When does fertility in a country become so low or so high that a government needs to intervene? This paper sheds light on this population policy question, based on a worldwide survey among demographers. We examine how professionals’ policy preferences regarding fertility levels are affected by their views on the impacts of population growth/decline and by fertility in their country of residence. The median respondent suggests intervention once fertility goes below 1.4 children or above 3.0. Three results stand out: first, demographers who are concerned about the carrying capacity of the earth are more willing to intervene than those who are less concerned. Second, the context of decision-making matters: experts living in high-fertility countries are more set on intervention than those living in low-fertility countries, but their threshold fertility level is also higher. Third, political orientation matters: right-leaning demographers are more set on government intervention than left-leaning demographers.