We have seen before how fertility rates have come down, some faster than others, but all of them nonetheless. I had promised you to do the math to show that the overall population would grow for some more time before plateauing. Today, we will do that. So, we join the celebrations of Indians who just made it to 2.0 last year.
The calculations are fairly basic, as the objective is to prove the point, not accuracy. We’ll start with the last census, the 2011 census. The following two graphs summarise the data.
The ages are grouped in blocks of 5 years; therefore, we take 5-year steps in our calculations. In each step, we jump once to the next bucket. So people in 0-4 become part of 5-9, and so on. In the process, we multiply the survival chance of each age group using life tables presented in the census portal. That leaves the newborn group – 0-4 – to be filled up. We add up four groups that cover women from age 20 to 40 and divide by 4 to standardise and multiply with the average fertility rate, starting with 2.1 in 2011 and reducing by 0.01 per year until it reaches a steady rate of 1.85 (remember, in 2020 it became 2.0).
The results after a few years are in the following plot.
Now, we will plot the total population for all these years until 2061.
It is quite reassuring that this simple treatment was not far from the more advanced forecasting done by The Lancet in 2020, which forecasted a peak population of 1.6 B in 2048.
In Summary
The flurry of incoming guests has certainly come down. But the population hotel has many vacant rooms to occupy, thanks to the extraordinary decades of prosperity and good public health. They have to be filled up first before the number of people checking out can match the fresh inmates!
Fertility, Mortality, and Population Scenarios for 195 Countries: The Lancet
Life Table: Census India
Life Table: Wiki Page
