HHI Calculator — Herfindahl-Hirschman Index
The HHI measures how concentrated a market is by squaring and summing each firm's market share. Enter the percentage share of each firm in the market (up to 10 firms) to get the index, the DOJ classification and the top-4 concentration ratio.
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Moderately concentrated
- 1
Square each market share
30² + 25² + 20² + 15² + 10²Squaring amplifies large players — a 50% share contributes 2,500 vs 100 for a 10% share. - 2
HHI (sum of squared shares)
900 + 625 + 400 + 225 + 100 = 2,250
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HHI = sum of squared market shares (each in %). A score below 1,500 is unconcentrated; 1,500–2,500 is moderately concentrated; above 2,500 is highly concentrated (DOJ thresholds). Enter each firm's percentage share — the tool squares and sums them, and also shows the top-4 concentration ratio (CR4).
Formula
How this is calculated
The Herfindahl-Hirschman Index was independently developed by Orris Herfindahl and Albert Hirschman in the 1940s–50s and is now the standard tool regulators use to screen mergers for anti-competitive effects. It is computed by squaring the market share of each firm — expressed as a plain percentage, not a decimal — and summing those squares across all firms in the market. Squaring amplifies the contribution of large players: a single firm with 50% contributes 2,500 points while ten equal firms at 10% each sum to only 1,000 points.
The US Department of Justice (DOJ) and Federal Trade Commission (FTC) publish three zones for HHI: markets below 1,500 are classified as unconcentrated and are unlikely to attract antitrust scrutiny; 1,500 to 2,500 are moderately concentrated; above 2,500 are highly concentrated. A merger that would raise the HHI by more than 200 points in a highly concentrated market triggers a presumption of competitive harm under the 2023 Merger Guidelines.
The normalised HHI divides the raw index by 10,000 to give a 0–1 scale; a monopoly scores exactly 1. The concentration ratio CR4 is the combined market share of the four largest firms — a simpler but less sensitive indicator of market power. Both metrics are approximate: they assume market shares are measured correctly and that market boundaries are well-defined, which can be contested in practice.
Mistoqsijiet frekwenti
The DOJ classifies markets with HHI above 2,500 as highly concentrated. A pure monopoly (one firm with 100%) scores 10,000 — the maximum possible. Markets below 1,500 are considered competitive and generally do not raise antitrust concerns.
Ideally yes, since HHI assumes you have covered the whole market. If you enter shares for only the top firms and the total is below 100%, the HHI will be understated. You can add a residual "Other" share to account for the fringe.
The DOJ/FTC use the post-merger HHI and the increase in HHI (delta) as screening filters. Under the 2023 guidelines, a post-merger HHI above 1,800 combined with a delta above 100 raises a preliminary competitive concern, triggering closer review.
Magħruf ukoll bħala
TG we-Calculate Editorial Team. (2026). HHI Calculator — Herfindahl-Hirschman Index [Online calculator]. TG we-Calculate. https://we-calculate.com/mt/calculator/hhi-calculator
TG we-Calculate Editorial Team. "HHI Calculator — Herfindahl-Hirschman Index." TG we-Calculate. 2026. https://we-calculate.com/mt/calculator/hhi-calculator.
TG we-Calculate Editorial Team, "HHI Calculator — Herfindahl-Hirschman Index," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/mt/calculator/hhi-calculator
@misc{wecalculate_hhi_calculator, title = {HHI Calculator — Herfindahl-Hirschman Index}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/mt/calculator/hhi-calculator}}, year = {2026}, note = {TG we-Calculate} }
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