India is poised to overtake China as the most populous country by 2050, according to recent findings from the Population Reference Bureau.

India’s population is expected to swell to 1.62 billion, from just over a billion at present, while China will inch up to 1.43 billion, at a slower pace from 1.3 billion, the Washington-based nonprofit found.

While the world’s population is expected to grow overall by 45% to 9.3 billion by 2050, America is the only developed country that will experience significant population growth, which will primarily be due to immigration, rather than increased birth rates. America is expected to grow by 50% to 420 million by 2050. America, Russia, and Japan are all on the World’s Largest Countries in 2004 list, but only America is expected to remain on the list for 2050.

A population’s current age demographic plays a large part in the bureau’s estimates. In Japan, only 14% of the population is below age 15, and 19% is above age 65.

By contrast, in Nigeria, half of the population is below age 15, and only 3% is above 65. Japan’s population is expected to shrink to 100.6 million in 2050 from 127.6 million now, while Nigeria’s population is anticipated to mushroom to 307.4 million from 137.3 million today.

Niger is expected to have the fastest growth; by 2050 its population will quadruple to 53 million from 12 million, according to the study.

Europe is the only stagnant region according to the bureau, and in some cases, instead of merely tapering growth, populations will actually deteriorate. Bulgaria’s population is expected to decline to 4.8 million from 7.8 million. Overall, 28 countries in Europe will experience population declines by 2050.

The study’s findings are based on assumptions on the future course of fertility, mortality, and migration, official country projections, and series issued by the U.N. and the U.S. Census Bureau. Changes in migration and birth rates can affect the findings, according to the bureau.