What this number actually tells you
The simple churn-based LTV formula is most useful as a transparent directional model. It assumes customer churn, average revenue per account, and gross margin remain stable over the estimated lifetime.
Match acquisition spend and new customers from the same period, channel, and segment. Compare the result with historical cohorts before using it for budget or pricing decisions.
Use the formula you can reproduce next month
Customer acquisition cost
CAC = Sales and marketing acquisition spend / New paying customers
CAC assigns the acquisition spend from one period, channel, or segment to the paying customers acquired from that same scope.
- Acquisition spend: Fully loaded sales and marketing cost used to acquire the selected customers, including the cost categories defined by your reporting policy.
- New paying customers: Customers whose first paid subscription is attributed to the same period, channel, and segment as the acquisition spend.
Unadjusted revenue lifetime value
Revenue LTV = Monthly ARPA / Monthly customer churn
Revenue LTV estimates lifetime recurring revenue before the cost of delivering the service. Keep it secondary to the gross-margin-adjusted value when comparing LTV with acquisition cost.
Gross-margin-adjusted customer lifetime value
LTV = (Monthly ARPA x Gross margin) / Monthly customer churn
This simplified SaaS LTV estimate divides monthly gross profit per account by monthly logo churn. Enter gross margin and churn as decimals inside the formula.
- Monthly average revenue per account: Average monthly recurring revenue for one paying customer account in the selected population.
- Gross margin: The share of revenue remaining after cost of revenue, expressed as a percentage and applied consistently to the selected population.
- Monthly customer churn rate: The percentage of starting customer accounts lost in one month. This is logo churn, not revenue churn.
Estimated customer lifetime
Estimated lifetime in months = 1 / Monthly customer churn
This inverse-churn heuristic assumes a stable monthly churn probability and a steady-state customer population.
LTV:CAC ratio
LTV:CAC = Gross-margin-adjusted LTV / CAC
The ratio compares modeled gross-profit value with the fully loaded cost to acquire a customer from the same population.
CAC payback period
CAC payback months = CAC / (Monthly ARPA x Gross margin)
Payback estimates how many months of average gross profit are needed to recover acquisition cost before churn, expansion, discounting, or payment timing changes the model.
SaaS LTV:CAC worked example
A SaaS company measures one customer segment with $500 monthly average revenue per account, 80 percent gross margin, and 2 percent monthly customer churn.
- Monthly ARPA: $500
- Gross margin: 80%
- Monthly customer churn: 2%
- Sales and marketing acquisition spend: $120,000
- New paying customers: 40
CAC = $120,000 / 40 = $3,000
Monthly gross profit per account = $500 x 0.80 = $400
Estimated lifetime = 1 / 0.02 = 50 months
Revenue LTV = $500 / 0.02 = $25,000
LTV = $400 / 0.02 = $20,000
LTV:CAC = $20,000 / $3,000 = 6.67
CAC payback = $3,000 / $400 = 7.5 months
Under the model assumptions, each acquired customer has an estimated $25,000 revenue LTV and $20,000 gross-margin-adjusted LTV, costs $3,000 to acquire, and repays that acquisition cost after 7.5 months of average gross profit.
Keep the measurement boundary clean
Keep every input aligned to the same customer segment and acquisition scope. Document the cost categories used in CAC.
Include
- Recurring revenue per paying customer account, normalized to one month.
- Gross margin after the cost of delivering the service under your documented finance policy.
- Monthly logo churn for the same customer segment used for average revenue per account.
- Fully loaded acquisition costs such as relevant sales and marketing payroll, commissions, programs, advertising, agencies, data, and tools under one consistent policy.
- New paying customers attributed to the same period, channel, and segment as the acquisition spend.
Exclude
- Leads, trials, free accounts, and opportunities that did not become paying customers.
- Revenue churn substituted for customer churn in the inverse-churn lifetime formula.
- Expansion, reactivation, and future price changes unless you use a separate model that explicitly supports them.
- Spend or customers from mismatched periods, channels, products, currencies, or segments.
Read the result before you react to it
Treat the outputs as connected assumptions, not as independent grades. A change in churn, margin, revenue, spend, or customer count moves several results at once.
LTV:CAC changes between periods
At least one modeled input changed: customer value, gross margin, churn, acquisition spend, or acquired-customer count.
Next checkBridge the change by input and segment before increasing or cutting acquisition investment.
CAC payback lengthens
Acquisition cost rose, monthly gross profit per account fell, or both occurred in the selected population.
Next checkSeparate pricing, margin, channel cost, conversion, and customer-mix effects, then compare payback with actual cohort cash collection.
Modeled LTV rises because churn falls
The inverse-churn assumption projects a longer average lifetime while monthly gross profit stays constant.
Next checkConfirm the change across mature cohorts and enough observation time before treating the modeled gain as durable.
Blended economics look stable but segments diverge
Strong economics in one channel, plan, or customer group may be offsetting weaker economics elsewhere.
Next checkRecalculate using matched segment-level ARPA, margin, churn, spend, and customer counts.
What the simple model cannot settle
Inverse-churn LTV assumes a stable churn probability. Real churn often changes with tenure, contract term, onboarding cohort, plan, and customer segment.
The simple formula does not model expansion, contraction, reactivation, discount rates, payment timing, or changes in average revenue and margin.
A zero monthly churn input cannot produce a finite churn-based lifetime value. Use observed cohort economics or a bounded planning horizon instead.
A zero CAC does not produce a meaningful LTV:CAC ratio, and zero monthly gross profit does not produce a finite CAC payback period. Report those states explicitly instead of substituting an arbitrary number.
Blended company-wide averages can hide channels or customer segments with very different acquisition cost and lifetime value.
CAC payback uses average gross profit and does not replace a cash-flow model, cohort contribution analysis, or accounting review.
Questions that change the calculation
How do you calculate SaaS LTV?
A common simple formula divides monthly gross profit per account by monthly customer churn. Monthly gross profit per account equals monthly average revenue per account multiplied by gross margin. This model assumes revenue, margin, and churn remain stable, so validate it against historical customer cohorts.
How do you calculate customer acquisition cost?
Divide fully loaded sales and marketing acquisition spend by new paying customers acquired from the same period, channel, and segment. Document which payroll, commissions, media, agency, data, and tool costs are included so CAC remains comparable.
Why does this LTV calculator use gross margin?
Revenue is not the same as economic value. Applying gross margin estimates the gross profit available after the cost of delivering the service, which makes LTV and CAC payback more comparable to acquisition cost.
What if monthly customer churn is zero?
The inverse-churn formula would divide by zero and cannot produce a finite estimate. Use a longer observation window, a mature cohort, or a bounded lifetime assumption instead of treating LTV as infinite.
What is the difference between LTV:CAC and CAC payback?
LTV:CAC compares total modeled lifetime gross profit with acquisition cost. CAC payback estimates the months of average gross profit needed to recover acquisition cost. One is a lifetime value relationship and the other is a recovery-time estimate.
Unit economics improve one customer decision at a time.
LTV:CAC can expose pressure from churn, margin, ARPA, or acquisition cost. It cannot identify the accounts, behaviors, or handoffs creating that pressure. Prevenue helps teams connect those signals to a reviewable next action without replacing finance or cohort reporting.
See how the Prevenue Revenue Signals Platform turns account evidence into governed next actions while humans keep control.