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Glossary · Unit economics

Payback period

The time for a customer's contribution margin to repay their acquisition cost. Almost always longer than the board believes, because CAC excludes onboarding and blended metrics flatter it.

  • Reviewed
  • 2 min read
  • Part of the 14 term glossary
  • Median finding $58k a year across 74 audits
01

What Payback period means

The payback period, often called CAC payback, is the number of months a customer takes to repay what it cost to acquire them. Divide the customer acquisition cost by the contribution margin the customer produces each month, and the result is how long the business is out of pocket before that customer starts adding profit.

Two shortcuts make it look shorter than it is. The first divides by monthly revenue instead of monthly contribution margin, which ignores every variable cost the customer causes. The second uses a CAC that counts media alone and leaves out onboarding, sales time and incentives. Each shortcut can halve the reported figure, and the two often appear together.

02

The Payback period formula and a worked example

The formula and an illustration; the corpus line is the audited figure behind it.

Payback period = CAC ÷ monthly contribution margin per customer

Worked example Illustration, not a client figure

A $400 CAC against $25 of monthly contribution margin pays back in 16 months. The deck that used $50 of monthly revenue instead of margin said 8.

03

Why Payback period matters in an audit

In an audit, payback is rebuilt from both ends. CAC is loaded fully from the ledger, and the monthly figure it is divided by is contribution margin per customer, cohort by cohort, not average revenue. The rebuilt payback period is then set against how long customers actually stay: a 16 month payback on customers who stay 12 months on average never pays back at all.

Payback matters most to businesses that fund growth from cash, because the period is the time each new customer's acquisition cost sits outside the bank. A payback that is twice what the board believes means the business needs twice the working capital to grow at the same rate, and it usually means some channels or segments are not paying back at all inside the average.

It is also the most direct way to compare acquisition channels. Two channels with the same CAC can have very different payback periods if one brings customers who spend more, churn less or cost less to serve. The audit reports payback by channel and by cohort, which is where the finding usually is.

04

Payback period in the audited cases

Published cases where a customer cost more, or repaid less, than the plan assumed, each with the audited annual figure.

06

Questions about Payback period

What is the payback period?

The payback period, or CAC payback, is the number of months a customer takes to repay their acquisition cost out of the contribution margin they produce. It is CAC divided by monthly contribution margin per customer.

How do you calculate CAC payback?

Divide the fully loaded CAC by the monthly contribution margin per customer. A $400 CAC against $25 of monthly contribution margin pays back in 16 months. Using $50 of monthly revenue instead of margin would have said 8, which is how a payback period ends up twice what the board believes.

What is a good payback period?

One that is clearly shorter than the time customers stay, with room for churn to rise. A payback longer than the average customer lifetime never pays back at all. The audit reports it by channel and by cohort, because the average hides the segments that never repay. Read the CAC page →

Know the term. Now measure it in your own numbers.

Payback period, measured against your own accounts in 5 to 7 working days. $10k to $50k of findings, or your money back.

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Payback period and the wider audit evidence