How to Calculate ROAS and ROI by Combining Ad Data With Margin Data
ROAS (Return on Ad Spend) tells you how much revenue each pound of advertising brings in. ROI (Return on Investment) tells you how much profit you made relative to what you spent. To know which campaigns are genuinely profitable, you need both, and that means combining your ad platform data with your financial margin data.
ROAS and ROI: what's the difference?
ROAS = revenue from ads ÷ ad spend
If you spend £1,000 and the ads generate £4,000 in sales, your ROAS is 4.0 (or 400%).
ROI = (profit − cost) ÷ cost
ROI looks at profit rather than revenue, so it reflects what each campaign really earned after the cost of the goods or services sold and the ad spend itself.
ROAS is quick to calculate because ad platforms report it directly. Its weakness is that it ignores your margins, which is where many businesses go wrong.
Why ROAS alone can mislead you
A campaign can have an impressive ROAS and still lose money. Consider the following example:
| |
Campaign A |
Campaign B |
|---|---|---|
| Ad spend |
£10,000 |
£5,000 |
| Revenue generated |
£40,000 |
£15,000 |
| ROAS |
4.0 |
3.0 |
| Gross margin on sales |
20% |
50% |
| Gross profit |
£8,000 |
£7,500 |
| Profit after ad spend |
−£2,000 |
+£2,500 |
| ROI |
−20% |
+50% |
On ROAS alone, Campaign A looks better. Once margin is included, it loses money while Campaign B turns a profit. Without margin data, you could end up scaling the wrong campaign.
What's your break-even ROAS?
You can work out the minimum ROAS a campaign needs just to cover its costs:
Break-even ROAS = 1 ÷ gross margin
At a 20% margin, break-even ROAS is 5.0. At a 50% margin, it's 2.0 Anything below that line loses money, regardless of how healthy the headline number looks.
What data do you need?
To build the full picture, you'll typically pull together:
Ad data: spend, clicks, and attributed sales by campaign, from your ad platforms.
Sales data: orders and revenue from your e-commerce platform or sales system.
Margin data: cost of goods or delivery costs, from your accounting or finance system.
The challenge is that these live in different places and use different formats, so they need cleaning and matching before they can be compared.
How to combine them
Decide the question. For example, "Which campaigns make a profit after costs?"
Identify the sources. List where ad, sales, and margin data are held.
Match the data. Link campaigns to the products or orders they generated, using consistent identifiers.
Apply margins. Calculate profit per campaign, not just revenue.
Automate it. Build a report that refreshes on a schedule so you can see profitability as campaigns run, not weeks later.
Common pitfalls
Trusting platform-reported revenue. Ad platforms can over-attribute sales, so cross-check against your own sales records.
Using one blended margin. Different products have different margins, which changes which campaigns pay off.
Ignoring other costs. Agency fees, creative costs, and discounts all affect true ROI.
Looking at too short a window. Some customers buy again later, so consider lifetime value where relevant.
How Clear Data Consulting can help
Clear Data Consulting pulls financial margin data and ad traffic data together to give a full picture of which campaigns generate the most profit. Reporting applications are built at a daily rate of £500, starting by documenting your objectives. A Data and Reporting Health Check is a good first step if you're not sure what data you have or how reliable it is.
Frequently asked questions
What is ROAS?
Return on Ad Spend: the revenue generated for every pound spent on advertising.
What's the difference between ROAS and ROI?
ROAS measures revenue against ad spend. ROI measures profit against cost, so it accounts for margins.
What is a good ROAS?
It depends on your margins. Your break-even ROAS is 1 divided by your gross margin, so a good ROAS is comfortably above that.
Why does my ad platform's ROAS differ from my own figures?
Platforms attribute sales using their own rules, which can differ from your sales records. Reconciling the two is part of good reporting.
Can this be automated?
Yes. Once the data sources are connected and the definitions agreed, profitability reports can refresh hourly, daily, or weekly.
Request a free consultation to talk about getting a clear view of your campaign profitability.
Written by Matthew Bryant, Principal Consultant at Clear Data Consulting, a data and analytics leader with over 15 years of experience across retail, manufacturing, and service industries.