Both metrics grade the same spend against the same revenue. Sales efficiency states the result as a ratio of ARR to spend. CAC payback states it as a number of months until gross profit recovers the spend. Neither is more correct, and they answer different operating questions.
The two formulas
``` Sales Efficiency = Net New ARR / Sales and Marketing Spend CAC Payback Months = CAC / (New MRR x Gross Margin) ```
Efficiency is dimensionless and comparable across segments. Payback is denominated in time and comparable against runway.
Worked example
A company adds $6M net new ARR on $8M of go-to-market spend at 75% gross margin.
| Metric | Calculation | Result |
|---|---|---|
| Sales efficiency | $6M / $8M | 0.75 |
| Gross-margin-adjusted efficiency | ($6M x 0.75) / $8M | 0.56 |
| CAC payback | 12 / 0.5625 | 21.3 months |
When each metric misleads
Efficiency without gross margin. A top-line ratio treats a dollar of ARR at 60% margin the same as a dollar at 85%. Two companies with identical efficiency can have payback periods a year apart. Payback without contract terms. Monthly billing and annual prepay produce the same payback on paper and completely different cash positions. Payback assumes revenue arrives evenly. Both without churn. If a cohort churns before payback completes, the acquisition never recovered. Read either metric next to net revenue retention or you are measuring acquisition of revenue you did not keep.The input both depend on
Each metric divides by a revenue number that is a forecast until the period closes, and forecast revenue skews optimistic. ORM data shows that roughly 20% of the pipeline carrying in-quarter close dates on day one of the quarter closes in that quarter. Efficiency and payback both calculated on the fuller number will revise at quarter end, in the same direction, at the same time.
That is the argument for grading both metrics on booked ARR rather than expected ARR, and for tracking them on a rolling basis. See forecast accuracy for how to check whether the revenue side of either ratio can be trusted, and how to forecast revenue for the underlying method.
Frequently Asked Questions
Are sales efficiency and CAC payback mathematically related?
They are close to reciprocal once you adjust for gross margin. A gross-margin-adjusted efficiency ratio of 1.0 corresponds to roughly twelve months of payback, and 0.5 corresponds to roughly twenty-four. They diverge when contract terms, billing timing, or expansion treatment differ between the two calculations.
Which one should a board see?
Show CAC payback when the question is cash and runway, since payback is denominated in months and maps to burn. Show sales efficiency when the question is whether to add or move go-to-market spend, since the ratio compares cleanly across segments and channels.
Why can payback improve while efficiency worsens?
Payback uses gross profit, so a pricing or hosting change that lifts gross margin shortens payback without any change in bookings per dollar of spend. Efficiency uses top-line ARR and would not move. Check gross margin before crediting a payback improvement to the sales team.
Put these metrics to work
ORM builds custom revenue forecast models that turn concepts like sales efficiency vs cac payback period into prescriptive action for your team.
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