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Guide

How to Measure Incremental ROAS

Incremental ROAS is the return on the sales your advertising actually caused, not the sales it was merely present for. It is almost always lower than the ROAS your ad platform reports, because the platform counts conversions that would have happened anyway. This guide covers what incremental ROAS is, the formula, a worked Shopify example, and the two ways to measure it without guessing.

By , Founder & CEOUpdated

Reported ROAS vs incremental ROAS

Reported ROAS = attributed revenue divided by spend, where attributed is decided by the platform's own rules. Incremental ROAS = caused revenue divided by spend, where caused means the orders that would not have occurred without the channel.

A channel can show 5x reported and 1.4x incremental. Same spend, completely different decision.

The incremental ROAS formula

Incremental ROAS = (revenue with the channel - revenue that would have happened without it) / spend.

The hard term is the counterfactual - revenue without it - which you never directly observe. Measuring incrementality is, in practice, the work of estimating that counterfactual credibly.

A worked Shopify example

Say a brand spends €10,000/month on a retargeting channel reporting €51,000 in sales (5.1x). Much of that audience already intended to buy. Estimating the counterfactual from sales history shows ~€14,000 would not have happened otherwise.

€14,000 / €10,000 = 1.4x incremental ROAS. The reported number said scale it. The incremental number said it is barely paying for itself.

Two ways to measure it

  1. Holdout/geo tests - suppress the channel for a group and compare. Accurate but slow and costly (see the geo testing guide).
  2. Causal modeling on historical data - estimate the counterfactual from variation already in your Shopify + GA4 history, in minutes. Causality Engine's read works this way and shows what each channel caused, next to last-click.

Frequently asked questions

  • Why is incremental ROAS lower than platform ROAS?
    Because platform ROAS includes conversions that would have happened anyway; incremental ROAS removes them.
  • Can I measure incremental ROAS without a holdout?
    Yes. Causal modeling estimates incrementality from your existing sales history, no test required.
  • What is a good incremental ROAS?
    Anything confidently above 1.0x is paying for itself; the confidence interval tells you how sure to be.

The pillar this guide links up to: Incrementality Testing

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