Background: While fertility rates have decreased during the second half of the 20th century in Japan, little is known regarding trends in the number of children that men and women have across birth cohorts and whether these differ by education and income.
Methods: We used data from four rounds of the National Fertility Survey (1992, 2005, 2010 and 2015) and included men and women aged 40-49 years (16728 men and 17628 women). By 5-year birth cohorts, we assessed the distribution of number of children (0, 1, 2 and 3 or more) and total fertility (the mean number of children) at completed fertility (age 45-49 or 40-44 years depending on birth cohort). We assessed trends in these fertility outcomes in men and women separately, and by education (no university education; university education) for men and women and by reported annual income (0 to <3 000 000 JPY; 3 000 000 to <6 000 000 JPY; ≥6 000 000 JPY) for men.
Results: When comparing those born in 1943-1948 with those born in 1971-1975, the proportion with no children had increased from 14.3 to 39.9% for men and from 11.6 to 27.6% for women. This increase coincided with a decrease in the proportions of individuals with 2 or more children. Total fertility had decreased from 1.92 to 1.17 among men and from 1.96 to 1.42 among women. For men, those with a university degree were more likely to have children than those without a university degree in all birth cohorts except 1943-1947. Men with higher income were more likely to have children across birth cohorts. While the proportion who had children had decreased in all income groups, the decrease was steeper among those in the lowest income group. Among women born 1956-1970, those with a university degree were less likely to have children than those without a university degree; this difference was no longer seen among those born 1971-1975. For both men and women, trends in having children and total fertility across birth cohorts did not differ by educational status.
Conclusions: The decline in the total fertility rate in Japan can be attributed to both an increasing proportion of the population who have no children and a lower number of children among those who have children. Men with lower education and income were less likely to have children and the disparity in the number of children that men have by income had increased in more recent birth cohorts. Among women, higher education was associated with lower fertility, although this pattern was no longer observed among those born in 1971-1975.