Define the customer and the acquisition cost
Customer acquisition cost is acquisition spending divided by acquired customers. That sounds straightforward, but the numerator and denominator need a written policy. Are you counting paid accounts, individual seats, first purchases, or free registrations? A free trial is not automatically a paying customer.
CAC = attributable acquisition spending ÷ newly acquired customers
A fully loaded version may include advertising, agency fees, sales compensation, marketing software, and the relevant portion of staff time. A paid-channel CAC may include only directly attributed media and campaign costs. Both can be useful; they answer different questions and should not share an unlabeled chart.
Match spending to the customers it helped acquire. In a long sales cycle, dividing this month's sales payroll by this month's closed deals can produce a noisy ratio because many deals were developed in earlier months.
Worked example: CAC, contribution LTV, and payback
Assume an illustrative business spends $30,000 to acquire 100 paying accounts. Each account produces $50 of monthly revenue, gross margin is 80%, and monthly customer churn is assumed to remain at 4%.
| Metric | Calculation | Result |
|---|---|---|
| CAC | $30,000 ÷ 100 | $300 |
| Monthly gross profit per account | $50 × 80% | $40 |
| Simplified contribution LTV | $40 ÷ 4% | $1,000 |
| LTV:CAC | $1,000 ÷ $300 | 3.33:1 |
| Simple CAC payback | $300 ÷ $40 | 7.5 months |
This is a simplified steady-state model, not a promise that an account will stay exactly 25 months. It assumes stable revenue, margin, and churn, with no expansion, discounting, or additional retention cost. The payback figure also assumes the account stays active through the payback period.
Revenue LTV and contribution LTV are different
Revenue LTV excludes the cost of serving the customer. Gross-margin-adjusted LTV subtracts the modeled cost of delivering the service but may still exclude support categories, corporate overhead, or taxes depending on accounting policy.
Before comparing two dashboards, confirm the definitions. Stripe's documentation illustrates why this matters: subscription metrics have configurable treatments, including discounts and the point at which a subscriber becomes active. A similar metric name does not guarantee the same underlying calculation. [1]
Never compare a revenue-based LTV with a contribution-based benchmark without adjusting the basis. Write the formula next to the number so another person can reproduce it.
Why the churn shortcut can fail
The simple formula monthly contribution ÷ monthly churn becomes unstable when churn is tiny and is undefined at zero churn. “We have not observed a cancellation yet” is not evidence of infinite customer value.
New businesses often have limited follow-up. Early customers may be unusually committed, while later acquisition channels bring different users. Cancellation risk can also change with tenure, contract renewal, price increases, and product maturity.
Use cohort analysis when possible. Group customers by acquisition month or channel, track the contribution they actually generate, and separate observed value from forecast value. For a discounted model, calculate the expected contribution in each future period, multiply by the probability of retention, discount it, and add the periods together.
A strong ratio can still hide a cash problem
A high LTV:CAC ratio may depend on profits earned years in the future while acquisition spending is due today. Payback and cash availability therefore matter alongside lifetime value.
Segment the analysis by channel, product, geography where relevant, and customer size. A blended ratio can hide an expensive channel behind customers acquired organically. It can also improve simply because the business cut growth spending, not because a new campaign became more effective.
Make the decision with a range
Instead of presenting a single LTV to the cent, show a base case and a worse-retention case. In the example, raising monthly churn from 4% to 8% cuts the simplified contribution LTV from $1,000 to $500 while CAC remains $300.
Decide how much uncertainty the business can fund. There is no universal ratio that proves a campaign should be scaled. Evidence of durable retention, capacity to serve customers, and the ability to finance payback all belong in the decision.
Frequently asked questions
Is a 3:1 LTV:CAC ratio always good?
No. Its meaning depends on whether LTV is revenue or contribution, how mature the cohorts are, how long payback takes, and whether the assumptions hold.
Can LTV be calculated when churn is zero?
The simplified churn-division formula is undefined at zero. Use observed cohort contribution and an explicitly limited forecast horizon instead of reporting infinite value.
Should CAC include staff salaries?
A fully loaded acquisition metric generally includes the relevant staff costs. A media-only metric can be useful too, but label the scope and avoid comparing it with a fully loaded figure.
Sources & calculation notes
Primary references are linked below. Dates, limits, and product terms can change; confirm the applicable details before acting.
Use this guide thoughtfully. Examples illustrate a calculation method, not a guaranteed outcome. The usefulness of any result depends on the definitions, measurements, and assumptions used.