Payback Period (meses)

Payback period in months

Payback counts the months you need to earn back an investment from the cash flow it throws off: payback = investment / monthly cash flow. In SaaS the usual flavor is CAC payback = CAC / (ARPU × gross margin). Say your CAC is R$600, ARPU is R$150 and margin sits at 60%. That leaves R$90 of monthly contribution, so the payback lands around 6.7 months. As a SaaS rule of thumb, CAC payback under 12 months is healthy and under 6 is excellent. Watch the catch, though: simple payback says nothing about the time value of money. When that matters, reach for Discounted Payback, which applies the discount rate to each future cash flow.

Applications

It shows up in SaaS unit economics, capex calls, board decks, and the question of how much CAC a business can stomach. The number lets you line up projects of similar risk against each other and put a ceiling on what you'll spend to acquire a customer. Once payback creeps past 18 months, your runway and LTV/CAC ratio usually can't carry the growth.

FAQ

Payback or LTV/CAC? You want both. Payback tells you how fast the money comes back, which is your cash risk; LTV/CAC tells you the total return. A 3:1 LTV/CAC paired with a 24-month payback can still drain your cash flow.

Why use gross margin, not revenue? You recover CAC out of contribution margin, not out of gross sales. Plug in ARPU straight and you'll understate the payback for any low-margin product.

Does churn affect payback? Not in the formula, but yes in practice. High churn cuts the customer lifetime short, so when your payback sits close to the average lifetime, take it as a red flag.