A 6-month CAC payback isn't a target — it's a debt covenant.

The "CAC payback under 12 months" rule of thumb gets repeated like gravity. For venture-backed B2B SaaS, it's too lax. Here's the math and the cohort instrumentation that surfaces the real number.

Most growth dashboards report blended CAC payback as a single number, monthly. Eight months. Eleven months. The board nods and moves on. But blended payback is the average of a distribution you've never inspected, and the average is hiding the fact that your worst-performing channel is paying back in 26 months while your best channel pays back in 4.

Why the 12-month rule is too generous

The 12-month payback heuristic was born in a 0% interest rate world where SaaS retention curves were forgiving. In 2026, with capital costing 8-12% and gross retention sitting at 88-92% for mid-market B2B, every additional month of payback compounds the cash drag. A 12-month payback at 90% gross retention means you're underwater on 10% of acquired customers at month 12.

The right way to think about it: payback isn't a target, it's a covenant on your cash burn. Once you frame it that way, you start asking the right question — "what is the longest payback I can absorb given my cash runway?" — instead of the wrong one — "what is industry average?"

Cohort instrumentation that surfaces the real number

You need three views the second your pipeline crosses €1M ARR:

Channel × month cohort — payback for each channel by month of acquisition. Surfaces channel decay before it shows up in blended.
Plan × month cohort — same axes, segmented by initial plan. Reveals when a plan you sell heavily has worse unit economics than the cheaper plan you de-prioritise.
Self-serve vs sales-led cohort — payback differs by acquisition motion in ways that are systematically under-reported. A 10-month self-serve payback is exceptional; a 10-month sales-led payback is a problem.

What to do when payback exceeds your covenant

Three levers, in order of speed:

Re-allocate spend within channels: the bottom 30% of campaigns usually accounts for 50% of payback drag. Cut them.
Re-price the lowest plan up by 15-20%. Conversion drops less than the math suggests because price-sensitive buyers were already churning.
Move acquisition cost from sales to lifecycle. Activation improvements compound; new acquisition doesn't.

The board cares about ARR. The CFO cares about payback. Until you've instrumented payback at cohort grain, the CFO is reading tea leaves.

If you want a half-day audit of your current CAC payback instrumentation — talk to us.