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Business Fundamentals
Unit Economics: CAC, LTV, and Why They Matter
If it costs more to acquire a customer than they're worth, you don't have a business. Here's how to understand and optimize unit economics.
Unit economics answer a simple question: Do you make money on each customer?
If it costs $500 to acquire a customer who generates $1,000 in revenue, you have a business. If it costs $500 to acquire a customer who generates $200, you don’t—you’re just turning VC dollars into growth that can’t sustain itself.
The Core Metrics
CAC (Customer Acquisition Cost)
How much it costs to acquire a customer.
Formula:
CAC = Total Sales & Marketing Spend / Number of New Customers
Example:
•
Marketing spend: $50,000
•
Sales salaries: $30,000
•
New customers: 100
•
CAC = $80,000 / 100 = $800
What to include:
•
Advertising spend
•
Marketing salaries
•
Sales salaries and commissions
•
Marketing tools and software
•
Content production costs
What not to include:
•
Product development
•
Customer success (post-sale)
•
General overhead
LTV (Lifetime Value)
How much revenue a customer generates over their entire relationship.
Simple formula:
LTV = ARPU × Average Customer Lifetime
Where:
•
ARPU = Average Revenue Per User (monthly or annual)
•
Average Customer Lifetime = 1 / Churn Rate
Example:
•
ARPU: $100/month
•
Monthly churn: 5%
•
Average lifetime: 1 / 0.05 = 20 months
•
LTV = $100 × 20 = $2,000
More precise formula (accounting for gross margin):
LTV = (ARPU × Gross Margin) / Churn Rate
LTV:CAC Ratio
The relationship between what customers are worth and what they cost.
Formula:
LTV:CAC Ratio = LTV / CAC
Benchmarks:
•
1:1 = Break even (bad—no profit)
•
3:1 = Healthy
•
5:1+ = Very efficient (or underinvesting in growth)
Example:
•
LTV: $2,000
•
CAC: $800
•
Ratio: 2,000 / 800 = 2.5:1
At 2.5:1, you’re making money but could be more efficient.
Payback Period
How long until you recover CAC.
Formula:
Payback Period = CAC / (ARPU × Gross Margin)
Example:
•
CAC: $800
•
Monthly ARPU: $100
•
Gross margin: 80%
•
Payback = $800 / ($100 × 0.80) = 10 months
Benchmarks:
•
Under 12 months: Good
•
12-18 months: Acceptable
•
Over 18 months: Concerning (for most businesses)
Shorter payback means faster reinvestment of capital.
Why Unit Economics Matter
Sustainability
Businesses with bad unit economics can grow by burning cash, but they can’t survive without continuous funding. Good unit economics mean you can sustain growth independently.
Scalability
If every customer loses money, scaling makes things worse. Unit economics tell you whether growth is actually desirable.
Fundraising
Investors scrutinize unit economics. Bad ratios signal the business might never be profitable.
Decision Making
Unit economics inform:
•
How much to spend on acquisition
•
Which channels to invest in
•
How to price
•
Where to focus retention efforts
Breaking Down CAC by Channel
Not all channels have the same CAC:
Channel
Spend
Customers
CAC
Paid ads
$30,000
30
$1,000
Content marketing
$10,000
40
$250
Referrals
$5,000
20
$250
Outbound sales
$25,000
10
$2,500
Knowing CAC by channel helps you allocate budget wisely.
Breaking Down LTV by Segment
Not all customers are equally valuable:
Segment
ARPU
Churn
LTV
Enterprise
$500
2%
$25,000
Mid-market
$200
5%
$4,000
SMB
$50
10%
$500
You might accept higher CAC for enterprise customers given their higher LTV.
Improving Unit Economics
Reduce CAC
Improve conversion rates:
•
Better landing pages
•
Smoother onboarding
•
Clearer messaging
Find efficient channels:
•
Double down on low-CAC channels
•
Reduce spend on high-CAC channels
•
Invest in organic (SEO, content, referrals)
Shorten sales cycles:
•
Self-serve where possible
•
Better qualification
•
Reduce friction
Increase LTV
Reduce churn:
•
Better onboarding
•
Proactive customer success
•
Product improvements
Increase ARPU:
•
Raise prices
•
Upsell and cross-sell
•
Usage-based expansion
Extend lifetime:
•
Annual contracts
•
Switching costs
•
Continuous value delivery
Improve Gross Margin
Reduce costs to serve:
•
Efficient infrastructure
•
Automation of support
•
Better architecture
Higher gross margin means more of each revenue dollar contributes to LTV.
Common Mistakes
Blended CAC Hiding Problems
Your blended CAC might look fine while one channel is terrible:
•
Blended CAC: $500
•
But: Paid ads CAC: $1,500, Organic CAC: $100
You’re subsidizing bad paid performance with organic. Analyze by channel.
Ignoring Time Value of Money
$1,000 in 36 months is worth less than $1,000 today. Long payback periods tie up capital.
Optimistic Lifetime Assumptions
Don’t assume customers stay forever. Use actual retention data, not hopes.
Excluding Costs from CAC
Marketing attribution is hard, but don’t artificially lower CAC by excluding costs that contribute to acquisition.
Forgetting Gross Margin
Revenue isn’t profit. A $100/month customer with 50% margin contributes $50 to covering CAC.
Unit Economics at Different Stages
Pre-PMF
Unit economics are often bad and that’s okay:
•
You’re learning, not optimizing
•
Low volume makes calculations unreliable
•
Focus on retention and activation first
Post-PMF
Time to care about unit economics:
•
Calculate accurately
•
Identify efficient channels
•
Set targets for improvement
Growth Stage
Unit economics should be good and improving:
•
3:1+ LTV:CAC
•
Under 12 month payback
•
Positive contribution margin
Scale
Optimize aggressively:
•
Channel-level optimization
•
Segment-specific strategies
•
Predictive modeling
Presenting Unit Economics
To investors, present:
1.
LTV calculation with assumptions clear
2.
CAC calculation with what’s included
3.
LTV:CAC ratio and how it compares to benchmarks
4.
Payback period and cash flow implications
5.
Trends over time (improving is better than static)
6.
Segmentation showing best customer profiles
Be honest about limitations in your data.
Key Takeaways
•
CAC = total acquisition cost / new customers
•
LTV = ARPU × average customer lifetime (or ARPU × gross margin / churn)
•
Target 3:1+ LTV:CAC ratio, under 12-month payback
•
Calculate by channel and segment—blended numbers hide problems
•
Improve CAC through conversion, efficient channels, shorter sales cycles
•
Improve LTV through reduced churn, higher ARPU, longer contracts
•
Unit economics matter most after PMF; before that, focus on retention
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