The world population is expected to grow by one billion over the next dozen years.

According to a new United Nations (U.N.) report, there are currently 7.6 billion people on earth but the count is expected to rise to 8.6 billion by 2030. The world population is expected to reach 9.8 billion in 2050 and 11.2 billion in 2100.

The report estimates about 83 million people are being added to the world each year.

India, with 1.3 billion inhabitants, and China, with 1.4 billion inhabitants, remain the two most populated countries in the earth, making up 18 and 19 percent of the world respectively. However, India is expected to surpass China's population in about seven years, by around 2024.

Nigeria is the fastest growing large country and currently holds the seventh largest population in the world. It's expected to surpass the United States and become the third largest country by 2050, according to the U.N. report.

During the same period, 26 African countries are expected to double in population.

Most of the population growth is expected to be centered in just nine countries: India, Nigeria, the Democratic Republic of the Congo, Pakistan, Ethiopia, the United Republic of Tanzania, the U.S., Uganda and Indonesia.

The U.S. is one of 83 countries making up 46 percent of the population, with lower fertility rates. The U.S. is expected to grow despite lower fertility rates.

The U.N. report also found, lower fertility rates lead to an ageing population. Globally, the number of people aged 80 or over, is projected to triple by 2050, from 137 million in 2017 to 425 million in 2050. By 2100 it is expected to increase to 909 million, nearly seven times what it currently is.

Additionally, there is a higher life expectancy worldwide due to several factors including a lower under-five mortality rate, continuing reductions in fatalities due to HIV/AIDS and progress in combating other infectious as well as non-communicable diseases.