With 1.37 billion people, China currently has the world's largest population. It will peak at 1.45 billion in 2029, compared with a peak of 1.4 billion in 2023 if the "one-child" policy that restricted most urban couples to one child and rural couples to two if their first was a girl had continued, according to the study, published in the medical journal Lancet.
It was revised over the years to allow more couples to have an additional child, until the government allowed all married couples to have two children beginning this year, mainly to combat an aging population.
One of the study's authors, Zeng Yi of Peking University, said that it was the first such analysis to fully consider rural-urban differences and the effects of migration when quantifying the impact on population growth.
The study says it assumes that the total fertility rate, or births per woman, will rise from the current 2.01 in rural areas and 1.24 in urban areas to 2.15 and 1.67, respectively, in the next decade.
More From This Section
Cai Yong, a demographer at the University of North Carolina at Chapel Hill who wasn't involved in the study, said he thought its total fertility rate projection of 1.81 in 2030 was "overly optimistic."
Lower fertility in China "is no longer a depressed result of restrictive policy," Cai said, adding that Chinese are likely to opt to pour their resources into just one "high quality" child instead of multiple children. They are also increasingly postponing or forgoing marriage and childbearing, he said.
The Lancet paper's researchers in Britain and China say the effects of the new policy on China's shrinking work force and aging population won't be seen for two decades.