Fall freeze-up and spring break-up are defining dates in the sea-ice seasonal cycle for coastal processes, biological habitat, subsistence harvests & maritime access throughout the Arctic. We developed an algorithm to extract key sea-ice seasonality indicators from passive microwave remote sensing data at the pan-Arctic scale, building on coastal observations and past work in the Alaska Arctic. Key findings include: (i) trends towards later freeze-up and earlier break-up observed throughout most of the Arctic, with contrasts between coastal and offshore regions;(ii) freeze-up and break-up can serve as key indicators for coastal users, incl. communities, maritime transport, and other activities, with gridded indicator data serving as a link to earth-system model output, (iii) linkages between sea ice seasonality and terrestrial summer warmth and vegetation indices detected in Alaska require further attention, including model-based process studies and pan-Arctic projections.