Threatening situations have been shown to influence prosocial and altruistic behaviour in laboratory studies. However, it is unknown whether those effects would transfer to a real-life crisis like the COVID-19 pandemic. In this study, we examined the impact of changing COVID-19 threat on everyday altruism. Specifically, we investigated the association between defensive emotions associated with varying levels of perceived threat imminence, and reported frequency of altruistic behaviours. A sample of 600 United States residents was recruited online via Prolific at 4 different timepoints in March and April (n=150 each week). We collected self-report measures of everyday altruism, Perceived COVID-19 threat, and defensive emotions associated with varying threat imminence (anticipatory versus acute anxiety). Linear mixed effects models were used to predict variation in everyday altruism as a function of perceived COVID-19 threat and defensive emotions. Our results revealed a clear and consistent association between acute anxiety in response to the pandemic, and frequency of altruistic behaviours. No significant association was found between altruism and less acute defensive responses. These results suggest acute defensive emotions associated with higher threat imminence may promote altruistic action during a real-life crisis.