Unit economics is the term for understanding your business at the level of a single customer: what does it cost to acquire them, how much revenue do they generate over time, and how long until that revenue exceeds the acquisition cost.
For a subscription business, these numbers are the backbone of every strategic decision. Hiring plan? Based on unit economics. Marketing budget? Based on unit economics. Series A raise? Investors will build their return model on your unit economics.
The founders who understand their unit economics deeply make better decisions faster. The ones who do not tend to scale the wrong things.
Customer Acquisition Cost (CAC)
CAC is the total cost of acquiring one new paying customer. The formula:
CAC = Total Sales and Marketing Spend / Number of New Customers Acquired
In the period, include all of the following in "total sales and marketing spend":
- Paid advertising (Google, Meta, LinkedIn, etc.)
- Salaries and commissions for salespeople and marketers
- Content production costs
- Event and conference costs
- Tools (CRM subscriptions, email platforms, ad tools)
What not to include: product and development costs, customer support costs, general overhead.
If you spent $20,000 in March on sales and marketing and acquired 40 new customers, your CAC for March is $500.
CAC is most meaningful when tracked separately by acquisition channel. Your Google Ads CAC might be $200. Your content marketing CAC might be $800. Your LinkedIn outbound CAC might be $1,200. Knowing this lets you allocate budget toward the channels with the best economics.
Customer Lifetime Value (LTV)
LTV is the total net revenue you expect to receive from a customer over their entire relationship with you.
A simple LTV formula for SaaS:
LTV = (Average Monthly Revenue per Customer) / Monthly Churn Rate
If the average customer pays $300 per month and your monthly churn rate is 3%, LTV = $300 / 0.03 = $10,000.
To make this more precise, you should subtract the cost of serving the customer (customer support, infrastructure costs attributable to that customer) to arrive at LTV on a gross margin basis. But at early stage, the simple formula is accurate enough to make decisions.
The LTV:CAC Ratio
This is the ratio that most SaaS investors will ask about. The rule of thumb: LTV should be at least 3x CAC.
- LTV:CAC below 1: You are destroying value with every customer acquired. Every new customer makes you poorer.
- LTV:CAC of 1 to 3: You are breaking even or barely profitable per customer. Growth is possible but slow.
- LTV:CAC of 3 to 5: Healthy. You have room to invest in growth and still return capital.
- LTV:CAC above 5: Strong. You may be underinvesting in marketing. There is likely more growth available at acceptable economics.
If your LTV:CAC is below 3, you have two levers: increase LTV (reduce churn or increase average revenue per customer) or decrease CAC (improve conversion rates, find cheaper channels, shorten sales cycles).
Payback Period
The payback period is how long it takes for the revenue from a customer to exceed what you spent to acquire them.
Payback Period (months) = CAC / (Average Monthly Revenue per Customer x Gross Margin)
If your CAC is $600, average monthly revenue is $150, and gross margin is 80%, your payback period is: $600 / ($150 x 0.80) = $600 / $120 = 5 months.
Payback period matters for cash flow. Every customer acquired requires capital to fund until payback. If you have a 24-month payback period, you need significant capital reserves to grow, because you are funding customer acquisition for two years per customer before you recover the cost.
SaaS businesses with payback periods under 12 months are generally considered capital-efficient. Under 6 months is excellent.
Gross Margin
Gross margin is the percentage of revenue that remains after subtracting the direct costs of delivering the service.
Gross Margin = (Revenue - Cost of Goods Sold) / Revenue x 100
For SaaS, cost of goods sold includes: cloud infrastructure, third-party API costs, and salaries for anyone whose work is directly attributable to delivering the service (such as a dedicated customer onboarding manager).
Software SaaS businesses typically have gross margins of 70-85%. If yours is significantly lower, you either have pricing that does not account for delivery costs or you have delivery costs that are too high.
Gross margin below 60% in a SaaS business is a signal that the business has service characteristics (it requires significant human intervention per customer) rather than pure software characteristics. This is not necessarily bad, but it means scaling requires proportional headcount growth, which limits the economics of the business.
Net Revenue Retention (NRR)
NRR measures how much your existing customer base grows or shrinks in revenue without counting new customer acquisition.
NRR = (Starting MRR + Expansion MRR - Churned MRR) / Starting MRR x 100
An NRR above 100% means your existing customers are spending more than they were before, even accounting for churn. This is the single most powerful indicator of a healthy SaaS business: the customer base grows in value on its own.
NRR above 110% is strong. Above 120% is exceptional. SaaS businesses with high NRR can grow revenue without acquiring a single new customer, which makes them very capital-efficient.
Achieving high NRR requires either a usage-based pricing model (customers pay more as they use more) or a product that has natural expansion mechanics (teams add seats, departments expand usage, additional modules are purchased).
Tracking these numbers in practice
At early stage, a spreadsheet works fine. Build a simple monthly tracking document:
- New MRR from new customers
- Expansion MRR from existing customers
- Churned MRR from cancellations
- Total MRR
- Number of active customers
- Monthly churn rate
- CAC by channel (where available)
Review it monthly with your team. The conversations it generates are more valuable than the numbers themselves.
As you scale, you will want automated reporting that pulls from your payment processor and CRM. Our data analytics team can build this infrastructure so you have real-time unit economic reporting rather than a spreadsheet you update manually.
If you are building a SaaS product and want to make sure the architecture supports the data collection you will need for unit economic analysis from day one, talk to our development team. Retrofitting instrumentation onto an existing product is significantly harder than building with measurement in mind from the start.