Marketing ROI answers one question: for every unit of currency you put into a campaign, how much revenue came back? The basic formula is simple. Take the revenue attributable to the campaign, subtract the campaign cost, then divide by that cost. A result of 3:1 means each dollar spent returned three.

The formula is easy. Getting honest numbers into it is the hard part.

Count the full cost

Ad spend is only the visible slice. A realistic cost figure also includes agency fees, creative production, software subscriptions, and the hours your own team spent on the work. Leaving those out inflates ROI and leads to bad budget decisions later. Track cost per channel, not just per campaign, so you can compare like with like.

Attribution decides everything

Revenue rarely comes from a single touch. A buyer might find you through search, return via a newsletter, and convert after a retargeting ad. Before you report ROI, decide on an attribution model and apply it consistently:

• Last-touch credits the final interaction. Simple, but it undervalues awareness work.
• First-touch credits discovery. Useful for judging top-of-funnel channels.
• Multi-touch spreads credit across the journey. Harder to set up, closer to reality.

No model is perfect. Consistency matters more than precision, because trends over time are what you act on.

A mediocre campaign measured well will teach you more than a great campaign measured badly.

Give campaigns time to mature

Judging a campaign in its first week punishes anything with a long sales cycle. Content and SEO can take months to pay back, while paid search can show returns in days. Set an evaluation window that matches how your customers actually buy, and note it in every report so results are read in context.

Move from measuring to deciding

ROI is a steering tool, not a scoreboard. Review it on a fixed cadence, shift budget toward the channels that hold up after full costs and fair attribution, and cut what consistently underperforms. Small, regular reallocations beat one dramatic annual overhaul, and they keep the whole team focused on outcomes rather than activity.