ROI (Return on Investment)

How to calculate ROI

ROI is worked out with a simple formula: (revenue generated minus the cost of the investment) divided by the cost of the investment, multiplied by 100. If you invest 5,000 euros in a website that generates 20,000 euros of additional turnover, your ROI is 300%. In other words, every euro invested brought you 3 euros back.

The metric is universal, and it lets you compare how effective different marketing investments are: a website, a Google Ads campaign, an SEO strategy, social media posts. ROI turns subjective debate ("the site looks good") into objective data ("the site generates 15,000 euros a month").

Digital marketing ROI by channel

Average performance varies significantly from one channel to another. Email marketing delivers the best ROI, at 36 euros for every euro spent on average (DMA, 2025). SEO returns 5 to 12x over 12 months, with the advantage of traffic that lasts and keeps growing. Paid search, or SEA (Google Ads), produces an average return of 2 to 8x, depending on the sector and on how well the campaigns are optimised. Organic social media gives a return that is hard to measure directly, but it contributes to brand awareness.

For a website, ROI is measured by comparing the total cost (build plus maintenance plus hosting) with the revenue it generates (leads converted into customers, online sales, bookings). A 3,000 euro brochure site that generates 5 qualified leads a month, 2 of which become customers with an average order value of 2,000 euros, delivers an ROI of 1,500% in the first year.

How to improve your website's ROI

The conversion rate is the main lever. Doubling your conversion rate from 2% to 4% doubles your ROI without spending another penny on traffic. Optimising your CTAs, simplifying your forms, adding social proof and improving speed are the actions with the biggest impact.

Traffic quality is the second lever. A thousand qualified visitors, who are actively looking for your service, are worth more than 10,000 untargeted ones. SEO on commercial intent keywords and well targeted paid campaigns both improve traffic quality.

The average order value is the third lever. Upselling (offering a higher end product), cross selling (offering complementary products) and bundles all increase the value of each conversion.

Measuring ROI properly

Many companies fail to measure their digital ROI because they do not track conversions properly. Set up goals in Google Analytics 4, assign a value to each conversion (the value of a lead equals the lead to customer conversion rate multiplied by the average order value), and use UTM parameters to identify where each conversion came from.

Attribution is a major challenge: a customer might discover your business through Google, visit your site through a Meta ad, then convert through an email. Which channel generated the sale? Multi touch attribution models (Google Analytics 4, HubSpot) help answer that question.

ROI, ROAS and cost per lead: do not mix up the metrics

ROI is often confused with neighbouring metrics that measure something quite different. ROAS (Return on Ad Spend) only measures the return on advertising spend: it compares the turnover generated with the ad budget, without including the other costs (building the site, time spent, margin). A flattering ROAS can hide a mediocre ROI if your margins are thin.

Cost per lead (CPL) tells you what it costs to obtain a sales contact, and customer acquisition cost (CAC) what it costs to turn that contact into a paying customer. These indicators complement each other: ROI gives the overall picture of profitability, while ROAS, CPL and CAC shed light on each stage of the journey. For a small business, watching all three angles avoids cutting a profitable channel, or over investing in one that looks strong on the surface while it destroys margin.

Common mistakes when calculating ROI

- Forgetting the hidden costs: time spent, maintenance, commissions, tools, hosting. - Counting only the first purchase and ignoring customer lifetime value (a loyal customer is worth far more than their first order). - Attributing a sale to a single channel when the journey involved several touchpoints. - Measuring too early: SEO and content take several months before their real profitability shows. - Confusing turnover with margin: 20,000 euros of sales at a 10% margin is only 2,000 euros of actual profit.

Short term vs long term ROI

Paid search gives a return you can measure immediately, but it stops the moment you stop paying. SEO and content marketing give a return that grows over time: an optimised blog article costs 300 euros to produce and can bring in traffic for 3 to 5 years. It is this compounding effect that makes content marketing so powerful.

For a business owner or a small company, the ideal is to combine both horizons: paid search to get the first results quickly, SEO and content to build a lasting asset that keeps paying long after the initial investment. That combination is what maximises overall ROI across several years, rather than over a single month.

The ROI of a website for a tradesperson or a sole trader: a worked example

Take a concrete case that speaks to most business owners. A heating engineer invests 3,500 euros in a brochure site optimised for local SEO and enquiries. After three months, the site ranks for searches such as "heating engineer" followed by the name of his town, and receives around 400 visitors a month. With a conversion rate of 4% (16 quote requests a month) and a win rate of 30%, he lands around 5 new jobs a month, at an average value of 1,200 euros.

That comes to 6,000 euros of monthly turnover attributable to the site, or 72,000 euros over a year, for an initial investment of 3,500 euros plus around 50 euros a month in maintenance and hosting. Even counting only part of that turnover as genuinely down to the site, the return on investment comfortably exceeds 1,000% in the first year. This kind of calculation, adapted to your own margin and your own sector, turns the question "a website is expensive" into "how much will a website bring in?". That shift in perspective is precisely what separates a cost from an investment.

At ConvertiLab, we design every project with a clear ROI goal. We measure the results and keep optimising to get the most out of your investment, always keeping in mind the reality of a small business budget.