<p>Population size isn't just about birth rate.</p>

<p>It's also about death rate and net migration.</p>

<p>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.</p>

<p>Net inward migration would also increase the population size.</p>

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2018-03-04T21:16:05.910Z
India's net migration is 0. [Source](https://www.cia.gov/library/publications/the-world-factbook/fields/2112.html). 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.
WorldGov
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2018-03-04T21:25:25.800Z
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.
410 gone
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2018-03-04T20:51:54.673Z
2018-03-04T20:51:54.673Z
410 gone
<p>The UN Population Division's <a href="https://population.un.org/wpp/Graphs/Probabilistic/POP/TOT/356" rel="nofollow noreferrer"><em>median</em> projection for India</a> shows population growing until around 2060.  Continuing growth despite replacement level fertility is a consequence of the  age structure of the population which, following common practice, the UN represents by a <a href="https://population.un.org/wpp/Graphs/DemographicProfiles/Pyramid/356" rel="nofollow noreferrer">population pyramid</a>. At present, India's population in groups up to age 40 is larger than in the 40-50 groups and much larger than in groups over 50.  That is partly due to deaths among older groups but to a considerable extent it reflects past population growth, with each 5 year age group (until the under 10 groups) being larger than the one before.</p>
<p>With replacement level fertility, future births will result in 5 year groups of about the same size as those in the current 0 to 40 range.  But population growth can still occur as the current 0 to 40 groups become older.  In 40 years time the 0 to 40 groups will have become the 40-80 groups, and barring a huge increase in death rates will be much larger than the current 40-80 groups.</p>
<p>This phenomenon is known as population momentum (for further explanation see <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3987379/pdf/FVVinObGyn-5-281-291.pdf" rel="nofollow noreferrer">Bavel 2013</a> pp 288-9).</p>

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2018-03-04T23:07:55.910Z
2021-04-04T11:31:25.940Z
2021-04-04T11:31:25.940Z
Adam Bailey
<p>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 <a href="http://164.100.47.234/question/annex/242/Au2958.pdf" rel="nofollow noreferrer">here</a>). The replacement fertility level is usually given at 2.1 to 2.2. </p>

<p>These sources suggest that India's population is projected to grow at least until 2060 (2050 in some sources): <a href="https://qz.com/1051533/india-is-unprepared-for-a-near-future-when-it-will-be-the-worlds-most-populous-country/" rel="nofollow noreferrer">Quartz</a>, <a href="http://www.thehindu.com/news/national/indias-fertility-rate-more-than-halves-over-40-years/article19124554.ece." rel="nofollow noreferrer">The Hindu</a>. </p>

<p>The Quartz article even cits UN population projects and says: </p>

<blockquote>
  <p>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.</p>
</blockquote>

<p><a href="https://www.ncbi.nlm.nih.gov/pubmed/7834459" rel="nofollow noreferrer">This source</a> defines the replacement fertility level as: </p>

<blockquote>
  <p>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.</p>
</blockquote>

<p>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?</p>

<population-economics><demographics>
How long can a population grow once it has reached the replacement fertility rate?
WorldGov
# How long can a population grow once it has reached the replacement fertility rate?

(Asked by: username_0 on 2018-03-04)

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](http://164.100.47.234/question/annex/242/Au2958.pdf)). 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](https://qz.com/1051533/india-is-unprepared-for-a-near-future-when-it-will-be-the-worlds-most-populous-country/), [The Hindu](http://www.thehindu.com/news/national/indias-fertility-rate-more-than-halves-over-40-years/article19124554.ece.).

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](https://www.ncbi.nlm.nih.gov/pubmed/7834459) 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?

**Tags:** population-economics, demographics

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## 2 answers

### Answer by username_1 on 2018-03-04. Score: 2 | Accepted answer

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.

> **Comments:**
> **username_0**: India's net migration is 0. [Source](https://www.cia.gov/library/publications/the-world-factbook/fields/2112.html). 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.  
> **username_1**: 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.  

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### Answer by username_2 on 2018-03-04. Score: 2

The UN Population Division's [*median* projection for India](https://population.un.org/wpp/Graphs/Probabilistic/POP/TOT/356) shows population growing until around 2060. Continuing growth despite replacement level fertility is a consequence of the age structure of the population which, following common practice, the UN represents by a [population pyramid](https://population.un.org/wpp/Graphs/DemographicProfiles/Pyramid/356). At present, India's population in groups up to age 40 is larger than in the 40-50 groups and much larger than in groups over 50. That is partly due to deaths among older groups but to a considerable extent it reflects past population growth, with each 5 year age group (until the under 10 groups) being larger than the one before.

With replacement level fertility, future births will result in 5 year groups of about the same size as those in the current 0 to 40 range. But population growth can still occur as the current 0 to 40 groups become older. In 40 years time the 0 to 40 groups will have become the 40-80 groups, and barring a huge increase in death rates will be much larger than the current 40-80 groups.

This phenomenon is known as population momentum (for further explanation see [Bavel 2013](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3987379/pdf/FVVinObGyn-5-281-291.pdf) pp 288-9).


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