Abstract The spotted lanternfly, Lycorma delicatula (White, 1845), is an invasive species in the United States. This pest causes damage to vineyards and has the potential to negatively affect other crops and industries. Information describing the seasonal timing of life stages can improve its management. In 2019 and 2020, spotted lanternfly seasonal activity was followed weekly from spring egg hatch to the first hard freeze. Weighted mean timing of activity for each nymphal instar, early adults, late adults, total adults, and egg mass deposition are presented for 2019 and 2020 on Acer rubrum and 2020 on Ailanthus altissima. Logistic equations describing the percentage completion of each activity period on these hosts were fitted using a start date of 1 January to calculate accumulated degree days (ADD). For the adult and egg mass deposition periods, we additionally used a biofix of the date adults were first observed to calculate ADD. ADD from 1 January adequately estimated the timing of nymphal instars but ADD from observation of the first adult better estimated the timing of adult activity and egg mass deposition. Late adult activity and egg mass deposition periods appeared to be influenced by another environmental cue, such as day length. Maps of season-long ADD show that spotted lanternflies are unlikely to reach adulthood in colder regions of the northeast United States, and therefore may not establish there. We also report a strong seasonal trend in sex ratio on A. rubrum, where the population shifted from over 80% male to over 80% female in October.