A customer acquisition cost and lifetime value calculator helps you compare what it costs to win a customer with the revenue and contribution profit that customer may generate. This guide explains the CAC formula, several LTV methods, the LTV to CAC ratio, and CAC payback period, with worked examples for ecommerce, SaaS, and service businesses.
Overview
Customer acquisition cost, or CAC, measures the average sales and marketing cost required to acquire one new customer. Lifetime value, or LTV, estimates the value a customer creates over the relationship. Used together, these metrics support decisions about budgets, pricing, retention, and growth targets.
The basic formulas are:
- CAC = total acquisition costs ÷ new customers acquired
- LTV to CAC ratio = LTV ÷ CAC
- CAC payback period = CAC ÷ monthly contribution profit per customer
For meaningful comparisons, keep the numerator and denominator consistent. If CAC includes paid advertising, sales salaries, commissions, creative production, and marketing software, do not compare it with an LTV based only on invoiced revenue. A more decision-ready LTV uses contribution profit: revenue less variable costs such as payment processing, fulfillment, hosting, support, commissions, and other costs that rise with customer activity.
LTV and CAC are not universal scores. They are estimates built from a defined period, customer segment, channel, and set of assumptions. A blended company-wide ratio can hide the fact that one campaign is profitable while another requires too much time to recover its acquisition cost.
How to estimate CAC, LTV, and payback
1. Calculate customer acquisition cost
Choose a measurement period, such as a month or quarter. Add the acquisition costs assigned to the same period, then divide by the number of new customers acquired during that period.
CAC = (advertising + sales costs + campaign tools + relevant creative costs) ÷ new customers
Decide in advance whether the calculation includes brand marketing, sales payroll, discounts used to acquire customers, agency fees, or onboarding labor. There is no single correct boundary for every business, but changing the boundary from one report to the next makes the metric difficult to interpret.
2. Estimate LTV for a one-time purchase business
For a business where customers may purchase repeatedly, a practical estimate is:
LTV = average order value × purchase frequency × expected customer lifespan × contribution margin
For a single-purchase model with limited repeat behavior, use the expected contribution profit from the first order or a measured repeat-purchase estimate. Avoid assuming that every customer will purchase indefinitely. Use observed repeat rates where available and label forecasts as assumptions.
3. Estimate LTV for subscriptions
A simple subscription estimate is:
LTV = average monthly revenue per customer × expected months retained × contribution margin
If monthly churn is stable and expressed as a decimal, a common planning approximation for expected customer lifetime is 1 ÷ monthly churn. For example, a 5% monthly churn assumption is represented as 0.05, producing an estimated lifetime of 20 months. This is a model, not a guarantee. It becomes less reliable when churn changes by customer age, plan, channel, or cohort.
4. Calculate the LTV to CAC ratio
Divide LTV by CAC after deciding whether LTV is based on revenue or contribution profit. A ratio based on contribution profit is generally more useful for testing whether acquisition can support variable delivery costs.
LTV to CAC ratio = contribution-based LTV ÷ fully defined CAC
A ratio above 1 means the estimated contribution value exceeds acquisition cost, but it does not automatically prove that the business is healthy. The result may exclude fixed overhead, refunds, taxes, working-capital needs, or the cost of serving customers before revenue is collected.
5. Calculate CAC payback period
Payback shows how long it takes to recover acquisition cost from contribution profit. For a subscription customer:
Payback in months = CAC ÷ monthly revenue per customer × contribution margin
If a customer produces uneven payments, use a month-by-month cash contribution schedule rather than a simple average. Payback is especially useful when comparing channels with similar LTV but different cash recovery patterns.
Inputs and assumptions
A reusable unit economics spreadsheet should separate reported results from assumptions. Use one row per campaign, channel, product, or customer cohort and include these fields:
| Input | What to record | Why it matters |
|---|---|---|
| Period | Month, quarter, or cohort start date | Defines the comparison window |
| Marketing spend | Ad spend, content, tools, and campaign costs | Builds a consistent CAC numerator |
| Sales cost | Commissions, allocated payroll, and selling costs | Prevents undercounting acquisition effort |
| New customers | Customers attributed to the same period or channel | Provides the CAC denominator |
| Revenue | Collected or recognized revenue, defined consistently | Supports LTV and cash analysis |
| Variable costs | Delivery, payment, support, fulfillment, or usage costs | Converts revenue into contribution profit |
| Retention or repeat rate | Observed customer behavior by cohort | Controls the LTV forecast |
| Refunds and discounts | Reductions from billed or expected revenue | Keeps value estimates realistic |
Keep taxes such as VAT or sales tax out of revenue when they are collected on behalf of a tax authority. Similarly, distinguish a gross revenue LTV from a contribution LTV in separate columns. If attribution is uncertain, show a range or use conservative and expected scenarios rather than presenting one precise number.
For a practical cohort worksheet, create columns for cohort month, channel, campaign spend, new customers, first-order revenue, repeat revenue, variable costs, contribution profit, cumulative contribution profit, CAC, LTV estimate, ratio, and payback month. This structure can be added to a broader business spreadsheet template or KPI dashboard.
Worked examples
Ecommerce example
Suppose a campaign spends $6,000 and acquires 200 new customers. CAC is $30. If the average order value is $75, customers purchase 1.8 times on average, and the contribution margin is 40%, estimated contribution-based LTV is $54:
$75 × 1.8 × 40% = $54
The LTV to CAC ratio is 1.8 to 1. This result should be tested against refunds, discounts, shipping costs, and the time required to generate repeat orders. If repeat purchases have not matured, label the $54 as a forecast rather than an observed LTV.
SaaS example
A subscription product charges $120 per month. Assume monthly churn is 4%, contribution margin is 75%, and CAC is $1,200. The simple expected lifetime is 25 months, so estimated contribution LTV is $2,250:
$120 × 25 × 75% = $2,250
The LTV to CAC ratio is 1.875 to 1. Monthly contribution profit is $90, producing an estimated payback period of 13.3 months:
$1,200 ÷ $90 = 13.3 months
This payback result may be more informative than the ratio if the business must fund implementation, support, or service delivery before the customer becomes profitable.
Service business example
A service firm spends $4,000 on marketing and sales activity and wins 10 new clients, giving it a CAC of $400. Each client is expected to generate $2,000 in billed revenue over the relationship. After contractor costs, payment fees, and other variable delivery costs, the contribution margin is 50%, giving an estimated LTV of $1,000. The ratio is 2.5 to 1.
For services, include the capacity cost of delivering the work in your contribution calculation. A high LTV is less useful if the business cannot deliver the work without hiring, delaying projects, or reducing quality.
For related planning, a contribution margin calculator can help connect customer economics to break-even volume. The business marketing ROI calculator is useful when the question is total campaign return rather than customer-level economics.
When to recalculate
Recalculate CAC, LTV, and payback after a meaningful change in the inputs, not only at year-end. Review the model after a pricing change, discount change, new advertising channel, sales compensation change, onboarding redesign, or shift in fulfillment or support costs. Revisit it during each monthly close and compare new-customer cohorts with older cohorts as retention data matures.
Update the model when advertising costs, platform fees, payment costs, or other variable costs change. Do not overwrite historical results; preserve the original assumptions and add a new scenario or version. This makes it possible to explain why the ratio moved.
Use three scenarios for planning: conservative, expected, and upside. Vary the assumptions that matter most, such as conversion rate, CAC, churn, purchase frequency, contribution margin, or retention. Then set an action for each result: reduce spend if payback exceeds the cash target, improve onboarding if early churn rises, adjust pricing if contribution margin falls, or allocate more budget only when cohort evidence supports it.
Finally, record definitions beside every KPI. State whether CAC includes sales payroll, whether LTV uses revenue or contribution profit, which customers are included, and whether the calculation is cohort-based or blended. Clear definitions make the calculator repeatable and keep the metric useful when campaigns, prices, and operating costs change.
