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The Ministry of Health and Family Welfare answered in the upper house to a question that India has a fertility rate of 2.2 (link here). The replacement fertility level is usually given at 2.1 to 2.2.

These sources suggest that India's population is projected to grow at least until 2060 (2050 in some sources): Quartz, The Hindu.

The Quartz article even cits UN population projects and says:

"Even under the instant-replacement fertility variant, with the country’s fertility assumed to fall immediately to 2.1 births per woman, India’s population would reach 1.9 billion by the century’s close."

This source defines the replacement fertility level as:

"Replacement level fertility is the level of fertility at which a population exactly replaces itself from one generation to the next. In developed countries, replacement level fertility can be taken as requiring an average of 2.1 children per woman."

What I don't understand is: how can India's population be projected to grow until 2060 if it has already reached replacement fertility level in 2017? A 'generation' is usually 25 years. Even if we take it as 30 years, India's population should stop growing in a couple of decades. How does the UN project that it'll grow until 2060?

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Population size isn't just about birth rate.

It's also about death rate and net migration.

If the health of India's population continues to improve, then life expectancy will increase, and population size will continue to grow until life expectancy stops increasing, assuming zero net migration.

Net inward migration would also increase the population size.

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  • $\begingroup$ India's net migration is 0. Source. The replacement fertility rate should, by definition, take into consider life expectancy and death rates. The sole reason why developed countries have a lesser replacement fertility rate than developing countries is because of the differences in death rates. $\endgroup$ – WorldGov Mar 4 '18 at 21:16
  • $\begingroup$ You're welcome. Not sure I can explain it any clearer, though. Please do re-read the third paragraph, and let me know why you find it unclear. $\endgroup$ – EnergyNumbers Mar 4 '18 at 21:25
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It's important to consider the age structure of the population, often represented by a population pyramid as shown here. At present, India's population in the main 5-year groups of child-bearing age, from 15 to 39, is much larger than in the 5-year groups from 40 to 64. To a small extent, that reflects deaths below age 64, but the main reason is past population growth.

Even if the birth rate of children of the current 15-39 groups is only at replacement rate, India's total population will continue to grow. What is now the 15-39 group will in 25 years time be the 40-64 group, and (barring a huge increase in deaths below 64) will be considerably larger than the current 40-64 group. So in 25 years time the 40-64 group will be larger than now, but all younger groups will be at least as large as now.

In fact, India's population can be expected to grow for longer than 25 years because the youngest 5 year groups (0-14) are in turn somewhat larger than most of the 15-39 groups.

This phenomenon is known as population momentum.

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