisition.
Worked example
A company starts the year with $20 million ARR from existing customers. Over the year those same customers add $4 million in upsells, but $1 million downgrades and $5 million churns away entirely.
NRR = ($20m + $4m − $1m − $5m) / $20m = $18m / $20m = 90%. Existing customers alone shrank by 10%. If new sales added $8 million of fresh ARR, total ARR still grew from $20m to $26m — a healthy-looking 30% growth rate that hides a customer base leaking value.
Separately, this company spends $15,000 in sales and marketing to land a customer paying $1,000 a month, with an 80% gross margin. Monthly gross profit per customer = $1,000 × 0.80 = $800. CAC payback = $15,000 / $800 ≈ 18.75 months — over a year and a half before that customer has paid back their own acquisition cost, a long payback that only works if NRR is high enough to keep that customer for years.
What this means in practice
An NRR comfortably above 100%, paired with a CAC payback under roughly 18 months, is the classic signature of an efficient, compounding SaaS business; either number moving the wrong way is an early warning long before it shows up in GAAP revenue.
Rising ARR alongside falling NRR is one of the most common SaaS red flags: it means the company is spending increasing amounts of CAC just to replace customers it's losing, not to grow. Never read ARR growth as good news without checking NRR alongside it.
Further reading
- Meritech Capital / Bessemer, State of the Cloud reports