ROAS vs ROI vs CAC: the only three metrics your P&L reads

Three metrics. One of them tells you if a campaign was profitable. One tells you if the business was profitable. One tells you whether you can afford to grow. Most marketing teams report on all three and act on none of them correctly. This article is the definitional piece we send to every new client before their first monthly review.

ROAS: Return on Ad Spend

ROAS is the simplest of the three. It is the ratio of revenue attributed to advertising to the ad spend that generated it. If you spend $10,000 on ads and they drive $40,000 in attributed revenue, the ROAS is 4.0× — also written as 400%.

ROAS is a media metric. It tells you whether the advertising was efficient in isolation. It does not tell you whether the campaign was profitable for the business — because it doesn't account for cost of goods, operational costs, returns, refunds, or the time value of revenue.

ROI: Return on Investment

ROI is the business metric. It accounts for all the costs that ROAS ignores. If the campaign generated $40,000 in revenue at 60% contribution margin, it contributed $24,000. Subtract the ad spend ($10,000), the creative production ($3,000), and the landing page build ($1,000), and the net contribution is $10,000 — a 71% ROI on the full $14,000 investment.

ROI is what the CFO reads. ROAS is what the media buyer reads. A healthy marketing operation watches both and understands how the two relate.

CAC: Customer Acquisition Cost

CAC is the cost to acquire one new customer, fully loaded. Divide total marketing spend (media plus agencies plus internal salaries plus tools) by the number of new customers acquired in the period.

CAC by itself is meaningless. CAC compared to LTV (lifetime value) is the number that matters. The LTV:CAC ratio tells you whether you can afford to grow. Below 3:1, acquisition is too expensive to scale profitably. Above 5:1, you're probably under-investing in acquisition.

Blended vs paid CAC

Blended CAC includes organic customers (SEO, referral, direct) in the denominator. Paid CAC only counts customers attributed to paid channels. Most teams report blended CAC without saying so, which makes paid-channel performance look better than it is.

Always report paid CAC and blended CAC side by side. If they diverge significantly, your organic engine is either carrying the business or hiding its weakness.

The attribution window matters

ROAS, ROI, and CAC are all sensitive to the attribution window. A 1-day-click ROAS looks worse than a 7-day-click ROAS, but the 7-day window includes customers who would have converted anyway. The right window depends on the product category and the consideration cycle.

For most ecommerce: 7-day-click + 1-day-view. For considered purchases: 28-day-click. For B2B: whatever matches your sales cycle. Pick one, document it, and stop changing it month to month.

How to report all three together

A healthy monthly review looks like this: ROAS by channel (how efficient was the media?), ROI blended (was the marketing operation profitable overall?), CAC vs LTV (can we afford to scale?). Each metric answers a different question. Confusing them leads to reporting that looks complete but obscures what's actually happening.

If you can only pick one, pick LTV:CAC ratio. It's the only metric that lets you answer the single most important question in marketing: can we keep doing this?