IT IS well known that parenthood tends to hurts women’s careers but not men’s. Numerous studies have shown that as a group, having children lowers women’s lifetime earnings, an outcome known as the “child penalty”. A wide range of individual decisions account for this effect. Some women work fewer hours, or not at all, when their children are young. Others switch to jobs that are more family-friendly but lower-paid. There is also substantial variation in the size of the earnings decline, ranging from zero all the way up to 100% (in the case of women who stop working altogether).

One new academic paper uncovers an intriguing factor that helps to predict whether the reduction in a woman’s income due to having children is likely to be large or small: the choices made during her childhood by her own mother. The study’s authors, Henrik Kleven from Princeton University, Camille Landais from the London School of Economics and Jakob Sogaard from the Danish Ministry of Taxation, used administrative data from Denmark, which covers the country’s entire population for generations. They defined the child penalty as the amount by which women’s earnings fell behind those of men after having children.

From 1980 to 2013, the long-run child penalty was about 20%. Because the overall pay gap between men and women shrank during that period, by 2013 the child penalty accounted for almost the entire remaining difference in the sexes’ incomes. Before becoming mothers, women’s compensation more or less keeps pace with men’s. Only once they have children do their economic trajectories begin to lag.

As the researchers explored potential causes for this phenomenon, they noticed that women who grew up in families in which the mother worked a lot relative to the father tended to suffer relatively small child penalties. Conversely, those who grew up with stay-at-home mothers were more likely to scale back their careers. This suggests that women are heavily influenced by the examples set by their own mothers when deciding how to balance work and family. Tellingly, the working patterns of a woman’s parents-in-law made no difference to her child penalty, suggesting that women’s decisions are not influenced by preferences that their partners may have formed during childhood.

All of which is a lesson to those mothers who want their daughters to bridge the gender pay gap. Their wishes are more likely to come true if they lead by example when their girls are young.