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The New Growth Formula: Why CAC Targets Beat ROAS for E-Commerce Success

Moving Beyond ROAS: How CMO-Level Math Unlocks Sustainable E-Commerce Growth

Moving Beyond ROAS: How CMO-Level Math Unlocks Sustainable E-Commerce Growth

As someone who’s managed hundreds of clients across diverse verticals, I’ve seen a recurring challenge: advertisers remain locked into simplistic metrics like ROAS and platform-reported conversions when measuring success. While return on ad spend (ROAS) can serve as a starting point, it often obscures the bigger picture—hiding issues around new customer acquisition costs, repeat buyer behavior, and true profitability.

In this article, I want to share a strategic framework I call “CMO-level math,” a perspective forged from hands-on experience managing over $200 million in annual Google Ads spend across about 175 industries. This approach will help you:

  1. Understand customer acquisition cost (CAC) as a key performance indicator.
  2. Leverage tools to analyze average order value (AOV), purchase frequency, and profit margins.
  3. Employ media efficiency ratios (MER) and external attribution platforms for holistic insights.
  4. Identify how different channels—Google, Meta, YouTube, and others—can complement each other instead of working in isolation.

Ultimately, this framework ensures that you scale profitably by focusing on what truly matters: net profitability and sustainable business growth.

Step 1: Establishing a CAC Target Using Real Customer Data

Before you even launch your campaigns, you need to know how much you can afford to spend to acquire a first-time customer. Traditional ROAS goals—like the common but arbitrary “4x ROAS”—don’t account for factors like margin, repeat purchase rates, and customer lifetime value (LTV).

Recommended Tools:

  • By the Numbers (Shopify App):
    By the Numbers is a powerful Shopify analytics tool that scans your entire store history, providing insights into AOV, purchase frequency, and first-time vs. returning customer splits.
    (If you’re not on Shopify, consider using Google Analytics 4 plus a custom spreadsheet or a similar analytics platform.)

Key Metrics to Extract:

  1. Average Order Value (AOV):
    For example, let’s say your store’s AOV is $45.70.
  2. Purchase Frequency (PF):
    If customers buy 1.13 times on average over a given period, multiply the AOV by PF. In this example, $45.70 * 1.13 ≈ $51.64. This is your average customer value over the period analyzed.
  3. Profit Margin (PM):
    Assume a 65% profit margin on your product. Multiply $51.64 * 0.65 ≈ $33.56. This is the maximum you can spend to acquire a customer (your CAC target) without losing money over that timeframe.

Why This Matters:
A CAC-based approach focuses on acquiring first-time customers at break-even or better. If you keep acquisition costs at or below $33.56 in this scenario, every new customer added should yield profit over time—especially as repeat customers return without additional acquisition spend.

Step 2: Tracking New vs. Returning Customers and Their Impact on Profitability

Merely hitting a ROAS target doesn’t tell you if you’re scaling profitably. A steady influx of new customers builds a base that repeatedly purchases in the future, increasing the long-term value of your customer pool.

Recommended Tools:

  • Northbeam:
    Northbeam consolidates and analyzes data across all channels, showing new vs. returning customers, CAC, and MER (Media Efficiency Ratio). You can understand how first-time buyers enter the funnel and how returning customers contribute over time.
  • Triple Whale:
    Another option like Triple Whale offers insights into customer cohorts and LTV, giving you clarity on how first-time buyers convert into loyal patrons.
  • Wicked Reports:
    Wicked Reports focuses on multi-touch attribution and LTV, helping you see which channels drive long-term growth beyond the initial click.

What to Look For:

  • First-Time Customer CAC: If your first-time CAC is around $30 (below the $33.56 threshold), you’re acquiring customers profitably.
  • Repeat Purchase Rates: A strong return customer rate—say 30%—creates a snowball effect. As you scale first-time acquisitions at break-even CAC, the repeat buyers deliver profitable sales at zero acquisition cost, compounding your returns over time.

Step 3: Embrace MER Over ROAS for a Top-Down Perspective

ROAS measures return from a single channel relative to that channel’s ad spend. However, it misses the bigger picture—customers often see multiple ads across channels before purchasing. MER (Media Efficiency Ratio)—total revenue divided by total ad spend—provides a macro-level view.

Recommended Tools:

  • LifeTimely:
    LifeTimely integrates with Shopify and includes cost of goods sold (COGS), fees, and operating expenses, delivering a full profit and loss (P&L) perspective. By comparing your MER to net profit, you validate if your blended CAC and spend levels are genuinely healthy.
  • Northbeam or Measured for Incrementality:
    Measured helps isolate incremental impact, ensuring you know which channels drive genuinely new conversions rather than recycling existing customers.

What to Look For:

  • Stable or Improving MER: A stable 2x MER overall may be sufficient if your first-time CAC is on target and return customers continue growing. You don’t always need a 4x ROAS if the long-term math checks out.
  • Profit Trends: Validate MER against net profit in LifeTimely. If your MER is stable and you’re consistently net-profitable, you’re scaling correctly—even if ROAS looks modest.

Step 4: Understanding Channel-Specific Benchmarks for CAC

YouTube, Meta (Facebook/Instagram), Google Ads (Performance Max, Shopping), and Bing will each have different CAC benchmarks. YouTube might be higher due to a less direct response-oriented environment, while Google Shopping might yield a lower CAC due to high intent.

Recommended Steps:

  1. Clicks-Only Attribution for Baseline:
    Start by examining click-attributed conversions in Northbeam or your chosen attribution tool. This strips away view-through conversions, giving a conservative baseline for each channel’s performance.
  2. Identify Benchmarks:
    • Facebook might give you a $60 CAC click-only.
    • Google might yield a $30 CAC.
    • YouTube might be $140 CAC in direct clicks.
    These numbers aren’t “bad” or “good” in isolation—they’re reference points. If you double spend on YouTube and that $140 CAC stays roughly consistent while your overall blended CAC remains near $30, it means YouTube is assisting conversions elsewhere (brand search, direct, and organic).
  3. Adjust Expectations Per Channel:
    Don’t demand the same CAC from YouTube as you do from Google Shopping. Each channel contributes differently to the funnel. What matters is that when you push more on these top-of-funnel channels, your overall MER and first-time CAC remain stable or improve.

Additional Resources:

Step 5: Avoiding the ROAS Trap

Many advertisers cling to ROAS without considering profit margins, repeat customers, and cost structure. But a “great” ROAS can hide inefficiencies—like overspending on returning customers you’d have gotten for free or at lower cost through email or organic traffic.

How to Evolve Beyond ROAS:

  • Incorporate Incrementality Tests:
    Use platforms like Measured or Rockerbox to run incrementality studies. Identify which channels truly bring in net-new customers rather than redistributing credit.
  • Reduce Brand Campaign Reliance:
    Brand keywords in Google Ads often show spectacular ROAS. But they capture mostly existing customers or people who already know your brand. Consider using Manual CPC Bidding without eCPC to control brand costs. Aim for an optimal Absolute Top Impression Share at minimal bid, ensuring you’re not overspending on those who would convert anyway.

Conclusion: Data-Driven, Profit-Focused Scaling

Moving beyond ROAS means viewing your advertising as a holistic ecosystem. By focusing on first-time CAC targets derived from actual store data, tracking new vs. returning customers, and cross-referencing top-line MER with net profitability, you gain a sustainable path to scale.

This CMO-level math acknowledges that not all sales are equal. Some are strategic investments in your brand’s future (first-time customers), while others are “free” profits from loyal repeat buyers. By embracing a broader perspective, employing the right analytics tools, and setting realistic channel-specific benchmarks, you can confidently invest in growth that remains profitable and resilient—even in competitive markets.

Additional Recommended Links for Further Learning:

By aligning your marketing strategy with true CMO-level math, you’ll transcend the old ROAS mindset and unlock sustained growth anchored in profitability and long-term customer value.

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