LTV:CAC Ratio: The Unit Economics North Star
The ratio of customer lifetime value to acquisition cost tells you whether your growth engine creates or destroys value.
| Model | Seed | Series A | Series B | Top quartile |
|---|---|---|---|---|
| B2B SaaS | 2-3x | 3-5x | 4-6x | 3x+ |
| Consumer | 1.5-2.5x | 2-4x | 3-5x | 3x+ |
The LTV:CAC ratio compares the total gross profit a customer generates over their lifetime to the cost of acquiring them. It's the definitive measure of whether your business model works — a ratio above 3x means you're creating durable value, while below 1x means you're literally paying customers to use your product.
What It Is
LTV:CAC = Customer Lifetime Value / Customer Acquisition Cost. LTV = ARPU x Gross Margin x Average Customer Lifespan (in months). If your average customer pays $200/month at 75% gross margin and stays for 30 months, LTV = $200 x 0.75 x 30 = $4,500. If CAC is $1,200, your ratio is 3.75x.
Why It Matters
LTV:CAC is the ultimate reality check on growth sustainability. A ratio of 1x means you break even on every customer — growth generates zero profit. At 3x, you have healthy margins to fund operations and reinvest. Above 5x suggests you may be under-investing in growth and leaving market share on the table. The magic zone is 3-5x for most SaaS businesses.
How to Calculate It
The tricky part is estimating lifetime accurately. For early-stage companies without years of retention data, use: LTV = ARPU x Gross Margin / Monthly Churn Rate. This assumes steady-state churn, which overestimates LTV for companies with improving retention and underestimates it for those with worsening churn. Calculate by segment — your enterprise LTV:CAC likely looks very different from SMB.
Startup Anecdote
Casper, the mattress startup, is a cautionary tale of what happens when you ignore LTV:CAC. They spent heavily on digital advertising and brand marketing, driving CAC above $300 for a one-time purchase averaging $800-1,000 with roughly 50% gross margins. With LTV around $400-500 and CAC at $300+, their ratio hovered around 1.3-1.5x — barely viable. The math never worked at scale because mattresses are infrequent purchases with limited expansion potential. Despite $400M+ in revenue, they never achieved profitability and eventually sold at a fraction of their peak valuation.
Key Takeaway
Obsess over LTV:CAC by channel and segment. Some channels will deliver 5x+ ratios while others destroy value at 1x. Kill the underperformers ruthlessly. And remember that LTV:CAC is dynamic — improving retention, expanding ARPU, or reducing CAC through product-led growth can transform your economics without changing your pricing.