One of the most predictive metrics in marketing is one that almost no one outside academia talks about.
It is called Share of Voice vs. Share of Market. When SOV exceeds SOM, brands grow. When SOV falls below SOM, brands shrink. It is almost that linear.
I want to walk through what this means, where the research comes from, and why every CFO should understand the math before they make their next decision about marketing budget.
Definitions
Two terms. Both straightforward.
Share of Market (SOM) is the percentage of total category sales your brand owns. If your category did $1 billion in sales last year and your brand did $100 million, your SOM is 10 percent.
Share of Voice (SOV) is the percentage of total category advertising spend you represent. If the category collectively spent $200 million on advertising last year and your brand spent $24 million, your SOV is 12 percent.
The relationship between these two numbers is the predictive variable.
The relationship
When your SOV exceeds your SOM, your brand grows.
When your SOV falls below your SOM, your brand shrinks.
The mechanism is straightforward. Marketing builds mental availability — the likelihood that a buyer will think of your brand when they enter the buying moment. Mental availability accrues over time and decays without continued investment. Brands that invest disproportionately to their current size build mental availability faster than the category leader can defend it. Brands that underinvest relative to their size lose mental availability to competitors who are investing more aggressively.
Marketing is a long game played by people on short contracts. The math of share of voice is the math of the long game.
Where the research comes from
The SOV/SOM relationship has been studied repeatedly across decades. The foundational work comes from John Philip Jones in the 1990s. The most cited modern treatment is from Les Binet and Peter Field, whose research with the Institute of Practitioners in Advertising in the UK has replicated the finding across hundreds of brands and dozens of categories.
The Binet and Field analysis suggests that the ratio between SOV and SOM is one of the most reliable predictors of future market share growth or decline in mature categories. The effect is strongest in categories with stable category-level demand, where competitive position is largely a function of mental availability rather than product superiority.
The relationship has been replicated in B2B, B2C, durables, consumer packaged goods, and services. It holds across geographies. It holds across decades. It is one of the most validated findings in marketing science — and one of the least applied in marketing practice.
The math, with a worked example
Let me make this concrete with two scenarios.
Scenario A. Your brand has 10 percent market share. Your category spends a combined $500 million on advertising annually. You spend $60 million — which is 12 percent of category advertising. Your SOV (12 percent) exceeds your SOM (10 percent) by 2 percentage points. Based on the research, your brand should be expected to gain approximately 0.5 to 1.0 points of market share over the next 12 to 24 months, assuming everything else holds constant.
Scenario B. Same brand. Same 10 percent market share. Your category still spends $500 million on advertising. But due to a CFO decision to cut marketing budget by 30 percent, you now spend $42 million — which is 8.4 percent of category advertising. Your SOV (8.4 percent) is below your SOM (10 percent) by 1.6 percentage points. The same research suggests your brand will lose 0.5 to 1.0 points of market share over the next 12 to 24 months.
The two scenarios produce dramatically different futures from a single budget decision. The decision feels like it is about this year's expenses. It is actually about next year's market share.
Why CFOs cut marketing during downturns
This is where the math becomes important.
When revenue dips, every CFO looks for cost reductions that protect margin. Marketing is one of the easiest line items to cut because it is treated as discretionary. The salaries are real but not committed. The advertising spend is variable. The agency relationships have contractual flexibility.
So the CFO cuts marketing. The dashboard looks better in the next quarter. Margin is protected. The CEO is happy. The board is happy.
18 months later, the brand has lost 1 to 2 points of market share. The lost share translates into millions of dollars of lost revenue per year, compounding for years afterward. The cost of the original budget cut, properly accounted for, exceeds the savings by a factor of 3 to 10.
The CFO does not see this. The dashboard the CFO is looking at does not measure mental availability, share of voice, or future market share trajectory. The dashboard measures only what is immediately visible. So the cost of the decision shows up far away from the decision itself, and the cause-and-effect relationship is invisible inside the company's reporting systems.
How small brands can use this strategically
Here is the asymmetric opportunity for small brands.
If you have 2 percent market share and you want to grow to 5 percent, you must spend like a 5 percent brand long before you become one. Spending like a 2 percent brand will keep you at 2 percent. The math is unforgiving.
Most small brands do the opposite. They spend below their current market share because they cannot afford to spend more, and they wonder why their growth has stalled. The reason their growth has stalled is that their SOV has been below their SOM for years.
The strategic implication is that growth-oriented small brands need to be willing to absorb short-term financial pressure to fund disproportionate marketing investment. This is uncomfortable. It is also the only path. Brands that try to grow while underspending on marketing typically don't.
How dominant brands defend their position
On the other side of the market, category leaders defend their position by maintaining SOV at or above SOM even when growth slows.
The temptation for category leaders is to milk their position by reducing marketing investment in mature categories. The category isn't growing. The leader's share isn't growing. Why keep spending?
The answer is that the lack of SOV investment creates the opening for challengers to gain ground. The challenger that invests aggressively while the leader coasts is the challenger that takes share over the next decade. Category leaders that maintain disciplined SOV investment — even during periods of slow growth — defend their position. Category leaders that don't, lose it slowly until they don't.
A practical exercise
Three steps to estimate your own category's SOV/SOM relationship.
• Step one — estimate total category advertising spend. Industry reports from groups like eMarketer, Statista, or Kantar publish annual estimates of advertising spend by category. Public companies disclose marketing spend in annual reports. Use these sources to triangulate the category total.
• Step two — calculate your own marketing investment as a percentage of that category total. This is your current SOV. Include media spend, content production, agency fees, and any major marketing payroll if you want a full picture.
• Step three — compare to your current market share. If your SOV exceeds your SOM, you are positioned to grow. If your SOV is below your SOM, you are positioned to shrink. Plan accordingly.
This is not a perfect calculation. Category boundaries are fuzzy. Marketing spend reporting is inconsistent. You will be working with estimates. The estimates are still more useful than no calculation at all.
Why this metric matters now
Three reasons SOV/SOM has become more important, not less, in the current marketing environment.
First — attribution is getting harder. The death of third-party cookies, the rise of privacy regulation, and the shift to walled-garden ecosystems have all made bottom-of-funnel attribution less reliable. Brands that overweighted attribution have less reliable data than they used to. SOV/SOM is a measurement framework that works regardless of attribution availability.
Second — paid media costs are rising. The cost per impression in most categories has increased significantly over the past five years. This means that maintaining SOV requires growing absolute marketing spend just to stay in place. Brands that don't realize this are quietly losing SOV without realizing it.
Third — competitor activity is more aggressive. Categories that were once dominated by a handful of incumbents are now contested by direct-to-consumer challengers, private equity-backed roll-ups, and platform-enabled new entrants. The challenger SOV is rising in nearly every category. Incumbents that do not respond lose share.
