What it is
CAC is what you spend in sales and marketing to acquire a customer (or a dollar of new ARR). The label is useless without the formula — fully loaded vs paid media only changes the story.
How it’s calculated
Period S&M spend ÷ new customers (or ÷ new ARR). State whether CS or outbound SDRs are included, and whether expansion is in the denominator.
Where it breaks
CAC breaks when organic and paid mixes shift silently, when partner-sourced deals are excluded inconsistently, or when LTV:CAC uses mismatched cohorts.
In the board pack
Publish the CAC formula next to payback and LTV. Efficiency slides without definitions invite diligence pain.
Keep the written definition stable across close, the board pack, and diligence so the same word never means two math models.
When this metric moves, point to the source schedule and the bridge components — not a screenshot from a private workbook.