HHI Calculator (Herfindahl-Hirschman Index Calculator)

The HHI is calculated by taking the market share percentage of every firm competing in a specific market, squaring each individual percentage, and then summing those squares together. Mathematically, the formula is expressed as HHI = s1^2 + s2^2 + s3^2 + ... + sn^2, where 's' represents the percentage market share of each firm. Standard regulatory frameworks, such as those used by the U.S. Department of Justice, categorize the resulting index into three distinct buckets: an HHI below 1,500 indicates a competitive marketplace; an HHI between 1,500 and 2,500 points to moderate concentration; and an HHI exceeding 2,500 signals high market concentration.

Imagine analyzing a localized software market featuring four competing technology firms with varying market dominance. Firm A holds 40 percent of the market, Firm B holds 30 percent, Firm C holds 20 percent, and Firm D holds 10 percent. To calculate the HHI, we square each firm's whole-number market share: 40 squared equals 1,600; 30 squared equals 900; 20 squared equals 400; and 10 squared equals 100. Summing these squared values together (1600 + 900 + 400 + 100) results in a total HHI score of 3,000. Because this score exceeds the 2,500 threshold, antitrust authorities would classify this specific industry as highly concentrated.

When inputting data into the calculator, ensure that your market share percentages account for the entire relevant market rather than just a narrow niche, as skewed definitions can artificially inflate or deflate concentration scores. Additionally, always verify that your total market share percentages sum up to exactly 100 percent to maintain analytical accuracy. Finally, use the HHI score as an initial screening tool rather than a definitive legal conclusion, as regulators also weigh entry barriers and innovation dynamics.