As significant as the shift from quantity to quality in fertility decisions, a rise in the median age at first birth has been commonly observed in the more developed world. This paper attempts to understand the latter demographic trend from the empirical perspective. We first construct a conditional hazard model that incorporates determinants of birth spacing, with a primary emphasis on human capital and personal preference factors. We then examine the importance of these factors, using a rich data set comprised of a selected sample of women from various cohorts reported in the 1980 Taiwan Census. Our results show that, in addition to the age at marriage, human capital factors such as the woman’s education, job security and occupation are all significant in influencing the first spacing. The roles played by these human capital factors become even more important for the second spacing. In the third spacing, the relative importance of education and occupation still persists, while gender preferences become much stronger. Overall, while job security shortens the timing of childbearing, better education and occupation as well as more girls from previous births all lead to delays in births. As for preference factors, we find that elementary school teachers have a shorter birth-spacing compared to junior high school teachers, indicating possible personal preferences for children that are consistent with women’s job selection.