What will the human population be in the year 2100?

Japan has a fertility rate of 1.4 children per woman and to sustain the population it needs to be 2.1 perwoman

• The current Japanese population is 127.5 million with using those statistics that the current fertility rate is 1.4 and the sustained population level is 2.1 with using those statistics how do I calculate the estimated Japanese population in the year 2100?

• Answer:

  Lets assume 80 years lifespan? If cpw is 2.1 then in 2080 there should be 127.5 mil ppl. If cpw is 1.4 then there will be a deficit of .7 ppl in 80 years That is 127.5 * 0.7 = 89.25mil ppl (2080) Now, lets work out 100 years: The decline will be 127.5 -89.25 = 38.5 (80 years) Work out the decline for 100 years: (38.5 / 80) *100 = 47.81 mil Thus the population in Japan in 2100 if lifespan is 80 years will be: 127.5 - 47.81 = 79.69 mil people