What customer acquisition cost means
Customer acquisition cost (CAC) is the cost of acquiring a new customer over a defined period or campaign. For ecommerce sellers, it helps answer whether paid advertising, affiliate commissions and other acquisition activity are bringing in customers at a cost the business can recover.
The basic CAC formula
CAC = attributable customer acquisition spend ÷ number of new customers acquired.
For example, if a campaign costs $2,400 and generates 80 first-time customers, CAC is $30 per new customer. Use new customers in the denominator—not total orders—because repeat orders from existing customers do not represent new customer acquisition.
Define what spend you include
A narrow paid-media CAC may include only ad spend. A fully loaded acquisition CAC may also include agency fees, campaign tools, creative production, affiliate commissions, influencer payments and the portion of staff costs attributable to acquisition. Neither definition is automatically correct for every decision. State the scope and use it consistently when comparing channels.
Calculate break-even acquisition cost
For a first-order break-even view, calculate the contribution available before acquisition cost. Break-even CAC per new customer = expected first-order contribution before acquisition. If a new customer’s first order produces $22 of contribution before marketing, spending $22 to acquire that customer leaves zero contribution from that first order before fixed overhead, taxes and financing costs.
Suppose first-order net sales are $60 and product, inbound freight, fulfilment, marketplace/payment fees and other variable costs total $38. First-order contribution before acquisition is $22. If CAC is $30, the first order contributes negative $8 after acquisition. That does not prove the campaign is unprofitable over the customer relationship, but it does mean the business is relying on future purchases to recover the acquisition investment.
Use repeat purchases carefully
You can estimate a longer payback window by adding expected contribution from repeat purchases within that window. Use probability-weighted repeat contribution, not the full theoretical lifetime value. For example, if the first order contributes $22 and the expected contribution from repeat orders over the next 90 days is $8, the 90-day break-even CAC is $30. This estimate is only as reliable as the cohort and repeat-purchase data behind it.
Connect CAC with ROAS
Return on ad spend (ROAS) is advertising-attributed revenue divided by ad spend. ROAS is not profit: it ignores product cost, marketplace fees, fulfilment, refunds and other expenses unless those are explicitly included in the metric. A campaign can report strong ROAS while losing money after variable costs. Read the break-even ROAS guide and use the break-even calculator to test the cost assumptions.
Measure cohorts and attribution consistently
- Define the attribution window and channel rules before comparing campaigns.
- Separate first-time customers from returning customers.
- Account for refunds, cancellations and invalid orders where data is available.
- Compare CAC with contribution over the same time horizon.
- Watch for overlapping attribution between marketplaces, paid search, social ads and affiliates.
- Track customer cohorts so repeat-purchase assumptions are based on observed behavior.
Common mistakes
Do not divide advertising spend by orders when the decision concerns new-customer acquisition. Do not compare a paid-media-only CAC with a fully loaded CAC without labeling the difference. Do not use gross revenue or unadjusted lifetime value as if it were cash contribution available to repay acquisition costs.
Practical decision rule
Set an allowable CAC based on the contribution you expect to earn within a clearly defined payback period, then monitor actual cohort results. A lower CAC is not always better if it brings low-retention customers, and a higher CAC is not automatically acceptable because a forecast assumes repeat purchases. Use observed order economics and repeat behavior to update the limit.
Record realised costs by order in the free order profit tracker. The product profit calculator can help estimate contribution before acquisition cost.
Compare acquisition cost by channel
Calculate a separate CAC for each channel using the same customer definition, date range and attribution rules. For example, if paid search spend is $1,200 and it brings 40 first-time customers, paid-search CAC is $30. If social spend is $900 and it brings 20 first-time customers, social CAC is $45. These figures are only comparable when both channels use the same attribution window and include the same cost categories.
Keep a simple channel record with spend, first-time customers, CAC, first-order contribution and contribution recovered within your chosen payback window. A channel with a higher CAC may still be viable if its customers generate stronger repeat contribution, but validate that with observed cohort data rather than an assumed lifetime value.
Financial note
This guide provides a management-planning framework, not a guarantee of campaign performance or financial advice. Attribution systems differ and may over- or under-credit individual channels. Reconcile campaign data with marketplace orders, refunds and actual costs before making material spending decisions.