LTV:CAC is the single most important unit economics metric for subscription businesses. Investors use it as a quick filter — below 3:1, most won't engage further. Here's how to calculate it correctly and what the benchmarks mean.
The Correct Formulas
Customer Lifetime Value (LTV)
Simple formula: LTV = ARPU × Gross Margin % ÷ Monthly Churn Rate
Example:
- ARPU (monthly): $150
- Gross margin: 75%
- Monthly churn: 2%
- LTV = $150 × 0.75 ÷ 0.02 = $5,625
Customer Acquisition Cost (CAC)
CAC = Total Sales & Marketing Spend ÷ New Customers Acquired
Example:
- Monthly S&M spend: $50,000
- New customers this month: 25
- CAC = $50,000 ÷ 25 = $2,000
LTV:CAC Ratio
LTV:CAC = $5,625 ÷ $2,000 = 2.8:1 (below the 3:1 threshold)
Benchmarks by Stage
| Stage | Revenue | Acceptable LTV:CAC | Good LTV:CAC | Excellent |
|---|---|---|---|---|
| Pre-seed | < $500K ARR | 1-2x (proving model) | 3x | — |
| Seed | $500K-$2M | 2-3x | 3-5x | 5x+ |
| Series A | $2M-$10M | 3x | 4-6x | 7x+ |
| Series B | $10M-$50M | 3-4x | 5-7x | 8x+ |
| Growth | $50M+ | 4x | 5-8x | 10x+ |
The 3:1 threshold isn't arbitrary — at 3:1, a company earns $3 in gross profit for every $1 spent acquiring a customer, covering S&M costs with enough margin to fund other operations.
Common Calculation Errors
Error 1: Not applying gross margin
Wrong: LTV = ARPU ÷ Churn
Correct: LTV = ARPU × Gross Margin% ÷ Churn
Including gross margin matters because LTV represents profit contribution, not revenue. At 70% gross margin, you keep $0.70 of every revenue dollar.
Error 2: Not including sales team cost in CAC
Wrong: CAC = marketing spend only Correct: CAC = marketing spend + sales team fully-loaded cost + sales tools
For enterprise SaaS with a sales team, omitting sales headcount dramatically understates CAC.
Error 3: Using monthly averages incorrectly
If your sales cycle is 3 months and you closed 10 customers in month 3, you cannot divide month-3 S&M spend by 10. Use a rolling 3-month (or full S&M cycle) average.
Error 4: Blended CAC hiding channel problems
If paid CAC is $5,000 but organic CAC is $200, the blended CAC ($2,600) hides the fact that paid is unprofitable. Segment by channel.
CAC Payback Period (Related Metric)
CAC Payback = CAC ÷ (ARPU × Gross Margin%)
At CAC $2,000 and ARPU $150 × 75% margin = $112.50/month:
Payback = $2,000 ÷ $112.50 = 17.8 months
CAC payback benchmarks:
| CAC Payback | Assessment |
|---|---|
| < 12 months | Excellent — efficient growth |
| 12-18 months | Good — standard for most SaaS |
| 18-24 months | Monitor closely |
| > 24 months | Fix before scaling spend |
CAC payback above 24 months is a cash flow problem at scale — you pay to acquire customers 2+ years before recovering the cost.
How to Improve Your LTV:CAC
Improve LTV:
- Reduce churn (highest impact — churn denominator in LTV formula)
- Increase ARPU through expansion/upsell
- Improve gross margins (reduce infrastructure, support costs)
Reduce CAC:
- Shift mix to lower-CAC channels (organic, referral, product-led)
- Improve conversion rates at each funnel stage
- Reduce sales cycle length
- Add self-serve/product-led buying option
The fastest wins:
A 25% churn reduction (2% → 1.5% monthly) increases LTV by 33% with no other changes.
A 20% conversion rate improvement on website reduces paid CAC by 20%.
Together, these changes can move a 2.5:1 ratio to 4:1+ without new product development.
Use the Customer LTV Calculator to model your LTV:CAC ratio and simulate the impact of different improvements.