📊 Market Share Calculator
A market share calculator that also computes the Herfindahl-Hirschman Index, using the current 2023 DOJ/FTC Merger Guidelines concentration bands.
What Market Share Calculator Does
Market share is one division: your revenue or unit sales over the total for the market you have defined. The arithmetic is trivial. The part that actually determines whether the number means anything is how "the market" gets defined — by geography, by product category, by customer segment — because the same company can honestly report very different shares depending on where that line is drawn.
A single share percentage also hides how concentrated the market actually is. A company with 25% share in a market of four equal competitors is in a very different competitive position than a company with 25% share against one dominant player holding 60%. This tool also computes the Herfindahl-Hirschman Index (HHI), the standard measure of market concentration used by US antitrust regulators, precisely because it captures that difference and a bare share percentage does not.
The HHI thresholds published on many calculator sites and in older textbooks are stale. The Department of Justice and FTC revised their concentration bands in the 2023 Merger Guidelines, and this tool uses the current bands — verified directly against the DOJ's own page rather than the older, still-widely-repeated numbers.
How to Use Market Share Calculator
- Enter your company's revenue (or units sold) and each competitor's
- Add an "everyone else" row if you are not listing every competitor, so the total reflects the true market
- Read each entry's market share percentage and the market's overall HHI concentration score
Formula Used by Market Share Calculator
Market share
Market share (%) = (company revenue or units ÷ total market revenue or units) × 100
Worked example
Your company: $2.5M. Competitor A: $4M. Competitor B: $3M. Everyone else: $2.5M.
- Total market: 2.5M + 4M + 3M + 2.5M = $12M
- Your share: 2.5M ÷ 12M × 100
Result: 20.83% — with Competitor A at 33.33%, Competitor B at 25.00%, and everyone else at 20.83%.
Herfindahl-Hirschman Index
HHI = Σ (each firm's market share, as a whole number 0–100)²
- Range
- Approaches 0 with many equal-sized competitors; reaches exactly 10,000 for a single-firm monopoly
Worked example
The Department of Justice's own published example: four firms with shares of 30%, 30%, 20% and 20%.
- 30² + 30² + 20² + 20²
- = 900 + 900 + 400 + 400
Result: 2,600 — the exact figure the DOJ's Antitrust Division cites, confirming this tool's formula matches the regulator's own arithmetic.
HHI concentration bands — current (2023 Merger Guidelines)
Verified against justice.gov/atr/herfindahl-hirschman-index, updated January 17, 2024. Supersedes the older 1,500/2,500 bands still repeated on many calculator sites.
| HHI range | Classification |
|---|---|
| Below 1,000 | Unconcentrated |
| 1,000–1,800 | Moderately concentrated |
| Above 1,800 | Highly concentrated |
Source: US Department of Justice — Antitrust Division, Herfindahl-Hirschman Index
Same top-firm share, very different concentration
Illustrates why HHI is not just "the biggest company's share" — the number of remaining competitors and how evenly they split the rest matters just as much.
| Scenario | Shares | HHI | Classification |
|---|---|---|---|
| One dominant firm | 40%, 20%, 20%, 20% | 2,800 | Highly concentrated |
| Same leader, more rivals | 40%, 15%, 15%, 15%, 15% | 2,500 | Highly concentrated |
| Four roughly equal firms | 25%, 25%, 25%, 25% | 2,500 | Highly concentrated |
| Ten equal firms | 10% each × 10 | 1,000 | Borderline moderately concentrated |
How to Read Your Result
Define the market before trusting the percentage
A 20% share of "the global market" and a 20% share of "the regional market for one product line" are not comparable numbers even though they look identical. Whoever is comparing market share figures across companies or reports needs to confirm both are using the same market definition, or the comparison is meaningless.
A missing "everyone else" bucket inflates every listed share
If a market genuinely has a long tail of small competitors and only the top few are entered, the total is understated and every listed company's share — and the resulting HHI — comes out too high. Add a catch-all row for the remainder whenever the listed competitors do not represent the whole market.
HHI rewards evenness, not just fewer competitors
The comparison table above shows four equal 25% competitors producing the same 2,500 HHI as a market led by one 40% firm against three 15%-ish rivals — concentration is about the size distribution, not simply the competitor count. A market can have many players and still be highly concentrated if one dominates.
Limitations & Accuracy Notes
- Market share and HHI are only as accurate as the total-market figure entered. Neither this tool nor any calculator can verify that the total reflects the real market — that data has to come from industry research, not from the numbers typed in.
- This computes a snapshot at one point in time. Market share trends (gaining or losing share period over period) require repeating the calculation with each period's figures.
- HHI concentration bands are the standard used in US antitrust merger review; other countries' competition regulators use similar but not always identical thresholds.
- Revenue-based and unit-based market share can disagree when companies price differently — this tool computes whichever figure (revenue or units) is entered, and does not convert between the two.
Frequently Asked Questions
What is the market share formula?
What does 20% market share mean?
What is the Herfindahl-Hirschman Index (HHI)?
What HHI counts as a "concentrated" market?
Does adding a small "everyone else" bucket change the result much?
Is my data stored?
References & Further Reading
- US Department of Justice — Antitrust Division, Herfindahl-Hirschman Index — Source of the HHI formula, the DOJ's own 30/30/20/20 = 2,600 worked example used above, and the current 1,000/1,800 concentration bands from the 2023 Merger Guidelines