Contribution-Margin Payback Period over CAC
Judge acquisition ROI by how many months of contribution-margin profit it takes to repay CAC, not by CAC or LTV:CAC.
- Difficulty
- Moderate
- Time to result
- ~weeks to results
- Steps
- 3
- Confidence
- 90%
CAC alone optimizes cost, not value, so cutting it often just attracts cheaper, lower-value customers. LTV:CAC fixes the value blind spot but relies on hard-to-predict, assumption-laden LTV that can destroy value when early churn assumptions prove wrong. Batchu prefers payback period measured in contribution margin: how many months of per-customer profit (after all variable costs) it takes to repay acquisition cost. Its assumptions are grounded in recent data and can be re-evaluated quickly.
Origin
Sri Batchu's preferred growth-efficiency metric, applied at Ramp (only four years old at the time), reasoning from the weaknesses of CAC and LTV-based metrics.
Core principles
- 01CAC optimizes cost, not value, and can pull in worse customers
- 02LTV is a DCF-like, assumption-laden forecast that misleads when churn is underestimated
- 03Payback period uses recent, verifiable data and can be re-evaluated quickly
- 04Use contribution margin, not revenue or gross margin
- 05The acceptable payback period is a mandate set at executive/board level
How to run it
- 1
Compute contribution margin per customer
Take per-customer revenue and subtract all variable costs - cost of production plus other costs to serve such as support - to get the profit that scales with revenue.
Watch out Use contribution margin, not revenue or gross margin, so you are counting real per-customer profit.
- 2
Divide CAC by monthly contribution-margin profit
Payback period is simply how many months of that profit it takes to repay acquisition cost (e.g. $5,000 CAC / $500 monthly profit = 10-month payback).
- 3
Set a target payback and drive blended payback down
Leadership sets the payback period the company is comfortable with, then everyone orients toward driving the blended payback period down as much as possible.
Pro tip Because payback assumptions are recency-based, revisit them frequently rather than trusting a long-horizon LTV forecast.
Watch out Optimizing LTV:CAC when churn is underestimated can make you overspend and destroy value once real retention data arrives.
In the wild
Batchu warns that if you assume low churn and high LTV, your LTV:CAC looks great and you spend heavily; then a year or two in you discover churn is higher than thought and early customers weren't representative, and you've destroyed a lot of value. Payback period avoids this by relying on near-term, checkable numbers.
→ A more robust efficiency metric for young companies that cannot yet credibly forecast lifetime value.
Common mistakes
Chasing lower CAC
Reducing CAC optimizes cost while ignoring value, so you succeed at lowering CAC but bring in less valuable customers - the ones you can attract cheaply.
Anchoring spend to optimistic LTV
LTV is assumption-laden; if your churn turns out higher than assumed, an attractive LTV:CAC leads you to overspend and destroy value before you realize the error.
Is it for you?
Best for
Growth and finance leaders at young companies without enough history to forecast LTV credibly
Not ideal for
Mature businesses with long, well-validated retention curves where LTV can be estimated with confidence
From the transcript
“when you focus on CAC and reducing CAC what tends to happen is you uh actually might be doing something very damaging where you're succeeding…”
“especially if you think your turn is low and your LTB is very high you might end up spending a lot of money because you're…”
“payback period is literally just how many months of that profit uh would it take to pay”
From the episode
Lessons from scaling Ramp
Sri Batchu (Ramp, Instacart, Opendoor)