Unit Economics 101: How to Calculate CAC, LTV, and Payback Period

Customer Acquisition Cost (CAC)

CAC is the total cost of acquiring one new customer. This includes all sales and marketing expenses in a period divided by the number of new customers acquired in that period. If you spend $50,000 on sales and marketing in a quarter and acquire 10 new customers, your CAC is $5,000. A nuance worth noting: some businesses calculate blended CAC (all customers) and paid CAC (excluding organic) separately, which gives different insights.

CAC is the total cost to acquire a new customer. This includes sales compensation (base and commission), marketing spend (ads, events, content, agency fees), sales tools, and any directly attributable overhead. Divide total acquisition cost by new customers acquired in the period. The answer is CAC.

The definition of "total acquisition cost" is where methodology matters. Some companies include only direct marketing spend. Some include sales team salaries. Some include allocation of marketing ops and systems. The right answer is: include all costs that would not exist if you were not acquiring customers. Investors will want to see CAC calculated this way because it is the true acquisition cost.

Lifetime Value (LTV)

LTV is the total revenue or margin a customer is expected to generate over the entire relationship. For a subscription business, it's typically average monthly revenue divided by monthly churn rate. If a customer pays $2,000 per month and your monthly churn rate is 2%, the LTV is $100,000. For service businesses without subscriptions, LTV is typically calculated from historical data on how long clients stay and what they pay.

LTV is the total revenue or gross profit a customer produces over their lifetime with you. The calculation depends on your business model. For subscription: monthly revenue times gross margin divided by monthly churn rate. For transactional: average revenue per customer times expected number of purchases times gross margin. For services: annual revenue times gross margin times average client tenure.

LTV calculations assume historical retention rates continue. If your churn has been 2% monthly for 3 years, LTV math assumes 2% continues. This is reasonable for stable businesses. For rapidly growing companies where retention data is thin or changing, LTV can be misleading. A better approach: calculate LTV at cohort level and look at trends.

Payback period

Payback period is how long it takes to recover the CAC from a customer's gross margin contribution. If your CAC is $5,000 and a client generates $1,000 of gross profit per month, your payback period is 5 months. Investors generally want to see payback periods under 12-18 months for growth-stage businesses, longer payback periods mean more capital is tied up in customer acquisition before it's recovered.

Payback period is the time for a new customer to pay back their acquisition cost in gross profit. CAC divided by monthly gross profit per customer. A SaaS company with $1,800 CAC and $200 monthly gross profit per customer has a 9-month payback. Anything under 12 months is healthy. 12-18 months is acceptable with strong retention. Past 18 months signals problems.

Payback matters more than LTV for cash management. LTV tells you the theoretical return over years. Payback tells you when the cash outlay starts working for you. A company with excellent LTV but 36-month payback has a cash flow problem that can constrain growth. A company with moderate LTV but 9-month payback can reinvest faster and grow faster.

The LTV:CAC ratio

The LTV:CAC ratio is the shorthand metric that investors use to evaluate business model health. A ratio of 3:1 or higher is generally considered healthy, you're generating 3x the LTV of what it costs to acquire a customer. Below 1:1 means you're losing money on every customer acquired. If you don't know your LTV:CAC ratio, it's worth calculating, it will tell you something important about your business.

LTV:CAC ratio is the headline unit economics number. 3:1 is the benchmark. Above that is healthy. Below 3:1 means you are barely covering acquisition costs over a customer's lifetime. Above 5:1 is exceptional and usually suggests either very high retention, underinvestment in growth, or both.

The trap with LTV:CAC is that it is backward-looking and highly sensitive to assumptions. A small change in assumed lifetime or churn rate can move LTV:CAC from 3:1 to 6:1 or vice versa. Use it as one data point among several, not as the single number that decides acquisition strategy.