Most owners can recite their gross margin but not their CAC. That’s the gap that kills marketing budgets. This post is the napkin math every owner should be able to do without opening a spreadsheet.
The three numbers that matter
CAC: the napkin version
Total marketing spend in a quarter ÷ new customers in that quarter. Don’t fight over what counts as “marketing spend” — include everything: ads, agency fees, the part-time social hire, the free trials you gave away. If it bought a customer, it counts.
LTV: the version you can compute today
Average order × gross margin × purchases per year × years retained. For services businesses, “purchases per year” is usually 1 and “years retained” is 1.5–4. For product, multiply order value by repeat rate.
- $8,000 service × 60% margin × 1 purchase × 2.5 years = $12,000 LTV.
- $80 product × 50% margin × 3 purchases × 1.5 years = $180 LTV.
The ratio that tells you if marketing is “working”
LTV ÷ CAC. The benchmarks are simpler than people pretend:
- Below 1×: you’re losing money on every customer. Stop.
- 1×–2×: survival mode. Either lower CAC or raise LTV before scaling.
- 3×: standard SMB target. Healthy.
- 5×+: you’re leaving growth on the table. Spend more.
Payback: the cash flow constraint
Even at a great LTV/CAC ratio, payback can kill you. If you spend $400 to acquire a customer and they pay you back over 18 months, you need 18 months of working capital to scale. If they pay you back in 2, you can press the gas now.
“Our LTV/CAC was 4.2×. We thought we were healthy. We weren’t — payback was 14 months and we ran out of cash trying to triple-down. The lesson: ratio without payback is a lie.”
— Founder, $2.1M B2B SaaS
How to move each lever (in order of effort)
- Raise prices. Free, instant, biggest impact on LTV. Most SMBs are 15–25% under-priced.
- Re-segment. Cut your bottom-quartile customer profile from your ad targeting. CAC drops, LTV rises.
- Shorten payback. Add an upsell or annual prepay discount. Cash unlocks scale.
- Lower CAC. Last lever — usually requires more time and creative ammunition than owners expect.
The 60-second napkin test
Pull out a napkin (or your notes app). Write down:
- Q4 marketing spend, all-in: ____
- Q4 new customers: ____
- CAC: ____
- Avg LTV (use the formula above): ____
- Ratio: ____
If you can’t fill in the first two from memory, your CAC problem is actually a tracking problem.
Want this applied to your business?
Book a Free 20-min audit. We’ll do the napkin math live with your numbers and tell you the one lever that’ll move it most. Pick a time.