Monthly Customer Acquisition Cost Formula
Learn how to calculate monthly customer acquisition cost by dividing total acquisition spending by new customers gained.
Monthly customer acquisition cost (CAC) estimates the average amount spent to gain each new paying customer in a reporting month. Tracking the same cost categories and customer definition each month makes the result more useful for monitoring acquisition efficiency.
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Monthly Customer Acquisition Cost
Where:
Add the acquisition-related costs for the month, then divide the total by the number of new customers acquired in that same month.
Variables Explained
| Variable | What It Means | Unit |
|---|---|---|
| advertisingSpend - Monthly advertising spend | Paid media and advertising costs incurred during the reporting month. | currency |
| marketingPayroll - Marketing payroll allocated to acquisition | The acquisition-related share of marketing salaries, wages, and benefits. | currency |
| salesPayroll - Sales payroll allocated to acquisition | The acquisition-related share of sales compensation, commissions, and benefits. | currency |
| otherAcquisitionCosts - Other acquisition costs | Relevant agency fees, software, events, referral payments, and campaign costs. | currency |
| newCustomers - New customers acquired | The number of new paying customers gained in the same month. | number |
Step-by-Step Calculation
Set the reporting period
Use one defined month for every cost input and for the new-customer count.
reportingPeriod = 1 month
Total advertising and marketing payroll
Combine paid advertising with the portion of marketing payroll directly related to acquiring customers.
marketingAcquisitionCost = advertisingSpend + marketingPayroll
Add sales payroll and other costs
Include acquisition-related sales compensation and other eligible acquisition expenses.
totalAcquisitionCost = marketingAcquisitionCost + salesPayroll + otherAcquisitionCosts
Count new customers
Count each newly acquired paying customer once using a consistent customer definition.
newCustomers > 0
Calculate monthly CAC
Divide total monthly acquisition cost by new customers acquired in that month.
monthlyCustomerAcquisitionCost = totalAcquisitionCost / newCustomers
Monthly CAC calculation example
Add advertising and marketing payroll
$5,000 + $3,000
$8,000
Add sales payroll
$8,000 + $4,000
$12,000
Add other acquisition costs
$12,000 + $1,000
$13,000
Divide by new customers
$13,000 ÷ 40
$325
Final Result
Estimated monthly customer acquisition cost: $325.00 per customer.
Assumptions
- ✓All included expenses and new customers relate to the same monthly reporting period.
- ✓Only costs connected to acquiring new customers are included.
- ✓Payroll entries represent the acquisition-related portion of total compensation.
- ✓Each customer is counted once under a consistent definition, such as a new paying account.
- ✓Costs and customer records are accurately allocated and recorded.
Limitations
- !A monthly CAC can fluctuate because spending and customer conversions do not always occur in the same month.
- !The calculation shows an average and does not reveal CAC by channel, campaign, product, or customer segment.
- !Long sales cycles may make a single-month comparison less representative of the full acquisition effort.
- !Different customer definitions or expense allocations can make comparisons between periods less reliable.
Common Mistakes to Avoid
Including customer support, retention, or account-management costs when the measure is intended for new-customer acquisition only.
Using leads, trials, or sign-ups instead of new paying customers as the denominator.
Counting customers from a different month than the expenses being measured.
Including all sales and marketing payroll rather than the share attributable to acquisition.
Changing the customer definition or cost categories without noting the change in reporting.
Related Formulas
Frequently Asked Questions
What is the formula for monthly customer acquisition cost?
Monthly CAC equals total acquisition-related spending for the month divided by the number of new customers acquired in that month.
What costs belong in monthly CAC?
Typical inputs include advertising, acquisition-related marketing and sales payroll, commissions, agency fees, campaign software, events, and referral payments when they are tied to winning new customers.
Should sales commissions be included in CAC?
They can be included when the commissions relate to acquiring new customers and are treated consistently in each reporting period.
Can I calculate CAC with zero new customers?
No. Dividing by zero is not possible. Report the acquisition spend separately and calculate CAC once at least one new customer is recorded.
Why is my monthly CAC higher than last month?
It may rise when spend increases, conversion volume falls, or payroll and other cost allocations change. A timing difference between spending and closed customers can also affect it.
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