How the calculation works
CAC = sales & marketing spend ÷ new customers won in the same period. Monthly gross profit per customer = (ACV × gross margin %) ÷ 12. Payback months = CAC ÷ monthly gross profit. The result tells you how many months of gross profit it takes to repay what you spent to win a customer.
Two numbers quietly distort most teams' payback: undercounted CAC (forgetting loaded salaries, tools, and agency fees) and overstated gross margin (ignoring implementation services and third-party pass-throughs). Use a clean, fully loaded quarter and the number gets honest.
A worked example
A company spends $240,000 on sales and marketing in a quarter, fully loaded, and wins 20 new customers. CAC is $240,000 ÷ 20 = $12,000. Those customers pay $24,000 a year at an 80% gross margin, so each one returns $24,000 × 0.80 ÷ 12 = $1,600 of gross profit a month. Payback is $12,000 ÷ $1,600 = 7.5 months.
Drop the gross margin from that calculation and the answer becomes $12,000 ÷ $2,000 = 6 months. The difference is not rounding. Revenue does not repay acquisition cost, gross profit does, so a payback figure built on revenue is short by exactly the margin it ignored.
Two versions of the formula, and when each one is right
Per customer, which is what this calculator runs: CAC ÷ (ACV × gross margin ÷ 12). It is the clearer one to explain and the right one when your customers pay roughly the same amount.
From new ARR: sales and marketing spend ÷ (new ARR × gross margin) × 12. Same example: $240,000 ÷ ($480,000 × 0.80) × 12 = 7.5 months. The two agree whenever every new customer has the same ACV. When they do not, use the new-ARR version, because an average ACV hides the mix. Ten $5,000 customers and one $200,000 customer average out to a contract nobody actually signed.
Whichever you use, hold two things fixed across periods: what counts as sales and marketing cost, and whether expansion revenue from existing customers is included in the denominator. Most teams exclude it, since expansion was not bought by the new-logo spend. Changing either one between quarters will move the number more than any real improvement.
How to read the benchmark
The 6 to 12 month band on this page is a target, not the typical result. Benchmarkit's 2025 B2B SaaS Performance Metrics report put median CAC payback at 18 months for calendar 2024, with the middle half of its sample between 12 and 24 months (N=148). If your number lands at 15, you are close to the middle of the market. Whether that is acceptable depends on your cash runway and retention, which is what the CAC payback period guide works through.
If your payback is too long
Cutting spend rarely fixes payback — it compresses the numerator without touching the broken driver. The fastest, most durable levers are raising ACV (higher tiers, annual prepay) and protecting gross margin (services, pass-throughs, discount discipline), followed by structurally reducing CAC in the funnel.