Objective: To examine the effect of the timing of a woman's first birth on her midlife earnings, and the potential mediators of this effect.

Background: While many studies demonstrate that motherhood substantially affects women’s wages and earnings, there is less research on the impact of the timing of entry into motherhood, particularly in the long term and in contexts outside the US.

Method: We analysed data on women who gave birth for the first time between the ages of 15 and 30, taken from the 1970 British Cohort Study. Within the framework of instrumental variable regression, our preferred specification utilised the occurrence of contraceptive failure as a source of exogenous variation in the age at first birth.

Results: We found tentative evidence that a higher age at first birth led to a higher probability of being employed in midlife. At the same time, a higher age at first birth reduced the earnings level of employed mothers in midlife. This was because a later first birth often resulted in mothers working part time rather than full time. Furthermore, a higher age at first birth decreased the time until the second birth, while increasing the probability of having a co-resident partner who could contribute to the household income.

Conclusion: These findings suggest that the impact of having an early first birth on earnings in midlife is not uniformly negative.