India's population is expected to reach 1,425,775,850 people by the end of April, the new data shows.
A different UN body last week predicted that India would overtake China by the middle of this year.
The Asian nations have accounted for more than a third of the global population for over 70 years.
"China will soon cede its long-held status as the world's most populous country," the UN's Department of Economic and Social Affairs (DESA) said in a statement.
It added that "due to the uncertainty associated with estimating and projecting populations, the specific date on which India is expected to surpass China in population size is approximate and subject to revision".
The UN Population Fund said last week India would have 2.9 million more people than China by the middle of 2023.
China's birth rate has plunged recently, with its population shrinking last year for the first time since 1961.
China's population could drop below 1 billion before the end of the century, DESA said.
"By contrast, India's population is expected to continue growing for several decades," it added.
However, fertility rates are dropping in India, too - from 5.7 births per woman in 1950 to 2.2 births per woman today.
In November, the global population crossed 8 billion. But experts the growth is not as rapid as it was - and is now at its slowest rate since 1950.