Payback (months) = CAC ÷ (monthly ARPA x gross margin %)
The question it answers is not "is this profitable" but "how long is our money somewhere else".
Why margin, not revenue
Revenue-based payback ignores the cost of serving the customer during the payback window, and that cost is real. At 75% gross margin, a revenue-based payback understates by a quarter.
Same cost-of-revenue definition as gross margin, or the two numbers argue.
It matters more than the CLTV ratio
CLTV to CAC says the economics eventually work. Payback says whether you can fund the gap until they do.
Two businesses, both 3:1:
- 8-month payback: growth largely self-funds. Faster acquisition is affordable.
- 26-month payback: every new customer consumes cash for over two years.
Growth requires financing, and a downturn is dangerous.
The ratio ranks these identically. Payback separates them, and payback is the one that determines whether the company survives a bad year.
What moves it
In order of use:
- Price. A direct multiplier on the denominator, and the fastest lever.
- CAC. Better targeting lowers it more reliably than better closing does.
- Gross margin. Slow to move and usually structural.
- Time to first value, if billing starts on activation rather than signature.
Notably absent: churn. Payback ignores it entirely, which is the metric's own blind spot. A 6-month payback on customers who leave at month 9 is not a business.
A worked example
Fully loaded CAC of $11,400. ARPA $9,600 a year, so $800 a month, at 76% gross margin.
Monthly margin = 800 x 0.76 = $608
Payback = 11,400 ÷ 608 = 18.8 months
Under 12 months is generally considered strong for B2B software, 12 to 18 workable, and beyond 24 a financing question rather than an operating one. Those bands are convention, not law.
Segment it
Self-serve payback of 4 months and enterprise payback of 24 months blend to a figure describing neither. Worse, the blend moves with mix, so a good self-serve quarter can make enterprise payback appear to improve while it worsened.
The traps
- Revenue instead of margin.
- Programme-only CAC.
- Blending segments.
- Ignoring churn inside the payback window, which is the metric's structural
blind spot.
- Comparing to a benchmark without matching the CAC construction.
Where this sits
Payback is Measurement in the Tenbound Pipeline Architecture Standard, and it is the metric a pipeline team most directly influences: every improvement in targeting at Market and qualification at Motion lowers CAC, which shortens payback proportionally.