Gini Coefficient

Imagine 10 friends gathered to share 10 whole pizzas. The most equal scenario is when everyone gets exactly one pizza. In this state with zero income inequality, the Gini coefficient is 0. But if one person hoards all 10 pizzas while the remaining 9 get nothing, the score spikes to 0.9. As the population grows larger, this extreme value gets closer to its maximum of 1.

Real societies always fall somewhere between these two extremes. Economists line up citizens from the lowest earners to the highest. Then, they plot this distribution on a graph called the Lorenz curve, comparing the cumulative share of the population against the cumulative share of total income.

The Gini coefficient calculates the area of the gap between the straight line of perfect equality and the curved line of actual income distribution. The wider this gap grows, the deeper the divide between rich and poor. When the curve sags further downward, inequality is worse.

In the end, the Gini coefficient captures a society's distribution in a single number between 0 and 1. Without wading through complicated economic statistics, it lets you compare income inequality across different countries at a glance.

The Gini coefficient is usually recorded to two or three decimal places. Economists use this figure to see whether a society's economic balance is holding steady. International organizations and media outlets often point to 0.4 as an informal warning line for high inequality. Still, this is a rule of thumb rather than a strict law. Its meaning changes depending on whether it measures market wages, net income, or assets.

Countries scoring between 0.2 and 0.3 are generally viewed as having relatively fair income distribution. In contrast, societies with a Gini coefficient above 0.5 are classified internationally as experiencing very high inequality.

The Gini coefficient you usually see in the news is calculated based on annual household income. Governments monitor whether this figure rises or falls each year to design policies that address the wealth gap.

A rising Gini coefficient means income distribution has become more unequal. Many nations use progressive tax brackets and welfare programs to keep inequality under control. However, structural demographic shifts—such as rapid aging or an increase in single-person households—can nudge the number upward on their own, so a rising score does not automatically mean fairness is failing.

Looking more closely, a country's Gini coefficient looks different before and after the government collects taxes and distributes aid. The metric calculated from paychecks, business earnings, interest, and rent earned directly in the market is called the market income Gini. The figure calculated after paying taxes and receiving welfare benefits is called the disposable income Gini.

When governments tax high earners more and support households in need, the disposable income Gini drops lower than the original market income Gini. A larger gap between the two numbers shows that government redistribution policies are effectively narrowing the gap between rich and poor.

However, standard income-based Gini coefficients have clear blind spots. Because they track the money a household takes in over a single year, they overlook wealth accumulated over decades, such as real estate, stocks, and family savings.

Two households may earn similar annual salaries, but their living standards diverge if one owns prime real estate and the other rents. That is why economists calculate wealth Gini coefficients and compare income quintile ratios alongside the standard Gini coefficient.