Using the Kenya Demographic Health Survey 2014, this article estimates the motherhood penalty in Kenya’s labour market. To control for endogeneity, the study used mixed-sibling sex preference to explain the exogenous variation in fertility. The results from the auxiliary regression show the existence of ‘mixedsibling’ sex preference in Kenya. The probability of having an additional child increases by 24.77 per cent for women whose first two children are the same sex. The instrumental variable model shows that the exogenous variation in fertility afforded by mixed-sibling sex preference significantly reduces the probability of women’s labour supply for decent work by 4.29 per cent. The effect of fertility is heterogeneous across age groups. The article finds that labour supply for decent work reduces by 6.08 per cent and 8.29 per cent for women in the age groups 15–24 and 24–34, respectively. Policy incentives such as providing access to affordable childcare services are critical in reducing the motherhood penalty.
