If you could only use two data points to evaluate a business’s health, you’d probably choose customer lifetime value (LTV) and customer acquisition cost (CAC). In other words, you’d want to know how much money, on average, a customer will spend at the business—and how much it cost to acquire them in the first place. Pretty straightforward, right?

Not so fast.

Using acquisition cost to track performance comes with a big caveat: There are different ways of interpreting and measuring CAC, and you need to be sure you’re using the right formula for your needs.

If you're a founder raising capital or an investor: fully loaded CAC

In this case, you need the most comprehensive interpretation of CAC possible. That’s fully loaded CAC, which may sound like a pizza order, but is actually a measurement that includes every single cost associated with your acquisition effort.

Fully loaded CAC = Total cost of everything associated with acquisition / Total net new customers.

When I say everything, I mean everything. Fully loaded cost includes:

The process of defining and gathering all this data is time-intensive, complicated work. Whose salaries should be counted? What about an employee who handles both customer service and other administrative tasks? How do you determine what percentage of your technology is used for acquisition?

Fully loaded CAC is overkill for marketers. But if you’re trying to raise capital—or, conversely, if you’re kicking the tires to see if a business is worth your investment—these details might matter. The customer LTV to fully loaded CAC ratio is a clear measure of how efficiently the business can scale. It’s also worth checking over time, to see how the ratio changes. Many businesses find that CAC increases eventually, as they acquire high-intent prospects first, then have to work harder to convert new customers. Of course, if that increase is offset by higher customer LTV, you’re still in good shape.

If you're a marketing manager: blended and/or paid CAC

Marketers use CAC to evaluate growth channels and allocate resources, and you can get a good enough measure without spending weeks crunching numbers. The key is establishing parameters and maintaining them over time, so you’re always measuring apples to apples.

There are two CAC models that make sense for marketers: blended and paid. Let’s look at blended CAC first.

Blended CAC = Sales and marketing expenses (excluding salaries and overheads) / Total new customers acquired.