HHI Calculator
An essential tool for measuring industry competition and market concentration.
Market Share Distribution
What is the Herfindahl-Hirschman Index (HHI)?
The Herfindahl-Hirschman Index (HHI) is a widely accepted measure of market concentration. It illustrates the size of companies in relation to their industry and indicates the level of competition among them. Named after economists Orris C. Herfindahl and Albert O. Hirschman, the HHI is calculated by squaring the market share of each firm competing in a market and then summing the resulting numbers. This powerful metric is extensively used by antitrust authorities, including the U.S. Department of Justice (DOJ) and the Federal Trade Commission (FTC), to evaluate the potential impact of mergers and acquisitions on an industry’s competitive landscape.
A higher HHI score generally indicates a decrease in competition and an increase in market power, while a lower score suggests a more competitive market with numerous participants. The scale ranges from close to zero (perfect competition) to 10,000 (a pure monopoly). Our hhi calculator provides a quick and accurate way to compute this index and understand market dynamics.
HHI Calculator Formula and Explanation
The formula for the Herfindahl-Hirschman Index is straightforward yet powerful. It gives more weight to firms with larger market shares, making it a more sensitive measure of market power than simple concentration ratios.
The formula is:
HHI = s₁² + s₂² + s₃² + … + sn²
Where each variable represents a specific component of the market structure:
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| HHI | Herfindahl-Hirschman Index | Points (unitless) | 0 to 10,000 |
| sᵢ | The market share of an individual firm ‘i’ | Percentage (%) | 0% to 100% |
| n | The total number of firms in the market | Count (unitless) | 1 to ∞ |
Practical Examples
Example 1: A Highly Concentrated Market
Consider a hypothetical tech hardware market dominated by a few major players.
- Firm A (Input): 50% market share
- Firm B (Input): 25% market share
- Firm C (Input): 15% market share
- Firm D (Input): 10% market share
Using the hhi calculator formula:
HHI = 50² + 25² + 15² + 10² = 2500 + 625 + 225 + 100 = 3450
This result indicates a highly concentrated market, as it is well above the 2,500-point threshold. For more details on market power, see our article on concentration analysis.
Example 2: An Unconcentrated Market
Now, imagine a local restaurant market with many small competitors.
- 10 Firms (Input): Each holds a 10% market share
The calculation would be:
HHI = 10 * (10²) = 10 * 100 = 1000
This HHI score is below 1,500, signifying a competitive, unconcentrated industry where no single firm has significant market power.
How to Use This HHI Calculator
Our tool simplifies the process of measuring market concentration. Follow these steps for an accurate analysis:
- Enter Market Shares: For each firm in the market, enter its market share as a percentage (e.g., enter 40 for 40%). By default, four input fields are provided.
- Add More Firms: If your market has more than four competitors, click the “Add Firm” button to generate additional input fields.
- Calculate: Once all market shares are entered, click the “Calculate HHI” button.
- Interpret Results: The calculator will display the total HHI score, an interpretation of the market concentration level (Unconcentrated, Moderately Concentrated, or Highly Concentrated), and a table with intermediate values. The results are based on guidelines from the U.S. Department of Justice.
- Analyze the Chart: A dynamic bar chart will visualize the market share distribution, making it easy to see the relative size of each firm.
Understanding these results is crucial for strategic decisions, a topic explored in our guide to market structure analysis.
Key Factors That Affect HHI
Several factors can influence the HHI score and the overall market concentration:
- Number of Firms: The most direct factor. Fewer firms in a market will almost always lead to a higher HHI.
- Distribution of Market Shares: A market with firms of unequal sizes will have a higher HHI than a market with the same number of firms of equal size. The HHI gives more weight to larger firms.
- Barriers to Entry: High barriers to entry (e.g., high startup costs, regulatory hurdles) can limit the number of new competitors, keeping concentration high.
- Mergers and Acquisitions: When firms merge, the number of competitors decreases, and the market share of the new entity increases, which directly raises the HHI. Antitrust agencies use the hhi calculator to scrutinize these changes.
- Product Differentiation: Industries with highly differentiated products may allow many firms to coexist in niche segments, potentially leading to lower concentration.
- Government Regulation: Policies can either encourage competition or, in some cases (like with patents or exclusive licenses), create legally-protected monopolies or oligopolies.
For a deeper dive, consider reading about competitive strategy.
Frequently Asked Questions (FAQ)
What is a good HHI score?
There isn’t a “good” or “bad” score; it’s a measure of concentration. According to the U.S. Department of Justice, markets with an HHI below 1,500 are considered unconcentrated (competitive), between 1,500 and 2,500 are moderately concentrated, and above 2,500 are highly concentrated.
Why do you square the market shares?
Squaring the market shares gives greater weight to firms with larger shares. This makes the HHI more sensitive to the influence of dominant firms than a simple concentration ratio, which just sums the shares of the top firms.
Can the HHI be over 10,000?
No. Since market shares are percentages that sum to 100, the theoretical maximum HHI is 10,000. This occurs in a monopoly where one firm has 100% of the market (100² = 10,000).
What is the lowest possible HHI?
The HHI approaches zero as the number of firms becomes very large and each firm’s market share becomes very small, representing a state of perfect competition.
How do antitrust agencies use the HHI?
Regulators like the DOJ and FTC use the HHI to screen mergers. A merger that significantly increases the HHI in an already concentrated market will likely trigger further investigation for potential anti-competitive effects. You can learn more about this in our article on merger analysis.
What are the limitations of the HHI?
The HHI’s primary limitation is its simplicity. It requires a proper definition of the “market,” which can be complex. It also doesn’t account for factors like foreign competition, potential new entrants, or the specific nature of competition in an industry.
How is HHI different from a concentration ratio (like CR4)?
A concentration ratio (e.g., CR4 sums the market share of the top four firms) is simpler but less informative. The HHI includes all firms and gives more weight to larger ones, providing a more robust picture of the competitive landscape.
Do I enter percentages or decimals in the hhi calculator?
You should enter the market shares as whole numbers. For example, a 25% market share should be entered as “25”, not “0.25”. The calculator handles the squaring automatically.