# How are the HDI aggregates obtained for country groups?

The aggregation of the HDI across countries in a group (HD category, developing region, etc.) is done by applying the HDI formula to the weighted group-averages of component indicators. The weights used to obtain such averages of component indicators are – total population for life expectancy and gross national income per capita, population (ages 5 to 24) for expected years of schooling and population (ages 25 and above) for mean years of schooling.