How to calculate customer acquisition cost, step by step
Customer acquisition cost is one division that answers one question: what does each new customer cost to win? A business that knows the answer can decide whether its marketing pays its way or quietly loses money on every sale. The calculation is the total sales & marketing costs divided by the number of new customers acquired — two numbers from any business’s records, divided into each other. The answer is a plain dollar figure: a CAC of $300.00 means every new customer arrived at a price of three hundred dollars of ads, salaries, software and campaigns.
The formula is CAC = sales & marketing costs ÷ new customers. Sales & marketing costs are everything spent to win customers — the ads, the sales salaries, the marketing software, the campaigns and the events. The cost of serving customers once they arrive does not belong here: support salaries, delivery and hosting are running costs, not winning costs. New customers are the customers won in the same period — first-time buyers only, not repeat orders from people who already bought. Both figures come from the same records, in the same currency, over the same period, or the CAC is wrong before it starts.
The worked example, line by line. Step 1 — the sales & marketing costs: $120,000. Step 2 — the new customers won in the same period: 400. Step 3 — the division: $120,000.00 ÷ 400 = $300.00. Step 4 — the meaning: every new customer costs $300.00 to win. There is no step 5 and no percent to take: the CAC is dollars per customer, never a percent. Work it yourself in the customer acquisition cost calculator.
What the number means
A CAC of $300.00 means each new customer arrived at a price of $300.00 of sales & marketing spend, and the business must earn more than $300.00 from that customer over their lifetime or the growth loses money. A lower CAC means cheaper growth: the same spend winning more customers, or less spend winning the same customers. A higher CAC means the opposite: each win costs more, so the customer must be worth more to justify it. The CAC on its own never says whether $300.00 is cheap or ruinous — that depends on what the customer is worth. A $300.00 CAC against a $3,000 lifetime value is a bargain, and the same $300.00 against a $200 lifetime value is a loss on every sale.
What moves the customer acquisition cost
Two things move the CAC: the costs and the customers. Raise the sales & marketing costs and the CAC rises: at $150,000 of costs the CAC is $375.00, and at $200,000 it is $500.00 — each extra dollar of spend spread over the same customers. Cut the costs and the CAC falls. Win more customers on the same spend and the CAC falls: the same $120,000 spread over more new customers means a smaller share per customer. Win fewer customers on the same spend and the CAC rises, because the same costs now buy fewer wins. The cheapest way to cut the CAC is usually to win more customers without spending more — better targeting, a better offer, or word of mouth that costs nothing at all.
When the CAC is undefined
If the number of new customers is 0, the CAC is undefined — dividing by 0 has no answer. A business that won no customers in a period has no CAC to calculate, only a warning. If the sales & marketing costs are $0, the CAC is $0.00 — a real figure, not undefined: nothing spent, nothing per customer. A negative CAC is possible when the costs are negative, a refund or a bookkeeping credit, but a business that sees one should check the books before trusting it.
Common mistakes
The first mistake is counting repeat customers as new ones — a returning buyer costs nothing to win, so counting them spreads the spend over too many customers and the CAC comes out too low. The second is leaving costs out — the sales salaries and the marketing software count just as much as the ads, and a CAC built on ads alone flatters the business. The third is mixing periods — the costs from one quarter divided by the customers from another is not a CAC at all. The fourth is forgetting that the CAC says nothing about what the customer is worth — a low CAC is no good if the customers leave after one order. Work it out in the customer acquisition cost calculator, and check the customer lifetime value calculator and the gross margin return on investment calculator before you decide the growth pays.