This article is motivated by potential changes to fertility and migration patterns that may result from major global economic and/or health crises such as the COVID-19 global pandemic. The focus is on the long-term effects of changes to fertility and migration on both discounted national output per capita and intergenerational income distribution. Simulations are based on United Nations population projections, applied to 15 countries. Lower fertility and lower immigration are generally positive for discounted output per capita and raise the lifetime incomes of smaller cohorts. While lower immigration also raises the lifetime incomes of smaller cohorts, it has a lower impact on discounted output per capita.