Several decades of internal migration have brought half a billion people into the cities. Six out of 10 Chinese now live in urban areas, compared with two in 10 four decades ago. In 1990, only 3 percent of college-age Chinese attended college; in 2015, the number was more than 40 percent for men and 45 percent for women. Today, Chinese women — armed with new knowledge, living independently in vibrant cities and determined to pursue their own goals — are less likely than previous generations to let their personal and reproductive decisions be influenced by pressure from the state or their families. In 1990, virtually every woman in China was married by the age of 30, according to official census data. In 2015, one in 10 women had not married by 30; in Shanghai, it was one in five.

Low fertility has its benefits. Fewer children probably means that more attention is paid to them, including in the form of more investment in education. China’s population may be older overall, but it also is wealthier, a fact that has brought new economic opportunities, such as more health care related products and services, and greater spending on leisure. The declining size of the work force and rising labor costs together drive up demand for labor-saving technologies, from automation to artificial intelligence.

But fertility in China has dropped even as life expectancy has increased, and that combination has translated into the population’s aging overall — which, in turn, has meant an increasing economic burden on working-age people. Since 2010, the number of Chinese people between the ages of 20 and 24, for example, dropped by about 30 percent (from more than 127 million to about 90 million), even as the number of people ages 60 and above increased by almost 39 percent (from 180 million to nearly 250 million). Based on our analysis of official statistics and other population data, we estimate that by 2030 the 20-to-24 age group will shrink by another 20 percent (to around 73 million), while the 60-plus category will grow by 56 percent (and reach 390 million). By then, Chinese people 60 and older will account for more than one-quarter of the total population.

These changing demographics create major political tests for China’s leaders, present and future. One is how to maintain growth as the population keeps aging and the work force’s relative size keeps shrinking. Another is how to deliver the economic and social benefits that Chinese people now expect from the state.