CAC & Payback Period Calculator

What this calculator does

This tool calculates what it costs to acquire one customer (CAC) and how many months it takes for that customer to pay back the cost. Enter your sales and marketing spend, the customers it produced, and your per-customer economics. It's built for owners deciding how hard to push on growth — and whether their acquisition spending is actually sustainable.

How it works

CAC = total sales & marketing spend ÷ new customers acquired in the same period. It's the all-in average cost to win one customer.

Payback = CAC ÷ (monthly revenue per customer × gross margin). It tells you how many months of that customer's gross profit it takes to recover what you spent to acquire them.

A worked example

If you spent $50,000 to acquire 100 customers, each paying $100/month at an 80% gross margin:

It takes about six months of that customer's gross profit to earn back the $500 you spent to win them. Everything after that is contribution toward profit.

How to read your result

Shorter payback is better — it means your growth spending recycles into cash faster and you depend less on outside capital. For SMB and subscription businesses, a payback under ~12 months is commonly considered healthy, and under 6 is strong. Long paybacks aren't automatically bad if customers stay for years, but they tie up cash and raise risk. Pair this with LTV:CAC for the full picture.

Common mistakes

• ·Leaving costs out of spend. True CAC includes ad spend, sales salaries and commissions, tools, and agency fees — not just media cost.
• ·Using revenue instead of gross profit for payback. You recover cost out of margin, not top-line revenue; using revenue understates payback time.
• ·Averaging across very different channels. A blended CAC can hide one channel that's wildly efficient and another that's losing money.

Frequently asked questions