UK aid saves millions of lives each year, making the world healthier, more peaceful and prosperous. As a result, more countries are moving from low- to middle-income status. Transition is the process whereby donors reduce or change the type of support they provide to a country, often based on economic indicators. But these indicators don’t take health standards, inequality or a government’s budgetary and technical capacity into account. With multiple donors withdrawing funding simultaneously, many countries are facing sudden and enormous funding shortfalls that they are realistically unable to meet. The implications for access to healthcare, particularly for the most vulnerable communities, are enormous and risk decades of hard-won progress. To prevent unnecessary deaths and deliver the promise of the Sustainable Development Goals (SDGs), we need to significantly improve how we manage these transition processes.