Coastal waters play a unique role in carbon cycling, processing carbon transported from rivers to the open ocean. Biogeochemical models depicting these waters often ignore the impact of macrobiota, such as bivalves, which take in calcium, alkalinity, and dissolved inorganic carbon to synthesize their calcium carbonate (CaCO₃) shells during calcification. The extent to which calcification impacts carbon cycling in the Chesapeake Bay, a large coastal plain estuary, has previously been unexplored. Calcification can be estimated from macrobenthic production (P_org), the synthesis of organic carbon by benthic macrofauna. We examined two models of P_org, one solely as a function of biomass and the other of both biomass and water temperature. An extensive benthic biomass and water temperature history collected by the Chesapeake Bay Benthic Monitoring Program from 1995 to 2022 was used as input to these models. The average bay-wide calcification rate for the biomass-temperature model was 99 g CaCO₃ m^-2 yr^-1; for the biomass-only model, the rate was 162 g CaCO₃ m^-2yr^-1. The temperature-dependent model estimated a nearly twofold increase in calcification from winter to summer. Macrobenthic calcification is roughly 10% of the riverine calcium flux to the Bay, estimated from measurements of riverine calcium concentration and streamflow from the United States Geological Survey. As dissolved inorganic carbon and alkalinity are proportional to riverine calcium, we expect a similar fraction of removal of these constituents by macrobenthic calcification. Our results suggest that benthic macrofauna should be included in estuarine biogeochemical models.