Stop Chasing Growth: Why HHI Should Drive Your Next Market Move

Everyone tells you to chase the fastest-growing market. I'm going to tell you the opposite: the only growth number that matters is the one that won't get you blocked by the Department of Justice. You think you're being smart by targeting a hot segment with double-digit CAGR. You're actually setting yourself up for a regulatory nightmare if that segment is already concentrated. Here's how to think like a merger lawyer, not a growth hacker.

Your Growth Fantasy vs. the HHI Reality

Imagine you're the CEO of a mid-sized market research firm. Your board wants growth, and the data seems to point one way. The global insights industry is booming—it grew about 8.0% in 2023, with Asia Pacific leading at 9.5% (ESOMAR via Research World). You're tempted to acquire a smaller competitor in that region. But before you fire off a letter of intent, run the numbers through the Herfindahl-Hirschman Index (HHI). The HHI is the sum of the squares of the market shares of each firm in a market (US DOJ Antitrust Division). If your combined share would push the post-merger HHI above 1,800 and increase the index by more than 100 points, the 2023 Merger Guidelines presume the merger is unlawful (US DOJ Antitrust Division). That's not a suggestion; it's a presumption you'd have to rebut.

Now, you might say, “We're not that big.” But in a niche like, say, Kazakhstan—the fastest-growing market research market at almost 24% in 2023 (ESOMAR via Research World)—the market is small. A few players might already dominate. Your “small” acquisition could tip the HHI over the line. The same logic applies if you're in the US, which holds about 53% of the global market research market (Similarweb / Research and Markets). That's not just a dominance stat; it's a warning that US regulators are watching.

Know Your Market's Concentration Before You Commit

So how do you know if you're walking into a trap? Start with the HHI thresholds. A market is “moderately concentrated” between 1,000 and 1,800, and “highly concentrated” above 1,800 (US DOJ Antitrust Division). If you're in a highly concentrated market, any merger that increases the HHI by more than 100 points is presumed to substantially lessen competition (US DOJ Antitrust Division). That's the number you need to calculate before you even talk to a target.

Let's make it concrete. Suppose you're considering a merger in a market where the top four firms have shares of 30%, 25%, 20%, and 10%. The HHI is 900+625+400+100 = 2,025. That's already highly concentrated. If you're the fifth firm with 5% and you merge with the 10% firm, the new combined share is 15%, and the HHI rises by 2*5*10 = 100 points (since the sum of squares increases by 2*share1*share2). Post-merger HHI is 2,125, and the increase is exactly 100. You're right at the threshold—any higher and you're presumed unlawful. That's not a theoretical exercise; that's the kind of math you need to do.

This isn't just about mergers. Even organic growth can trigger scrutiny if you're in a concentrated market. The guidelines also presume that a merger creating a firm with more than 30% market share substantially lessens competition when the HHI increase exceeds 100 points (US DOJ Antitrust Division). So if you're approaching that share, think twice about any acquisition that pushes you over.

The Only Growth Strategy That Won't Backfire: Market Penetration

So what should you do instead of chasing a merger in a hot but concentrated market? The answer is boring but legal: market penetration. In the Duke CMO survey, market penetration—selling existing products to existing markets—was the most-used growth strategy in the past 12 months at 54.1% (Duke University CMO Survey). That's because it doesn't change the competitive structure of your market. You're not consolidating; you're just fighting harder for share. It's the default choice for a reason.

Yes, it's less glamorous than a headline-grabbing acquisition. But consider the alternative: a failed merger that gets blocked, costs millions in legal fees, and leaves you with nothing but a tarnished reputation. The HHI is your early warning system. If the numbers don't work, walk away. There are other markets to enter.

That said, if you do want to expand into a new market, be smart about it. Look at Asia Pacific, which is growing fast, but remember that its market research sector was revised upward from US$8.6 billion in 2022 to US$11.1 billion in 2023 (ESOMAR via Research World). That's a big pie, but it's also fragmented. Use HHI to find a niche that's not already dominated by a few players. For instance, Vietnam grew at 17.2% and India at 14.8% (ESOMAR via Research World). Those markets are less likely to be concentrated, so you have room to enter without triggering regulatory alarm.

How to Read the Market Like a Regulator

You don't need to be a DOJ economist to use this. You just need to know the two numbers: the post-merger HHI and the increase. If the post-merger HHI is above 1,800 and the increase is over 100, you're in the danger zone. That's it. You can compute this yourself with publicly available market share data.

But don't just look at your own market. Look at the broader industry trends. The global insights industry is shifting: in 2023, the market research sector accounted for about US$54 billion, the research software sector US$56 billion, and the reporting sector US$33 billion (ESOMAR via Research World). The software sector grew 12.4%, while the mature market research sector grew only 4.6% (ESOMAR via Research World). If you're in software, you might be tempted to consolidate. But that sector might be even more concentrated. Run the HHI before you make a move.

The point is, growth for growth's sake is a trap. The HHI is the lens through which you should view every strategic move. It's not about being timid; it's about being smart. You want to grow, but you want to grow in a way that doesn't invite a lawsuit.

Quick tip: Before any acquisition, calculate the HHI of the relevant market. If it's above 1,800, assume the merger is dead on arrival unless you have a compelling efficiency argument.

The Takeaway: Growth Is a Legal Strategy

You can't divorce market trends from antitrust law. The fastest-growing market is often the most concentrated, and the most concentrated markets are the most dangerous for mergers. So stop chasing CAGR and start calculating HHI. The numbers are clear: if the post-merger HHI is over 1,800 and the increase is over 100, the DOJ will presume your merger is illegal (US DOJ Antitrust Division). That's not a hypothetical; that's the rule. Use it to filter your targets. If a market is already concentrated, your growth strategy should be penetration, not acquisition. That's not just legal; it's smart.

Sources

• Similarweb / Research and Markets - https://www.similarweb.com/blog/research/market-research/market-research-stats/
• ESOMAR via Research World - https://researchworld.com/articles/drivers-of-our-142bn-insights-industry
• ESOMAR via Research World (Asia Pacific) - https://researchworld.com/articles/the-remarkable-ascent-of-asia-pacific-in-global-insights
• Duke University CMO Survey - https://cmosurvey-new.fuqua.duke.edu/how-does-your-company-grow/
• US DOJ Antitrust Division - https://www.justice.gov/atr/herfindahl-hirschman-index