Two channels. Identical math. One honest answer.
Put your real paid-channel numbers next to a two-sided referral program — both counted the same way, both taken through to payback months. In your browser, no signup.
Paid channel
Referral channel
Both channels
- Customers / month
- 33.3
- Channel cost / month
- $10,000
- Payback
- 0.9 mo
- Customers / month
- 24.0
- Channel cost / month
- $4,800
- Payback
- 0.6 mo
On these numbers a referred customer costs $100 less than a paid one and pays back 0.3 months sooner. The structural reason: referral CAC is a fixed reward paid only on conversion, while paid CAC carries every click that never converted.
What this deliberately leaves out: referred customers' higher retention and value (the best evidence puts it at 16%+), which makes the referral column conservative. And the two channels aren't rivals — referral volume scales with the customer base that paid spend builds.
Modelling program revenue rather than channel cost? That's the ROI calculator. Setting the reward this comparison depends on? The reward planner. The metric definitions live on referral program metrics.
How do you calculate referral CAC?
Add everything you paid per converted referral — the referrer's reward and the friend's incentive — and that sum is the acquisition cost. In a well-built program it's practically fixed: rewards pay only on conversion, so a referral that never converts costs nothing, which is the structural difference from paid.
Counting only the referrer's side is the standard flattering mistake. The friend's discount buys the same thing ad spend buys — a new customer's decision — and belongs in the same line.
Why compare payback months rather than CAC alone?
Because a cheap customer who takes fourteen months to repay their cost can strain cash more than a pricier one repaying in three. Dividing each channel's CAC by monthly gross margin per customer puts both on the axis finance actually plans around: months until the customer has paid for themselves.
What does this comparison deliberately leave out?
Referred customers' higher retention and value — the best evidence puts them at least 16% more valuable with better retention — which makes the referral column conservative. It also isn't a rivalry: referral volume scales with the customer base paid spend builds, so the honest reading is a portfolio, not a winner.
Is this CAC comparison calculator free?
Yes — free, no signup, computed entirely in your browser.
Why is my referral CAC exactly the two rewards added together?
Because rewards pay per converted referral, the cost per customer IS the combined reward. If your program also carries platform fees you want amortised in, divide monthly platform cost by monthly referred customers and add it — the structure stays the same.
What is a good CAC payback period?
Common SaaS practice treats under 12 months as healthy and beyond 18 as strained, but the honest benchmark is internal: each channel against your others, and the trend over time. This tool exists to make that internal comparison with the same math on both sides.
The referral column needs a program behind it
ReferralFlo runs the asks, links, attribution and reward payouts that turn the right-hand column from a model into a channel.