This brief proposes estimates of the loss in on-the-job learning due to the COVID-19 pandemic. Participation in informal learning due to widespread shutdowns of economic activities is estimated to have decreased by 25%. In the case of non-formal learning the estimate corresponds to 18%. This represents a notable amount of lost learning, and one which may not be easily recovered. Estimated learning losses are highly heterogeneous across sectors and individuals, and depend on the pervasiveness of shutdowns of economic activities. Workers employed in administrative and support service activities; in the arts, entertainment and recreation, are expected to lose, on average, nearly three-quarters of informal and non‑formal learning opportunities per week. Results also show that the pandemic likely led to fewer learning opportunities for disadvantaged and low-skilled workers who, in turn, are most likely going to need retraining.