Understanding Incrementality: The Secret to Scaling Profitably

If you want to scale your ecommerce brand without burning money, you need to master one concept above all:

Incrementality.

It’s not flashy. It doesn’t show up in your ROAS dashboard. And most media buyers either ignore it or don’t understand it.

But incrementality is what separates real growth from wasted spend.
It’s how you know what’s actually working when you scale, and how far you can push.

Let’s break it down in plain English.

What Is Incrementality?

Incrementality is the measure of the additional value your marketing generates beyond what would’ve happened anyway.

It answers the critical question:

“If I hadn’t run this ad, would I still have gotten this sale?”

If yes, your marketing isn’t incremental.
If no, your marketing is working because it created net new impact.

Here’s the problem: most brands don’t test for this. They see revenue, and assume it’s from their campaigns. But often, that spend is just capturing revenue that would’ve come in anyway through organic, email, or returning customers.

Why Incrementality Matters for Scaling

When you’re spending $10K/month, ROAS is a decent proxy for performance.

But when you try to scale to $100K/month? ROAS becomes a blunt tool. Here’s why:

• ROAS includes all revenue, including from returning customers.
• It doesn’t show diminishing returns as you increase spend.
• It can mask non-incremental performance, where more spend doesn’t actually drive more growth.
  
  

Incrementality gives you the signal behind the noise.

It tells you:

• When to push spend
• When to pull back
• When your campaigns are creating value, and when they’re not
  
  

Visualizing the Concept: ROAS Decay & The Sweet Spot

Let’s use a simplified curve:

As you scale spend…

• ROAS will drop
• CAC will rise
• But revenue and contribution margin can still increase, for a while
  
  

Then you hit a point of diminishing returns where each extra dollar brings less and less new value.

That’s your incrementality threshold.

Most brands hit this point and panic. They pull back.
Smart brands test for it, understand it, and scale within the guardrails.

Real Example: Incrementality in Action

From the book:

Notice what happens:

• At 5x ROAS, profit is still high, customer acquisition is strong.
• At 4x, revenue levels off, and profit begins to dip.
• At 3x, you’re overspending, profit erodes, and CAC spikes.
  
  

This is the data that tells you exactly where your ceiling is.
ROAS alone would never show this.

How to Track Incrementality (Without a Data Science Team)

You don’t need a PhD or advanced tech stack to apply this thinking. Start simple:

1. Baseline your key metrics: CAC, revenue, new customers, contribution margin.
   
   
2. Scale budget gradually (e.g., +20% every 2 weeks).
   
   
3. Watch how those metrics change:
   
   • Are you getting more new customers?

1. • Is CAC stable or climbing?

1. • Is your contribution margin holding?
     
     
2. Chart it. Look for inflection points.
   
   

If you’re getting more customers at a profitable CAC, you’re in the zone.
If customers flatten and CAC spikes, you’ve pushed too far.

Common Pitfalls

• Chasing the same ROAS as you scale
  → You’ll stop growing before you hit your potential.
  
  
• Mistaking returning customer revenue for growth
  → Use first-time purchase tracking to separate new from repeat.
  
  
• Assuming a great ROAS = great performance
  → It might just be efficient, not incremental.
  
  

This Is the Work of a Growth Operator

Scaling isn’t about protecting ROAS.

It’s about knowing how far you can go before you hit diminishing returns, and how to ride that edge profitably.

That’s the work of a real ecommerce growth leader or media buyer.

So ask yourself:

• Do you know your incrementality curve?
  
  
• Are you spending confidently or are you guessing?
  
  
• Do you have someone on your team who’s watching this?
  
  

If not, you’re probably underspending, or overspending, and leaving money on the table either way.

Explore Human’s Ecommerce Marketing Services

We build scalable customer acquisition systems based on incrementality. Not just ratios.
👉 See how we help brands grow smarter, not just harder

Read the Book: Why High ROAS Is Bad for Your Ecommerce Business

This chapter changed how dozens of our clients view paid media.
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