LTV vs CAC — a step-by-step guide to startup unit economics
LTV vs CAC — a step-by-step guide to startup unit economics
LTV:CAC is probably the most quoted and most often miscalculated metric in SaaS. I've seen startups report LTV:CAC = 8 on a pitch deck and fail to explain how they got there.
Let's break it down step by step, the right way.
1. LTV (Lifetime Value) — what it is and how to calculate it
LTV is how much revenue a customer brings over their entire lifetime as a customer.
Simple formula for B2C / e-commerce:
LTV = AOV × purchases per year × customer lifetime (years)
Example:
- AOV = $250
- 4 purchases per year
- Lifetime = 3 years
LTV = 250 × 4 × 3 = $3,000
Formula for B2B SaaS:
LTV = ARPA / Monthly Churn Rate
Where ARPA = Average Revenue Per Account (=MRR per customer). Example:
- ARPA = $200/mo
- Monthly Churn = 2%
LTV = 200 / 0.02 = $10,000
Pitfall 1: don't confuse Customer Churn and Revenue Churn. If your Customer Churn = 5% but Revenue Churn = 2% (small customers leave, big ones stay and upsell), use Revenue Churn for LTV.
Pitfall 2: if you have a short history (<24 months), LTV is a prediction, not a fact. Stay humble: multiply your projected LTV by 0.7-0.8 for a conservative estimate.
2. CAC (Customer Acquisition Cost) — what to include
CAC = (Marketing + Sales spend) / number of new paying customers in the period.
In Marketing + Sales, include everything:
- Ads (Facebook, Google Ads, LinkedIn)
- Salaries of the sales and marketing teams
- Tools (CRM, marketing automation, attribution)
- Contractor fees, consultants
- Content, design, video production
Pitfall: Blended CAC vs Paid CAC.
| Type | What it includes | When to show it | ||
|---|---|---|---|---|
| Blended CAC | All spend / all new customers (including organic) | Investor pitch (looks better) | ||
| Paid CAC | Paid channels only / paid customers only | Operational decisions (the real picture) |
3. LTV:CAC — what ratio is healthy
| LTV:CAC | What it means | ||
|---|---|---|---|
| <1 | Every new customer is a loss. The business model is broken | ||
| 1-3 | Below par. Only acceptable if growth is the priority over unit economics (early stage) | ||
| ≥3 | Healthy SaaS unit economics | ||
| >5 | Great, but you may be under-investing in marketing — competitors will take the market | ||
| >8-10 | You're definitely under-investing. Hire sales/marketing now |
Why 3, not 2 or 4? Because:
- 1× — break-even (on paper, ignoring COGS, support, churn)
- 2× — break-even after real costs
- 3× — buffer for unpredictable churn / margin compression
- ≥3 = sustainable growth
4. CAC Payback Period — why LTV:CAC isn't enough
LTV:CAC = 5 sounds great. But if payback = 36 months, you'll hit a cash crunch before the customer ever pays back.
CAC Payback = CAC / (MRR per customer × Gross Margin)
Benchmarks:
- B2B SaaS SMB: <12 months
- B2B SaaS Mid-market: 12-18 months
- B2B SaaS Enterprise: 18-24 months
- B2C: usually <6 months
Real-world example:
- LTV = $10,000
- CAC = $2,000 → LTV:CAC = 5× ✓
- MRR per customer = $200
- Gross Margin = 80%
Payback = 2000 / (200 × 0.80) = 2000 / 160 = 12.5 months
Healthy SaaS. If payback >24 months — even with LTV:CAC = 5, cash flow is problematic.
5. Goal mode — the reverse calculation
A frequently useful question: "With a target LTV:CAC = 3 and my LTV of $5,000, what's the maximum CAC I can afford?"
Answer: $5,000 / 3 = $1,667
If your actual CAC is higher, you need to either lower it or raise LTV.
The calculator below can run this in reverse — set a target LTV:CAC and it shows the required CAC at your LTV.
6. How to improve LTV:CAC
Lower CAC
1. Organic channels — SEO, content, sharing, referrals. This lowers blended CAC at scale 2. Referral programs — referral CAC is usually 30-50% of paid CAC 3. Conversion optimization — every +10% to funnel CR = -10% to CAC 4. Brand awareness — a brand lowers CPC and CPM on paid 5. Self-serve onboarding for SMB — removes sales costRaise LTV
1. Reduce churn — onboarding, customer success, health scoring 2. Raise AOV / ARPA — upsells, bundles, premium tiers 3. Increase frequency — email flows, retention campaigns 4. Long contracts — annual prepay cuts churn ×12 5. Expansion revenue — NRR-driven (see the separate post)7. When LTV:CAC is MISLEADING
- Too short a history — LTV is calculated on 12 months of data, but customers may churn after 18
- Margin not included — gross LTV vs net LTV (after COGS)
- Discount rate — a future $1 is worth less than today's; for long-tail LTV apply NPV
- Cohort skew — one large customer distorts the all-customers average
Real-world: common mistakes
Mistake 1: "We have LTV:CAC = 8"
→ Ask: blended or paid? Paid is usually much lower.
Mistake 2: "We're growing exponentially, LTV:CAC doesn't matter"
→ It does. Without a healthy LTV:CAC, growth = accelerating toward bankruptcy. (RIP Casper, MoviePass.)
Mistake 3: "LTV:CAC = 12 — awesome!"
→ Most likely CAC is understated (sales team not included), or LTV is miscalculated (churn not accounted for).
Bottom line
LTV:CAC is a simple but critical metric. Calculate both: gross + paid CAC. Triangulate with CAC Payback Period. If LTV:CAC ≥3 AND payback <18 months → you have healthy SaaS unit economics and can scale.
Calculate your LTV:CAC below — the built-in calculator shows the ratio, the benchmark and the reverse calculation (target LTV:CAC → required CAC).
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Further resources
- /en/ltv — LTV calculator on its own
- /en/cac — CAC calculator on its own
- /en/cacPayback — CAC Payback Period
- David Skok's original post on LTV:CAC
- /en/burnMultiple — Burn Multiple, the macro capital-efficiency metric