Marketing Mix Modeling (MMM) is a statistical technique that quantifies the actual contribution of each marketing channel -TV, paid search, email, social media, radio, display- on a company’s sales or conversions, without relying on cookies or individual user tracking. In 2026, driven by AI models, MMM is no longer exclusive to big brands and has become the measurement standard for any company that wants to know how much of its budget is really working. If your team is still making investment decisions based on the last click in GA4, you are measuring, at best, 40% of what actually happens. Why the MMM is back stronger than ever For years, digital marketing promised perfect attribution: knowing exactly which ad, at which time, converted which user. That promise was never quite fulfilled, and in 2026 it has been definitively broken for three converging reasons. The cookieless world is now an operational reality. Safari and iOS block cross-tracking from 2021. Firefox does the same. Chrome has drastically reduced the lifetime window of third-party cookies. The result: 40% to 70% of conversions come to GA4 tagged as direct traffic, with no attributable source. GA4 has structural attribution constraints. GA4’s data-driven model only works well with large volumes of data, undervalues awareness channels (TV, display, branded) and does not capture the lagged effect of advertising – a January branding campaign may influence a March purchase that GA4 will attribute to Google Ads. Privacy regulators have tightened the rules. The European RGPD, the Spanish AEPD and the consent standards of the platforms mean that more and more users are rejecting tracking. In sectors such as health, banking or legal, individual tracking is directly unfeasible. The MMM solves all three problems at once: it works with aggregated (not individual) data, it does not need cookies, and it captures effects that point tracking cannot see. How a modern MMM model works with AI A classic MMM used multiple linear regression to estimate the relationship between media spending and sales. The modern MMM with AI goes much further. The model receives as inputs the historical investment data in each channel (week by week or day by day), the sales or conversions of the business in the same period, and external control variables: seasonality, price, competitors, macroeconomic events. From there, the algorithm learns what part of sales is explained by each channel, what return per euro invested generates each one (incremental ROI), and what is the saturation curve of each medium (the point at which investing more does not generate more sales). The big new feature of the 2025-2026 models is the incorporation of Bayesian inference, which allows us to include prior knowledge of the business (e.g., “we know that TV has a 4-week carryover effect”) and to obtain confidence ranges rather than point figures. This makes the models much more honest and useful for decision making. Key concept – Carryover effect: the delayed effect of advertising. A display campaign launched today can continue to generate conversions for 2 to 6 weeks. The MMM captures this. GA4 does not. MMM vs. multi-touch attribution: the difference that matters Multi-touch allocation (GA4) Marketing Mix Modeling Data User level (cookies, sessions) Aggregate data (expense + sales) Privacy Consent and cookies required Does not use personal data Offline channels Do not capture TV, radio, OOH Includes all channels Delayed effect No Yes (carryover) Saturation No Yes (response curves) Speed Real time Weekly or monthly models Complexity Low-medium Medium-high (with AI tools: medium) The two approaches are complementary, not mutually exclusive. MMM tells you where the real ROI is at a strategic level; session tracking helps you optimize tactically within each channel. MMM tools being used by major brands in 2026 Until three years ago, building an MMM required a team of data scientists and months of work. Today there are four affordable alternatives: Google Meridian (open source, 2024). Google’s Bayesian model, available on GitHub. Requires knowledge of Python, but is free and transparent. Ideal for companies with in-house technical team or data agency. Meta Robyn (open source, R). The equivalent of Meta. Especially good if a relevant part of your investment is in the Meta ecosystem. Also free. Recast (SaaS). The most accessible option for non-technical marketing teams. Visual interface, automated modeling, dashboard outputs. Price starting at ~$2,000/month. Northbeam (SaaS). Highly oriented to ecommerce DTC. Combines MMM with multi-touch attribution and has native integrations with Shopify and major ad platforms. For medium-sized Spanish companies, the most practical route is to start with Meridian or Robyn with the support of a specialized agency, and move to a SaaS solution when the model is validated and the team has internalized the methodology. How to implement MMM in your company: the five actual steps 1. Collect two years of weekly historical data. Investment by channel (Google Ads, Meta, TV, email, estimated SEO), total sales or conversions, and control variables (average price, seasonality, competitor actions if any). 2. Define the dependent variable precisely. The model learns to explain what you tell it to explain. If you use total revenue, it will include all the noise. If you use new customer revenue, the result will be much more actionable. 3. Choose the model and set the Bayesian priors. Before the model learns from the data, you introduce what you already know: the time of effect of each channel, saturation constraints, seasonality periods. This step is the most critical and where business knowledge brings the most value. 4. Validate the model before making decisions. A good MMM should be able to predict historical weeks that it has not seen. If the prediction error is greater than 10-15%, the model is not ready. 5. Translates outputs into budget decisions. The MMM gives you the response curves for each channel. With them you can simulate scenarios: “what happens to my sales if I move €50,000 from TV to Google Ads?” That simulation is why big brands like Unilever, Nestlé or BBVA have been using MMM for decades. At Inprofit we integrate