Is our CAC sustainable?

Why is the number alone useless?

Because the same CAC is healthy for one business and fatal for another, and nothing on the CAC figure tells you which you are. £85 is comfortable if each customer brings £400 of durable revenue and frightening if they bring £120 and churn in a year. Sustainability lives in the relationship, not the number, and the relationship needs a rule you set for what ratio you can bear.

So passing a CAC figure around a team guarantees disagreement: each person silently applies their own rule of thumb, and the conversation is really a clash of unstated standards. The figure was never the disagreement; the missing shared rule was.

What does the verdict measure against?

Say you're running a subscription business, and you ratified the rule you actually steer by: CAC must stay under a third of first-year revenue per customer, because above that new growth stops self-funding and starts drawing down the cash you are protecting. Read against it: “not sustainable — CAC is £85 against £240 first-year revenue, a 35% ratio past your one-third line, so this cohort of growth is eating cash rather than funding itself.”

The one-third rule and the self-funding reasoning are your decision, and they are what make £85 mean something. A model can report the CAC and even the ratio; it cannot call it unsustainable, because the line that defines sustainable is yours, not the data’s. The frame judges the data it is given; it does not verify the source’s accuracy.

What does a verdict unlock?

A decision instead of a discussion. “Not sustainable, ratio 35% against your one-third line” points straight at the levers — lower CAC or raise first-year revenue — and gives a target for each. And when Noor raises prices and first-year revenue climbs, the same £85 CAC may pass the rule without any change to acquisition; the read re-judges it against the new economics automatically.

So “is our CAC sustainable” stops being a figure that starts an argument and becomes a verdict that ends one — because the rule that decides it finally travels with the number.

A CAC figure is neither sustainable nor not until it meets the ratio your model can bear; measured context holds the CAC-to-new-revenue rule you ratified and returns a yes-or-no verdict with the reasoning, so the number stops starting arguments and starts ending them.

Reads through Unl arrive with measured context — in the presence of the decisions you’ve already settled. The reach lane is live: one box, paste anything. If it speaks MCP, Unl can reach it. Readings arrive unprompted, the data beside the criterion; Unl is a courier, not a warehouse, and keeps only your keys and the frame.

Read further

• The channel-budget meeting, through Unl
• Should I raise or cut the paid budget?
• Is this channel scaling or saturating?
• Does the data meet our criteria?