Fertility rate is calculated by dividing every age group in the country into groups and multiplying them by how many children that age group are currently having to estimate how many children a woman is going to have during their lifetime. So if today’s women have on average 1 kid in their 20s and 1 kid in their 30s, and none after, that will give a fertility rate of 2.0, no matter how many women are actually in their 20s or 30s. So there being a lot of old people does not change the results. Fertility rate is dependent on how many children women have during their reproductive years. Birth rate however is affected by their being a lot of old people because birth rate numbers are just the number of children born per year per a 1000 people. So the birth rate of Japan would look comparably much worse than the fertility rate. Fertility rate is therefore considered to be a fairer metric.
Not sure how exactly fertility rates are calculated but with countries like Japan the age of the population might play a role too.
Fertility rate is calculated by dividing every age group in the country into groups and multiplying them by how many children that age group are currently having to estimate how many children a woman is going to have during their lifetime. So if today’s women have on average 1 kid in their 20s and 1 kid in their 30s, and none after, that will give a fertility rate of 2.0, no matter how many women are actually in their 20s or 30s. So there being a lot of old people does not change the results. Fertility rate is dependent on how many children women have during their reproductive years. Birth rate however is affected by their being a lot of old people because birth rate numbers are just the number of children born per year per a 1000 people. So the birth rate of Japan would look comparably much worse than the fertility rate. Fertility rate is therefore considered to be a fairer metric.
Sure but economically states are worried about births— they need population replacement to persist