How to use it
Tap CAC, Spend or Customers in the equation to choose what to find. Enter the spend in one currency and the customer count for the same dates. The calculator also works the other way round: give it a target CAC and a budget, and it tells you how many customers that budget has to win.
The formula
CAC = spend ÷ new customers
Spend = CAC × new customers
New customers = spend ÷ CAC
Shopify describes it as adding up all the costs of acquiring new customers in a period and dividing by the number of new customers who bought in that period. HubSpot's version names the two cost buckets: CAC = (cost of sales + cost of marketing) ÷ number of new customers.
What to put in "spend"
The formula is simple. The arguments are about what goes on top of the line.
- Paid media only. Ad spend divided by new customers. Easy to pull from ad platforms, but it flatters the number because it leaves out the people and tools behind the ads.
- Marketing costs. Ad spend plus agency fees, content, software and the marketing team's pay.
- Sales and marketing. Everything above plus sales salaries, commissions and sales tools. This is the "fully loaded" CAC that HubSpot's formula describes.
None of these is wrong; they answer different questions. Paid-only CAC tells you whether a channel pays for itself at the margin. Fully loaded CAC tells you whether the business does. Write down which one you used, and use the same one when you compare months or compare with lifetime value.
CAC and CPA
Cost per acquisition uses the same division with a different count underneath. An "acquisition" is whatever you defined as a conversion: a sale, a lead, a trial sign-up. With Google Ads' Target CPA bidding you set the average cost per conversion you want. So CPA describes one campaign's conversions, and CAC usually describes all of the company's new paying customers. If every conversion is a new customer, the two are the same number.
Worked examples
Finding CAC. $18,000 spent in a quarter, 240 new customers in that quarter. $18,000 ÷ 240 = $75.00.
HubSpot's example. $300,000 cost of sales plus $100,000 cost of marketing, and 500 new customers: $400,000 ÷ 500 = $800.00.
Customers a budget must win. You have $10,000 and want CAC to stay at $80 or less. $10,000 ÷ $80 = 125 customers.
Spend a target allows. You aim to win 300 customers at $75 each: $75 × 300 = $22,500.
| Spend | New customers | CAC |
|---|---|---|
| $18,000 | 240 | $75.00 |
| $400,000 | 500 | $800.00 |
| $10,000 | 125 | $80.00 |
Timing and attribution
Spend and customers rarely line up neatly. A business with a long sales cycle pays for this month's ads and wins the customers next quarter. Two common fixes: lag the customer count by your typical sales cycle, or measure over a longer window so the edges matter less. Also decide whether customers who arrived with no paid touch (word of mouth, returning visitors) count in the denominator. Including them lowers CAC; excluding them gives a "paid CAC" that is closer to the cost of the next customer you buy.
How this calculator handles your numbers
Spend and CAC are money; customers must be a whole number. The arithmetic runs on exact fractions, and money is rounded to two decimals at the end, half away from zero. If the answer is a customer count that doesn't come out whole, it is rounded to the nearest customer and the exact figure is shown. Zero customers or a zero CAC, where dividing makes no sense, give a message instead of a number.