Why LTV:CAC Is the North Star Metric
Every VC will ask you for your LTV:CAC ratio. But more importantly, it tells you whether your business model actually works at scale. A company spending $500 to acquire a customer worth $400 is burning cash with every new signup. A company spending $500 to acquire a customer worth $2,000 should be pouring fuel on the fire. These two scenarios look identical on a revenue chart — they diverge completely on unit economics.
Calculate Your CAC
Customer Acquisition Cost is the total cost to acquire one new paying customer. The formula sounds simple, but most founders calculate it wrong by leaving things out.
The CAC Formula
Use the same time period for both numbers — typically a quarter or trailing 12 months. For early-stage companies, use at least 3 months to smooth out variance.
Include in CAC
- +Paid ads (Google, Meta, LinkedIn)
- +Sales team salaries + commissions
- +Marketing team salaries
- +Events and sponsorships
- +Sales tools (CRM, outbound software)
- +Content production costs
Exclude from CAC
- −Customer success / onboarding costs
- −Account management (post-sale)
- −Product development
- −General & administrative costs
- −Support costs (these factor into LTV)
Example
Q1: You spent $120,000 on sales and marketing (including salaries) and acquired 80 new customers. CAC = $120,000 ÷ 80 = $1,500 per customer.
Calculate Your Gross Margin
LTV isn't about revenue — it's about the profit you actually keep. You need gross margin to convert ARPU into something meaningful. For SaaS, gross margin is typically 70-85%. For marketplaces or services businesses, it can be much lower.
Gross Margin Formula
COGS for SaaS = hosting, infrastructure, third-party API costs, and customer support costs directly tied to delivering the product. Do not include sales, marketing, or R&D in COGS.
| Business Type | Typical Gross Margin | Notes |
|---|---|---|
| Pure SaaS | 75–85% | Software-only, low infrastructure cost |
| SaaS + Services | 55–70% | Implementation and onboarding services |
| Marketplace | 50–70% | Depends on take rate and support costs |
| AI-Heavy SaaS | 50–70% | High GPU/API costs drag margin down |
| eCommerce / Physical | 20–45% | COGS includes product manufacturing |
Calculate Your Churn Rate
Churn is the biggest lever in your LTV calculation. Small differences in churn create enormous differences in LTV. A company at 2% monthly churn has an average customer lifetime of 50 months. At 5% churn, it drops to 20 months. That's not a rounding error — it changes whether your business is fundable.
Monthly Churn Rate Formula
Use logo churn (number of customers) for this calculation. Revenue churn (MRR lost ÷ MRR) is useful for expansion tracking but creates a different metric.
Example
You started the month with 400 customers. 12 canceled. Monthly churn = 12 ÷ 400 = 3% monthly. Average customer lifetime = 1 ÷ 3% = 33 months.
Calculate Your LTV
Now you have everything you need. There are two common LTV formulas — a simple version and a gross-margin-adjusted version. Always use the gross-margin-adjusted version. Revenue LTV overstates the business value and leads to bad decisions.
Simple LTV (less accurate)
Use this as a sanity check, not for investor conversations.
Gross Margin LTV (use this one)
This is the profit you actually keep from a customer over their lifetime. This is what investors are looking at.
Worked Example
Evaluate Your LTV:CAC Ratio
Now divide LTV by CAC. This ratio is the single most important signal about whether your go-to-market is working. Too low means you're destroying value with every acquisition. Too high means you're under-investing in growth and leaving market share on the table.
| LTV:CAC Ratio | Signal | What to Do |
|---|---|---|
| < 1x | Destroying value | Stop spending — fix product, pricing, or churn first |
| 1x – 3x | Marginal | Scale cautiously; improve margins or reduce CAC |
| 3x – 5x | Healthy — invest | This is the VC sweet spot — step on the gas |
| > 5x | Under-investing | You could grow faster — increase marketing spend |
Continuing our example
LTV = $6,000. CAC = $1,500. LTV:CAC = 4x. That's healthy. This company should be investing aggressively in sales and marketing.
Calculate CAC Payback Period
LTV:CAC tells you the lifetime return. CAC Payback Period tells you when you get your money back — which matters enormously for cash flow. A 3x LTV:CAC ratio looks great, but if your payback period is 36 months, you need serious capital to grow. Investors want to see payback periods under 18 months.
CAC Payback Period Formula
This gives you the number of months to recoup your acquisition cost on a gross profit basis. Lower is better.
Payback Period Benchmarks
Continuing our example
CAC = $1,500. ARPU × Gross Margin = $200 × 75% = $150/month. Payback = $1,500 ÷ $150 = 10 months. Excellent.
The Single Most Important Takeaway
LTV:CAC only matters if your churn is real. The most common mistake I see is founders who calculate LTV with their best cohort's churn rate, not their average. Use actual trailing churn from your full customer base, not the cohort that survived. Optimistic churn assumptions will make your LTV look 2-3x better than it actually is — and that leads to disastrously wrong hiring and spend decisions. Build your model on reality, not hope.
Tools to Track LTV and CAC
Manually calculating these metrics in a spreadsheet works early on, but as you grow you need a system that tracks them automatically across cohorts, channels, and plans.
Value Add VC Dashboards
Free interactive tools to model and visualize your SaaS unit economics.
- SaaS Metrics Dashboard — full unit economics tracker
- Startup Financial Model — model LTV by plan and cohort
- How to Track Startup KPIs — broader metrics framework
Recommended Software
These tools calculate LTV, CAC, and payback period automatically from your billing data.
- Stripe — built-in MRR, churn, and LTV reporting in dashboard
- ChartMogul — best-in-class SaaS metrics analytics
- Baremetrics — LTV and CAC by cohort, real-time
- ProfitWell — free plan includes LTV analytics
6 Common LTV/CAC Mistakes That Kill Startups
Using revenue LTV instead of gross margin LTV
Revenue LTV ignores that you have costs. A customer generating $10,000 over their lifetime at 30% gross margin is worth $3,000 — not $10,000. Make sure you're calculating profit, not revenue.
Excluding people costs from CAC
The most common cheat. If your sales rep costs $150k/year and closes 50 customers, that's $3,000 per customer just in salary — before ads, tools, or commissions. Always include fully-loaded headcount.
Using a single blended churn rate
SMB and enterprise customers have wildly different churn rates. Your $50/month SMB plan might churn at 6% monthly while your $5,000/month enterprise plan churns at 0.5%. Blending them gives you a meaningless number. Segment by plan.
Ignoring channel-level CAC
Blended CAC across all channels hides what's actually working. Your organic SEO channel might have a $200 CAC while paid LinkedIn ads are running at $4,000. You can't optimize what you're not segmenting.
Not tracking cohort LTV over time
Calculating LTV from a steady-state formula is a projection. Track actual cohort retention curves to see if customers are churning faster or slower than your model predicts. Cohort analysis is the ground truth.
Waiting until Series A to start measuring
The founders who understand unit economics from day one make better product, pricing, and hiring decisions at every stage. Even with 20 customers, start tracking. You'll make different — and better — decisions with this data.