The COVID-19 pandemic presents challenges to psychological well-being, but how can we predict when people suffer or cope during sustained stress? Here we examine the role of emotional experiences for well-being during the prolonged stress of the COVID-19 pandemic. - Study 1 compared the relative importance of emotional experiences for well-being before versus during the pandemic using pre-registered analyses with national representative samples. Negative emotional experiences were more detrimental and positive emotional experiences less protective for well-being during the pandemic. Study 2 used survey data collected from 26,684 participants in 51 countries during the COVID-19 outbreak. We show that, across countries, well-being is linked to individuals’ recent emotional experiences, including calm, hope, anxiety, loneliness, and sadness. Consistent results are found in two representative samples with pre-registered analyses (Study 3). A prospective 30-day daily diary study confirms the key role of these five emotions, and demonstrates that emotional experiences precede changes in well-being (Study 4). Our findings highlight differential relationships between specific types of momentary emotional experiences and well-being, and point to the cultivation of calm and hope as candidate routes for well-being interventions during periods of sustained stress.