The aim of this study was to examine the positive relationship between religiosity and fertility from the perspective of perceived consequences of parenthood. Previous studies in Germany have found that highly religious people ascribe higher benefits and lower costs to having children. Furthermore, the impact of costs and benefits on fertility is less pronounced among the highly religious. This study tested these mechanisms for fertility intentions and in the context of Poland – a country with a low fertility rate and high religiosity in comparison to other European countries. A sample of 4892 men and women of childbearing age from the second wave of the Polish version of the Generations and Gender Survey conducted in 2014/2015 was used. First, the extent to which perceived costs and benefits mediate the impact of religiosity on fertility intentions was analysed. Second, whether religiosity moderates the impact of perceived costs and benefits on fertility intentions was investigated. The results show that part of the positive effect of religiosity on fertility intentions can be explained by more-religious people seeing higher benefits of having children. Furthermore, but only in the case of women, religiosity moderates the impact of perceived costs on fertility intentions, suggesting that the effect of perceived costs decreases with increasing religiosity.