π Gini Coefficient Calculator
From quintile shares to a 0-to-1 inequality score.
Gini coefficient (0 = equal, 1 = max inequality)
Estimates for planning only, not financial advice.
The Gini coefficient compresses a whole income distribution into one number between 0 and 1: 0 is perfect equality, 1 is one person holding everything. Feed in the five quintile shares of US-style household income, 3, 8, 14, 23, and 52 percent, and the Gini comes out around 0.452, squarely in high-inequality territory by rich-country standards.
How to Use This Calculator
Enter the share of total income going to each fifth of households, lowest to highest. Shares do not need to sum to exactly 100; the calculator normalizes them.
Enter the five quintile income shares from poorest to richest fifth.
Read the Gini on the 0-to-1 scale and the 0-to-100 index used in international tables.
Compare against the average with our GDP per capita calculator: the pair shows both the size and the split of the pie.
The Gini Formula
Geometrically, the Gini is twice the area between the line of perfect equality and the Lorenz curve, the curve plotting cumulative income against cumulative population. With grouped quintile data, the trapezoid rule approximates that area: each quintile contributes a trapezoid under the curve, and one minus twice the total area is the Gini. Finer groupings give truer numbers; quintiles slightly understate inequality versus microdata because they smooth within-group differences.
Worked Example
Quintile shares of 3, 8, 14, 23, and 52 percent. Cumulative income shares: 3, 11, 25, 48, 100. The trapezoids under the Lorenz curve sum to an area of about 0.29, so Gini = 1 - 2 x 0.29 = 0.452, or 45.2 on the 0-100 scale. For contrast, perfectly equal shares of 20% each give a Gini of exactly 0, and shares of 0, 0, 0, 0, 100 give 0.8 with quintile grouping. Real countries range from about 0.25 in Scandinavia to above 0.6 in the most unequal societies.
What the Gini Misses
Two very different distributions can share one Gini: heavy top-end concentration and a hollowed-out middle can score the same. The index is also blind to absolute levels; a poor equal country and a rich equal country look identical. It says nothing about mobility, whether the poor fifth this year escapes it next year. And it is sensitive to what counts as income: before-tax versus after-tax, with or without transfers, can shift a country's Gini by 0.1 or more, which is why cross-country comparisons need a consistent definition.
My honest read: the Gini is the best one-number inequality summary we have, and one number is never enough. Pair it with the top-1% share and the poverty rate before drawing conclusions. A falling Gini driven by the middle gaining differs completely from one driven by the top losing, and the policy response should differ too.
Estimates for planning only, not financial advice.
Frequently Asked Questions
What is the Gini coefficient?
A 0-to-1 measure of income or wealth inequality. Zero means everyone has the same; one means a single person has everything. Higher values mean more inequality. Most rich countries sit between 0.25 and 0.5.
How is the Gini coefficient calculated?
From the Lorenz curve: it is twice the area between the line of perfect equality and the curve of actual cumulative income. With grouped data like quintiles, the trapezoid rule approximates that area.
What is a good Gini coefficient?
Lower means more equal, but there is no target. Scandinavia sits near 0.25 to 0.30 after taxes and transfers; the US is around 0.41 to 0.48 depending on the income definition. Above 0.5 signals severe inequality.
What is the Gini coefficient of the United States?
Roughly 0.41 on the Census money-income definition and near 0.48 on some broader measures, the highest among major rich economies. After taxes and transfers it falls several points, which shows how much redistribution the US system does.
What is the difference between Gini 0-1 and 0-100?
They are the same number on different scales; multiply by 100. The World Bank and most international tables use 0-100, while academic work usually uses 0-1.
Can two countries have the same Gini but different inequality?
Yes. The Gini summarizes the whole curve in one number, so different shapes, top-heavy versus hollow-middle, can score identically. Supplement it with quintile shares or top-1% data.
Does the Gini measure wealth or income?
Usually income, but wealth Ginis exist and run much higher, often 0.7 to 0.85, because wealth concentrates more than income. Always check which one a cited figure uses.
Why do Gini estimates for one country disagree?
Definitions differ: before or after tax, with or without transfers, households versus tax units, income versus consumption. A US Gini of 0.48 and 0.41 can both be right under different definitions.
Has US inequality risen?
Yes, substantially since about 1980. The top quintile's share rose from the low 40s to over 50 percent while the bottom quintile's share fell. The Gini rose roughly 0.1 over that span.
What lowers the Gini coefficient?
Progressive taxes and transfers mechanically lower after-tax Ginis. Over longer horizons, broader education access, stronger labor bargaining power, and less concentrated capital income compress the distribution.