From Startup Fortune · · 2m
How to Calculate SaaS CAC Payback Period
SaaS founders often miscalculate payback periods by ignoring gross margin, risking cash flow and investor trust.
In brief
SaaS founders often miscalculate payback periods by ignoring gross margin, risking cash flow and investor trust. SaaS founders must use gross margin in CAC payback calculations to avoid underestimating true payback periods and cash runway. Originally reported by Startup Fortune.
CAC Payback Period Misconception
Founders obsess over CAC and LTV but blow the payback period by forgetting gross margin and non-sales costs eat into it.
The Math Error
A $12,000 CAC and $1,000 monthly revenue looks like a 12-month payback but at 70% gross margin it's really 17 months.
Bessemer and OpenView Benchmarks
Bessemer and OpenView both put healthy SaaS payback under 18 months with best-in-class companies under 12 months.
The Gross Margin Multiplier
The formula is CAC divided by (monthly revenue times gross margin percentage), not revenue alone.
Fully Loaded CAC
Start with fully loaded CAC: every dollar of sales and marketing spend including salaries, commissions, ad spend, and tools like HubSpot or Salesforce.
Gross Margin Calculation
Multiply average monthly recurring revenue per customer by gross margin percentage to get monthly gross margin dollars per customer.
Real Payback Period
Divide CAC by monthly gross margin dollars per customer: $10,000 divided by $560 equals 17.9 months.
Why the Error Matters
Using revenue instead of gross margin gives a false 12.5-month payback, making boards nod while ignoring real cash runway risks.
Bessemer's Perspective
Bessemer Venture Partners treats fully-loaded CAC as including onboarding, support, and hosting costs because companies leave them out.
SaaS Payback Benchmarks
Under 12 months is excellent, 12 to 18 months is healthy for mid-market B2B SaaS, and over 24 months starts to worry investors.
Rising Payback Period Warning
A rising payback period with flat CAC is usually an early warning sign of churn, not a sales problem.
Fixing the Calculation
Show the full calculation: fully loaded CAC, average revenue per customer, gross margin percentage, and the resulting payback period on the same slide.
The short version
SaaS founders must use gross margin in CAC payback calculations to avoid underestimating true payback periods and cash runway.
