FTC & DOJ HHI Merger Concentration Calculator

Understanding HHI & Market Concentration under the 2023 Merger Guidelines

In antitrust law, measuring market concentration is the foundational starting point for any analysis regarding whether a proposed merger or acquisition will face regulatory hurdles. Historically, the Federal Trade Commission (FTC) and the Department of Justice (DOJ) Antitrust Division utilized structural metrics to classify markets. In late December 2023, the federal agencies finalized a sweeping set of modernized Horizontal and Vertical Merger Guidelines that significantly lowered the bar for when a transaction is legally presumed to harm competition.

What is the Herfindahl-Hirschman Index (HHI)?

The Herfindahl-Hirschman Index (HHI) is calculated by squaring the percentage market share of each firm competing in a defined market, and then summing those squares. Market shares are represented as whole numbers (e.g., a 20% share is squared as 20 * 20 = 400). If a market is a pure monopoly, the HHI is 10,000 (100^2 = 10,000).

By squaring the shares, the HHI naturally gives significantly greater weight to firms with larger market shares. This reflects the economic reality that highly dominant players exert disproportionately large competitive influence compared to smaller, fragmented players.

The Drastic Shifts in the 2023 Merger Guidelines

The 2023 Guidelines represent a dramatic departure from the 2010 standards, reverting in many ways to a stricter structural presumption standard last seen in the 1980s. Key changes include:

• Lowering the Highly Concentrated Threshold: Under the 2010 Guidelines, a market was only considered "highly concentrated" if the post-merger HHI exceeded 2,500. The 2023 standards lowered this threshold back to 1,800.
• Tightening the Presumption Delta (ΔHHI): A merger in a highly concentrated market is presumed anticompetitive if the change in concentration (ΔHHI) is greater than 100. (The 2010 guidelines required a delta of 200).
• Introducing the 30% Dominant Firm Rule: Perhaps the most significant change is the creation of a standalone presumption. If a merged firm will have a market share of greater than 30% and the ΔHHI is greater than 100, the transaction triggers a presumption of illegality, even if the total post-merger HHI of the market remains low.

How to Rebut a Structural Presumption

A regulatory presumption is not an absolute barrier; rather, it shifts the burden of proof to the merging parties to show that structural concentration will not translate into anticompetitive outcomes. Parties typically rely on the following economic and legal defenses:

1. Low Entry Barriers (Ease of Expansion): Demonstrating that new competitors can easily enter the market, or that existing small competitors have significant unused capacity that they could rapidly scale up if the combined firm raised prices.
2. Countervailing Buyer Power:Proving that the target market consists of large, highly sophisticated enterprise purchasers (often called "Power Buyers") who can easily play suppliers off against each other or vertically integrate to protect themselves.
3. Verifiable Efficiencies: Presenting detailed econometric evidence of transaction-specific, non-dilutive synergies that will significantly reduce marginal costs, which will ultimately be passed down to the end consumer.
4. The Failing Firm Doctrine: A highly strict defense requiring proof that the target company is in imminent danger of financial failure, cannot successfully reorganize under Chapter 11 bankruptcy, and has made extensive, unsuccessful good-faith efforts to secure a less anticompetitive buyer.