How did human capital develop in the Polish-Lithuanian Commonwealth and other east-central and eastern European countries? We trace the development of a specific human capital indicator during this period: numeracy. We draw upon new evidence for Poland, Belarus, Ukraine, Lithuania, and Russia, controlling for potential selectivity issues. Numeracy started at low levels, especially in Russia and, later, in Lithuania. In the mid-18 th century, levels in Russia began to converge to Polish levels; later, the other regions followed. We test potential determinants such as serfdom, female autonomy, nutrition and geography. We find that female autonomy proxied by the share of young female singles had a particularly consistent positive effect. An instrumental variable regression suggests that the relationship could be causal.