HHI Calculator: Calculate Market Concentration

An expert tool to calculate the Herfindahl-Hirschman Index (HHI) using up to 6 firm market shares.

Enter Market Shares

Input the market share for each firm as a percentage (e.g., enter 40 for 40%). You can analyze up to 6 firms.

Warning: The sum of market shares exceeds 100%.

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Herfindahl-Hirschman Index (HHI)

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What is the Herfindahl-Hirschman Index (HHI)?

The Herfindahl-Hirschman Index (HHI) is a widely accepted measure of market concentration. It is used by economists and antitrust regulators to assess the level of competition within an industry. A higher HHI indicates a more concentrated market, meaning fewer companies hold a larger percentage of the market share, which can approach a monopoly. Conversely, a lower HHI suggests a more competitive market with many firms, none of which has significant market power.

This metric is critical for authorities like the U.S. Department of Justice (DOJ) and the Federal Trade Commission (FTC) when they analyze the potential impact of mergers and acquisitions. If a merger is projected to significantly increase the HHI in an already concentrated market, it may be challenged on antitrust grounds.

HHI Formula and Explanation

The formula to calculate HHI is straightforward: you square the market share of each firm in the industry and then sum the resulting numbers. Market shares are typically expressed as whole numbers (e.g., 30% is entered as 30).

HHI = s₁² + s₂² + s₃² + … + sₙ²

The resulting HHI score can range from close to 0 (in a highly fragmented market with numerous small firms) to 10,000 (a pure monopoly where one firm has 100% market share).

Formula Variables

Variable	Meaning	Unit	Typical Range
HHI	Herfindahl-Hirschman Index	Points (Unitless)	0 – 10,000
sₙ	The market share of an individual firm ‘n’	Percentage (%)	0% – 100%
n	The total number of firms in the market	Count (Unitless)	1 to thousands

One of the key benefits of the HHI is that by squaring the market shares, it gives more weight to firms with larger shares, providing a more sensitive picture of market dominance than a simple concentration ratio.

Practical Examples of HHI Calculation

Example 1: A Highly Concentrated Market

Imagine a market for airplane manufacturing dominated by two major players.

• Firm 1 (Boeing-esque): 55% market share
• Firm 2 (Airbus-esque): 45% market share

The HHI calculation would be:

HHI = (55)² + (45)² = 3025 + 2025 = 5050

An HHI of 5050 is extremely high and indicates a very highly concentrated duopoly. You can learn more about how regulators view such markets with a merger simulation tool.

Example 2: A Competitive Market

Now consider the market for coffee shops in a large city, which is highly fragmented.

• Firm 1: 15% market share
• Firm 2: 12% market share
• Firm 3: 8% market share
• Firm 4: 7% market share
• Firm 5: 5% market share
• Firm 6: 4% market share
• (and many other smaller firms)

The HHI for just these top 6 firms would be:

HHI = (15)² + (12)² + (8)² + (7)² + (5)² + (4)² = 225 + 144 + 64 + 49 + 25 + 16 = 523

Even with many other smaller firms, the HHI is very low, indicating a highly competitive, unconcentrated market. This scenario is far from the concerns that trigger antitrust analysis.

How to Use This HHI Calculator

Using our tool to calculate HHI using 6 scenarios is simple and intuitive.

1. Enter Market Shares: For each of the up to six input fields, enter the market share of a firm in the industry. The value should be a percentage represented as a whole number (e.g., for 25% share, simply type “25”).
2. Leave Unused Fields Empty: If your market has fewer than six significant firms, you can leave the extra input fields empty or enter “0”. The calculator will automatically exclude them from the calculation.
3. Review Real-Time Results: As you type, the HHI score, number of firms, and total market share will update instantly.
4. Interpret the Score: The calculator provides an immediate interpretation based on the DOJ and FTC guidelines:
   • Below 1,500: Unconcentrated Market
   • 1,500 to 2,500: Moderately Concentrated Market
   • Above 2,500: Highly Concentrated Market
5. Analyze the Chart: The bar chart provides a quick visual reference for the market share distribution among the firms you entered, helping you understand the competitive landscape at a glance.

Key Factors That Affect HHI

Several factors can influence the HHI of an industry. Understanding them is crucial for a complete analysis.

1. Number of Firms:

The most direct factor. As the number of competitors decreases, the HHI score naturally increases, indicating higher concentration.

2. Distribution of Market Share:

An uneven distribution, where one or two firms hold a vast majority of the market share, will result in a much higher HHI than a market with many firms of similar size. A four-firm concentration ratio can also help measure this.

3. Barriers to Entry:

Industries with high barriers to entry (e.g., high capital costs, complex regulations, strong patents) tend to have fewer firms and thus a higher HHI.

4. Mergers and Acquisitions:

This is a primary focus of HHI analysis. A merger reduces the number of competing firms and consolidates market share, always leading to an increase in the HHI.

5. Market Definition:

How a market is defined (e.g., “soft drinks” vs. “cola soft drinks”) can dramatically change the HHI. A narrower definition will almost always result in a higher concentration score.

6. Government Regulation:

Regulations can act as barriers to entry, limiting the number of firms and thereby increasing market concentration. This is often a topic in merger guidelines.

Frequently Asked Questions (FAQ)

1. What is a “good” or “bad” HHI score?

There isn’t a universally “good” or “bad” score; it’s a measure of concentration. From a consumer and regulatory perspective, a lower score (below 1,500) is generally preferred as it indicates a competitive market. A score above 2,500 is considered highly concentrated and can attract regulatory scrutiny.

2. What happens if the market shares I enter don’t add up to 100%?

The HHI calculation is still valid for the firms you’ve included. However, it means your analysis is incomplete as it doesn’t account for the entire market. Our calculator will show a warning if the total exceeds 100% and displays the total share you’ve entered for transparency.

3. Can the HHI be over 10,000?

No. Since HHI is calculated from percentages, a monopoly with 100% market share results in an HHI of 100² = 10,000. It is the theoretical maximum.

4. How do regulators use the HHI for mergers?

Regulators calculate the HHI before and after a proposed merger. They are particularly concerned when a merger causes a significant jump in the HHI in a market that is already moderately or highly concentrated. An increase of over 100-200 points in a highly concentrated market is often a red flag.

5. Why does HHI give more weight to larger firms?

This is due to the squaring of each market share. A firm with 50% share contributes 2,500 points (50²), while five firms with 10% share each contribute only 500 points total (5 * 10²). This mathematical property helps emphasize the dominant role large firms play in a market.

6. What’s the difference between HHI and a concentration ratio (like CR4)?

A concentration ratio (e.g., CR4) simply adds the market shares of the top four firms. HHI is more sensitive because it squares the shares, better reflecting the disparity in size between firms. A market with four equal-sized firms can have the same CR4 as a market dominated by one giant firm and three small ones, but their HHI scores will be very different.

7. Is HHI the only metric used in antitrust analysis?

No. While HHI is a crucial screening tool, regulators consider many other factors, such as barriers to entry, the potential for innovation, and efficiencies gained from a merger. HHI is a starting point for a deeper antitrust analysis, not the final word.

8. Does this calculator handle more than 6 firms?

This specific tool is designed to easily calculate HHI using 6 scenarios for quick analysis. For a full market analysis, you would need to include the market share of all firms, though often the top 50 are used for practical purposes as smaller firms contribute very little to the final score.

Related Tools and Internal Resources

For a deeper understanding of market dynamics and economic analysis, explore these related resources: