CAC payback answers a simple question: after you win a customer, how many months until the gross profit from that customer repays what it cost to win them? It is one of the clearest measures of sales efficiency, and one of the easiest to flatter.
The formula
CAC payback (months) = sales and marketing spend in the period ÷ (new ARR from new customers in the period × gross margin ÷ 12)
Example: $900,000 of sales and marketing spend in a quarter, $1,200,000 of new ARR, 78% gross margin.
- Monthly gross profit from new ARR: $1,200,000 × 78% ÷ 12 = $78,000
- CAC payback: $900,000 ÷ $78,000 = about 11.5 months
Getting the inputs right
- Sales and marketing spend comes from the ledger: salaries, commissions (as paid), benefits, payroll taxes, advertising, events, tools, agencies, and the share of rent and IT those teams use. Department tagging in the accounting system makes this a report instead of an estimate.
- New ARR comes from the ARR bridge. Decide whether expansion is in or out and stay consistent; many companies show CAC payback on new logos and a separate efficiency metric that includes expansion.
- Gross margin should be subscription gross margin, not blended with services.
- Lag. Spend this quarter often produces bookings next quarter. A one-quarter lag on spend gives a truer picture for longer sales cycles.
Traps
- Excluding salaries and counting only paid media.
- Using revenue instead of gross profit.
- Counting expansion as new ARR without saying so.
- Using capitalized commission expense instead of cash commissions paid.
- Averaging across segments with very different economics. SMB and enterprise motions deserve separate paybacks.
Using it
Payback is most useful as a trend by segment and channel. Rising payback means each new dollar of ARR is getting more expensive, which feeds directly into burn multiple and runway.
We calculate CAC payback quarterly from department-tagged ledger data and the ARR bridge, by segment where the data supports it, and show it next to burn multiple and NRR in the finance pack.
A worked example by segment
Blended numbers hide the decisions. Splitting the same quarter by motion shows where the next dollar should go:
| Segment | S&M spend | New ARR | Gross margin | CAC payback |
|---|---|---|---|---|
| Self-serve | $150,000 | $360,000 | 80% | about 6 months |
| Mid-market | $450,000 | $600,000 | 78% | about 11.5 months |
| Enterprise | $300,000 | $240,000 | 75% | 20 months |
The blended payback looks acceptable; the enterprise motion on its own does not, at least not yet. That is a hiring and territory decision the board should see, not average away.
Allocating shared costs
Marketing programs, brand spend and sales tools serve every segment. Allocate them with a documented rule (pipeline generated, opportunities created or headcount) and keep the rule stable from quarter to quarter. Changing the allocation method makes payback move for reasons that have nothing to do with performance.
Companion metrics
- Magic number: net new ARR in a quarter divided by the prior quarter's sales and marketing spend. A quick read on whether to step on the gas.
- LTV to CAC: lifetime gross profit of a customer divided by CAC. Useful, but lifetime assumptions are fragile for young companies; payback is easier to defend.
- Burn multiple: the company-wide version of the same question, including every function, not just go-to-market.
Checklist before you show it
- Department tags in the ledger are complete for the period.
- Commissions are on a cash-paid basis for this calculation.
- New ARR matches the ARR bridge.
- Gross margin is subscription margin.
- The lag assumption is stated on the slide.
Sources
Questions founders ask
Should CAC include salaries?
Yes. Fully loaded CAC includes sales and marketing salaries, commissions, benefits, tools, advertising and the share of overhead those teams use.
Why use gross margin in the formula?
Because a dollar of revenue is not a dollar available to repay acquisition cost. Hosting, support and onboarding consume part of it first.
