Every investor pitch deck has a slide called “Unit Economics.” Most of them are wrong. Not intentionally — founders just calculate these numbers differently than investors expect, and the gap creates distrust at exactly the moment you need credibility.
I'm going to walk through the five unit economics metrics that matter most for SaaS companies, using a real example: a $100/month B2B product. No hand-waving. Actual math.
Metric 1: Customer Acquisition Cost (CAC)
CAC is the total cost to acquire one new customer. The formula is simple. The execution is where founders go wrong.
Formula: Total sales and marketing spend / Number of new customers acquired (in the same period)
Here's where it gets tricky. “Total sales and marketing spend” means everything:
- Ad spend (Meta, Google, LinkedIn)
- Sales team salaries and commissions
- Marketing team salaries
- Marketing software (HubSpot, Mailchimp, etc.)
- Content creation costs
- Event sponsorships
- Agency fees
Most founders only include ad spend. That's not CAC — that's paid acquisition cost. Your investor will calculate the fully loaded number, and if it's 3x what you showed on your slide, you've lost credibility.
Example: You spend $45K/month on sales and marketing (all-in, including two salespeople and a marketing manager). You acquire 30 new customers per month.
CAC = $45,000 / 30 = $1,500
For a $100/month product ($1,200 ACV), that's a CAC of $1,500. We'll come back to whether that's good or bad.
Metric 2: Customer Lifetime Value (LTV)
LTV is the total revenue you expect from a customer over their entire relationship with you. The standard formula uses churn rate:
Formula: ARPU / Monthly churn rate
Or equivalently: ARPU x Average customer lifetime (in months)
Example: Your product is $100/month. Your monthly churn rate is 3% (meaning 3% of customers cancel each month).
LTV = $100 / 0.03 = $3,333
Average customer lifetime = 1 / 0.03 = 33.3 months (about 2.8 years)
That means each customer, on average, will pay you $3,333 before they cancel.
The gross margin adjustment. Sophisticated investors will ask for gross-margin-adjusted LTV. If your gross margin is 80% (you spend $20/month per customer on hosting, support, etc.), then:
Gross-margin-adjusted LTV = $3,333 x 0.80 = $2,667
This is the number that matters, because it represents the actual profit contribution of a customer, not just revenue.
Metric 3: LTV:CAC Ratio
This is the ratio investors obsess over. It answers: “For every dollar you spend acquiring a customer, how many dollars do you get back?”
Formula: LTV / CAC
Example: LTV = $3,333. CAC = $1,500.
LTV:CAC = $3,333 / $1,500 = 2.2x
Using gross-margin-adjusted LTV: $2,667 / $1,500 = 1.8x
What investors want to see:
- Below 1.0x: You're losing money on every customer. This is a burning building.
- 1.0x – 2.0x: You're in the danger zone. Marginal economics that can tip negative with any increase in CAC or churn.
- 3.0x: The benchmark. This is what most VCs consider “healthy” for a growth-stage SaaS company.
- 5.0x+: Either your economics are exceptional or you're under-investing in growth. Investors might push you to spend more on acquisition.
Our example at 1.8x (gross-margin-adjusted) is below the 3.0x benchmark. That means either CAC needs to come down or LTV needs to go up. Let's look at how.
Metric 4: CAC Payback Period
Payback period tells you how many months it takes to recoup the cost of acquiring a customer. Investors care about this because it determines how much capital you need to grow.
Formula: CAC / (ARPU x Gross Margin)
Example: CAC = $1,500. ARPU = $100/month. Gross margin = 80%.
Payback period = $1,500 / ($100 x 0.80) = $1,500 / $80 = 18.75 months
That means it takes almost 19 months before a customer becomes profitable. For a SaaS company with 33-month average customer lifetime, that's tight. Only 14 months of “profit” per customer.
What investors want to see:
- Under 12 months: Great. You recover your acquisition cost within a year.
- 12–18 months: Acceptable for enterprise SaaS with long contracts and low churn.
- 18+ months: Red flag. You need a lot of capital to fund growth, and you're exposed to churn risk during the payback window.
Metric 5: Expansion Revenue — The Game Changer
Here's where the math gets interesting. Everything above assumes flat revenue per customer. But the best SaaS companies grow revenue within their existing customer base through upsells, cross-sells, and usage-based pricing.
This is measured as net revenue retention (NRR). If your NRR is 110%, it means that for every $100 in MRR you had a year ago, you now have $110 from the same cohort — even after accounting for churn and contraction.
Impact on LTV: With expansion revenue, LTV changes dramatically. Instead of using simple churn-based LTV, you use:
LTV = ARPU / (Churn rate - Net expansion rate)
Example: Monthly churn = 3%. Monthly expansion rate from upsells = 1.5%. Net churn = 1.5%.
Adjusted LTV = $100 / 0.015 = $6,667
That doubles the LTV from $3,333 to $6,667. And it changes the LTV:CAC ratio from 2.2x to 4.4x. Suddenly the same business looks fundable.
This is why investors ask about expansion revenue early in due diligence. A SaaS company with 3% gross churn and 1.5% expansion looks very different from one with 3% gross churn and no expansion — even though the product, team, and market might be identical.
Putting It All Together: The $100/Month Product
Here's our complete unit economics profile:
- ARPU: $100/month ($1,200 ACV)
- Monthly churn: 3%
- Monthly expansion: 1.5%
- Gross margin: 80%
- Fully loaded CAC: $1,500
- LTV (simple): $3,333
- LTV (with expansion): $6,667
- LTV:CAC (simple, GM-adjusted): 1.8x
- LTV:CAC (with expansion, GM-adjusted): 3.6x
- Payback period: 18.75 months
The story this tells: the business works, but it's dependent on expansion revenue. Without upsells, unit economics are marginal. With upsells, they're strong. An investor will look at this and ask: “How reliable is your expansion motion? Is it built into the product (usage-based pricing) or does it require a sales team (seat-based upgrades)?”
How to Improve Your Numbers
Reduce CAC: Invest in organic channels (content, SEO, community). Build a referral program. Improve your sales team's close rate. Every 10% reduction in CAC directly improves LTV:CAC ratio by 10%.
Reduce churn: This has the biggest impact on LTV. Cutting monthly churn from 3% to 2% increases simple LTV from $3,333 to $5,000 — a 50% improvement from a single percentage point. Track churn by cohort and by segment to find the specific leaks.
Increase expansion: Build pricing tiers that grow with customer usage. Introduce add-on products. Implement annual contracts with built-in price escalators. Model the impact before you build.
Raise prices: If your LTV:CAC ratio is strong (above 4x), you might be underpriced. Test a 20% price increase with new customers and measure the impact on conversion rate. Most SaaS companies can absorb a 20% price increase with less than a 5% drop in conversion.
The Bottom Line
Unit economics aren't a slide you build for investors. They're the operating system of your business. Every decision — how much to spend on marketing, when to hire salespeople, whether to build a new feature or improve retention — should be filtered through unit economics.
If you don't know your real CAC, your real churn rate, or your real LTV, you're making these decisions on instinct. Sometimes instinct is right. But at $100K/month in burn, you don't want to bet on “sometimes.”
